Commit Graph

168 Commits

Author SHA1 Message Date
Linus Torvalds
14d4cc0883 This adds a memzero_explicit() call which is guaranteed not to be
optimized away by GCC.  This is important when we are wiping
 cryptographically sensitive material.
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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull /dev/random updates from Ted Ts'o:
 "This adds a memzero_explicit() call which is guaranteed not to be
  optimized away by GCC.  This is important when we are wiping
  cryptographically sensitive material"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  crypto: memzero_explicit - make sure to clear out sensitive data
  random: add and use memzero_explicit() for clearing data
2014-10-24 12:33:32 -07:00
Daniel Borkmann
d4c5efdb97 random: add and use memzero_explicit() for clearing data
zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
memset() calls which clear out sensitive data in extract_{buf,entropy,
entropy_user}() in random driver are being optimized away by gcc.

Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
that can be used in such cases where a variable with sensitive data is
being cleared out in the end. Other use cases might also be in crypto
code. [ I have put this into lib/string.c though, as it's always built-in
and doesn't need any dependencies then. ]

Fixes kernel bugzilla: 82041

Reported-by: zatimend@hotmail.co.uk
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
2014-10-17 11:37:29 -04:00
Christoph Lameter
1b2a1a7e8a drivers/char/random: Replace __get_cpu_var uses
A single case of using __get_cpu_var for address calculation.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2014-08-26 13:45:45 -04:00
Linus Torvalds
f4f142ed4e Cleanups and bug fixes to /dev/random, add a new getrandom(2) system
call, which is a superset of OpenBSD's getentropy(2) call, for use
 with userspace crypto libraries such as LibreSSL.  Also add the
 ability to have a kernel thread to pull entropy from hardware rng
 devices into /dev/random.
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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness updates from Ted Ts'o:
 "Cleanups and bug fixes to /dev/random, add a new getrandom(2) system
  call, which is a superset of OpenBSD's getentropy(2) call, for use
  with userspace crypto libraries such as LibreSSL.

  Also add the ability to have a kernel thread to pull entropy from
  hardware rng devices into /dev/random"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  hwrng: Pass entropy to add_hwgenerator_randomness() in bits, not bytes
  random: limit the contribution of the hw rng to at most half
  random: introduce getrandom(2) system call
  hw_random: fix sparse warning (NULL vs 0 for pointer)
  random: use registers from interrupted code for CPU's w/o a cycle counter
  hwrng: add per-device entropy derating
  hwrng: create filler thread
  random: add_hwgenerator_randomness() for feeding entropy from devices
  random: use an improved fast_mix() function
  random: clean up interrupt entropy accounting for archs w/o cycle counters
  random: only update the last_pulled time if we actually transferred entropy
  random: remove unneeded hash of a portion of the entropy pool
  random: always update the entropy pool under the spinlock
2014-08-06 08:16:24 -07:00
Theodore Ts'o
48d6be955a random: limit the contribution of the hw rng to at most half
For people who don't trust a hardware RNG which can not be audited,
the changes to add support for RDSEED can be troubling since 97% or
more of the entropy will be contributed from the in-CPU hardware RNG.

We now have a in-kernel khwrngd, so for those people who do want to
implicitly trust the CPU-based system, we could create an arch-rng
hw_random driver, and allow khwrng refill the entropy pool.  This
allows system administrator whether or not they trust the CPU (I
assume the NSA will trust RDRAND/RDSEED implicitly :-), and if so,
what level of entropy derating they want to use.

The reason why this is a really good idea is that if different people
use different levels of entropy derating, it will make it much more
difficult to design a backdoor'ed hwrng that can be generally
exploited in terms of the output of /dev/random when different attack
targets are using differing levels of entropy derating.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2014-08-05 16:41:50 -04:00
Theodore Ts'o
c6e9d6f388 random: introduce getrandom(2) system call
The getrandom(2) system call was requested by the LibreSSL Portable
developers.  It is analoguous to the getentropy(2) system call in
OpenBSD.

The rationale of this system call is to provide resiliance against
file descriptor exhaustion attacks, where the attacker consumes all
available file descriptors, forcing the use of the fallback code where
/dev/[u]random is not available.  Since the fallback code is often not
well-tested, it is better to eliminate this potential failure mode
entirely.

The other feature provided by this new system call is the ability to
request randomness from the /dev/urandom entropy pool, but to block
until at least 128 bits of entropy has been accumulated in the
/dev/urandom entropy pool.  Historically, the emphasis in the
/dev/urandom development has been to ensure that urandom pool is
initialized as quickly as possible after system boot, and preferably
before the init scripts start execution.

This is because changing /dev/urandom reads to block represents an
interface change that could potentially break userspace which is not
acceptable.  In practice, on most x86 desktop and server systems, in
general the entropy pool can be initialized before it is needed (and
in modern kernels, we will printk a warning message if not).  However,
on an embedded system, this may not be the case.  And so with this new
interface, we can provide the functionality of blocking until the
urandom pool has been initialized.  Any userspace program which uses
this new functionality must take care to assure that if it is used
during the boot process, that it will not cause the init scripts or
other portions of the system startup to hang indefinitely.

SYNOPSIS
	#include <linux/random.h>

	int getrandom(void *buf, size_t buflen, unsigned int flags);

DESCRIPTION
	The system call getrandom() fills the buffer pointed to by buf
	with up to buflen random bytes which can be used to seed user
	space random number generators (i.e., DRBG's) or for other
	cryptographic uses.  It should not be used for Monte Carlo
	simulations or other programs/algorithms which are doing
	probabilistic sampling.

	If the GRND_RANDOM flags bit is set, then draw from the
	/dev/random pool instead of the /dev/urandom pool.  The
	/dev/random pool is limited based on the entropy that can be
	obtained from environmental noise, so if there is insufficient
	entropy, the requested number of bytes may not be returned.
	If there is no entropy available at all, getrandom(2) will
	either block, or return an error with errno set to EAGAIN if
	the GRND_NONBLOCK bit is set in flags.

	If the GRND_RANDOM bit is not set, then the /dev/urandom pool
	will be used.  Unlike using read(2) to fetch data from
	/dev/urandom, if the urandom pool has not been sufficiently
	initialized, getrandom(2) will block (or return -1 with the
	errno set to EAGAIN if the GRND_NONBLOCK bit is set in flags).

	The getentropy(2) system call in OpenBSD can be emulated using
	the following function:

            int getentropy(void *buf, size_t buflen)
            {
                    int     ret;

                    if (buflen > 256)
                            goto failure;
                    ret = getrandom(buf, buflen, 0);
                    if (ret < 0)
                            return ret;
                    if (ret == buflen)
                            return 0;
            failure:
                    errno = EIO;
                    return -1;
            }

RETURN VALUE
       On success, the number of bytes that was filled in the buf is
       returned.  This may not be all the bytes requested by the
       caller via buflen if insufficient entropy was present in the
       /dev/random pool, or if the system call was interrupted by a
       signal.

       On error, -1 is returned, and errno is set appropriately.

ERRORS
	EINVAL		An invalid flag was passed to getrandom(2)

	EFAULT		buf is outside the accessible address space.

	EAGAIN		The requested entropy was not available, and
			getentropy(2) would have blocked if the
			GRND_NONBLOCK flag was not set.

	EINTR		While blocked waiting for entropy, the call was
			interrupted by a signal handler; see the description
			of how interrupted read(2) calls on "slow" devices
			are handled with and without the SA_RESTART flag
			in the signal(7) man page.

NOTES
	For small requests (buflen <= 256) getrandom(2) will not
	return EINTR when reading from the urandom pool once the
	entropy pool has been initialized, and it will return all of
	the bytes that have been requested.  This is the recommended
	way to use getrandom(2), and is designed for compatibility
	with OpenBSD's getentropy() system call.

	However, if you are using GRND_RANDOM, then getrandom(2) may
	block until the entropy accounting determines that sufficient
	environmental noise has been gathered such that getrandom(2)
	will be operating as a NRBG instead of a DRBG for those people
	who are working in the NIST SP 800-90 regime.  Since it may
	block for a long time, these guarantees do *not* apply.  The
	user may want to interrupt a hanging process using a signal,
	so blocking until all of the requested bytes are returned
	would be unfriendly.

	For this reason, the user of getrandom(2) MUST always check
	the return value, in case it returns some error, or if fewer
	bytes than requested was returned.  In the case of
	!GRND_RANDOM and small request, the latter should never
	happen, but the careful userspace code (and all crypto code
	should be careful) should check for this anyway!

	Finally, unless you are doing long-term key generation (and
	perhaps not even then), you probably shouldn't be using
	GRND_RANDOM.  The cryptographic algorithms used for
	/dev/urandom are quite conservative, and so should be
	sufficient for all purposes.  The disadvantage of GRND_RANDOM
	is that it can block, and the increased complexity required to
	deal with partially fulfilled getrandom(2) requests.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Zach Brown <zab@zabbo.net>
2014-08-05 16:41:22 -04:00
Hannes Frederic Sowa
79a8468747 random: check for increase of entropy_count because of signed conversion
The expression entropy_count -= ibytes << (ENTROPY_SHIFT + 3) could
actually increase entropy_count if during assignment of the unsigned
expression on the RHS (mind the -=) we reduce the value modulo
2^width(int) and assign it to entropy_count. Trinity found this.

[ Commit modified by tytso to add an additional safety check for a
  negative entropy_count -- which should never happen, and to also add
  an additional paranoia check to prevent overly large count values to
  be passed into urandom_read().  ]

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
2014-07-19 01:42:13 -04:00
Theodore Ts'o
ee3e00e9e7 random: use registers from interrupted code for CPU's w/o a cycle counter
For CPU's that don't have a cycle counter, or something equivalent
which can be used for random_get_entropy(), random_get_entropy() will
always return 0.  In that case, substitute with the saved interrupt
registers to add a bit more unpredictability.

Some folks have suggested hashing all of the registers
unconditionally, but this would increase the overhead of
add_interrupt_randomness() by at least an order of magnitude, and this
would very likely be unacceptable.

The changes in this commit have been benchmarked as mostly unaffecting
the overhead of add_interrupt_randomness() if the entropy counter is
present, and doubling the overhead if it is not present.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Jörn Engel <joern@logfs.org>
2014-07-15 04:49:41 -04:00
Torsten Duwe
c84dbf61a7 random: add_hwgenerator_randomness() for feeding entropy from devices
This patch adds an interface to the random pool for feeding entropy
in-kernel.

Signed-off-by: Torsten Duwe <duwe@suse.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: H. Peter Anvin <hpa@zytor.com>
2014-07-15 04:49:40 -04:00
Theodore Ts'o
43759d4f42 random: use an improved fast_mix() function
Use more efficient fast_mix() function.  Thanks to George Spelvin for
doing the leg work to find a more efficient mixing function.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
2014-07-15 04:49:40 -04:00
Theodore Ts'o
840f95077f random: clean up interrupt entropy accounting for archs w/o cycle counters
For architectures that don't have cycle counters, the algorithm for
deciding when to avoid giving entropy credit due to back-to-back timer
interrupts didn't make any sense, since we were checking every 64
interrupts.  Change it so that we only give an entropy credit if the
majority of the interrupts are not based on the timer.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
2014-07-15 04:49:39 -04:00
Theodore Ts'o
cff850312c random: only update the last_pulled time if we actually transferred entropy
In xfer_secondary_pull(), check to make sure we need to pull from the
secondary pool before checking and potentially updating the
last_pulled time.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
2014-07-15 04:49:39 -04:00
Theodore Ts'o
85608f8e16 random: remove unneeded hash of a portion of the entropy pool
We previously extracted a portion of the entropy pool in
mix_pool_bytes() and hashed it in to avoid racing CPU's from returning
duplicate random values.  Now that we are using a spinlock to prevent
this from happening, this is no longer necessary.  So remove it, to
simplify the code a bit.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
2014-07-15 04:49:39 -04:00
Theodore Ts'o
91fcb532ef random: always update the entropy pool under the spinlock
Instead of using lockless techniques introduced in commit
902c098a36, use spin_trylock to try to grab entropy pool's lock.  If
we can't get the lock, then just try again on the next interrupt.

Based on discussions with George Spelvin.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
2014-07-15 04:49:39 -04:00
Linus Torvalds
5ee22beeb2 random: fix entropy accounting bug introduced in v3.15
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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness bugfix from Ted Ts'o:
 "random: fix entropy accounting bug introduced in v3.15"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: fix nasty entropy accounting bug
2014-06-17 14:23:14 -10:00
Theodore Ts'o
e33ba5fa7a random: fix nasty entropy accounting bug
Commit 0fb7a01af5 "random: simplify accounting code", introduced in
v3.15, has a very nasty accounting problem when the entropy pool has
has fewer bytes of entropy than the number of requested reserved
bytes.  In that case, "have_bytes - reserved" goes negative, and since
size_t is unsigned, the expression:

       ibytes = min_t(size_t, ibytes, have_bytes - reserved);

... does not do the right thing.  This is rather bad, because it
defeats the catastrophic reseeding feature in the
xfer_secondary_pool() path.

It also can cause the "BUG: spinlock trylock failure on UP" for some
kernel configurations when prandom_reseed() calls get_random_bytes()
in the early init, since when the entropy count gets corrupted,
credit_entropy_bits() erroneously believes that the nonblocking pool
has been fully initialized (when in fact it is not), and so it calls
prandom_reseed(true) recursively leading to the spinlock BUG.

The logic is *not* the same it was originally, but in the cases where
it matters, the behavior is the same, and the resulting code is
hopefully easier to read and understand.

Fixes: 0fb7a01af5 "random: simplify accounting code"
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Greg Price <price@mit.edu>
Cc: stable@vger.kernel.org  #v3.15
2014-06-15 21:04:32 -04:00
Joe Perches
5eb10d912e random: convert use of typedef ctl_table to struct ctl_table
This typedef is unnecessary and should just be removed.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-06 16:08:15 -07:00
Linus Torvalds
681a289548 Merge branch 'for-3.16/core' of git://git.kernel.dk/linux-block into next
Pull block core updates from Jens Axboe:
 "It's a big(ish) round this time, lots of development effort has gone
  into blk-mq in the last 3 months.  Generally we're heading to where
  3.16 will be a feature complete and performant blk-mq.  scsi-mq is
  progressing nicely and will hopefully be in 3.17.  A nvme port is in
  progress, and the Micron pci-e flash driver, mtip32xx, is converted
  and will be sent in with the driver pull request for 3.16.

  This pull request contains:

   - Lots of prep and support patches for scsi-mq have been integrated.
     All from Christoph.

   - API and code cleanups for blk-mq from Christoph.

   - Lots of good corner case and error handling cleanup fixes for
     blk-mq from Ming Lei.

   - A flew of blk-mq updates from me:

     * Provide strict mappings so that the driver can rely on the CPU
       to queue mapping.  This enables optimizations in the driver.

     * Provided a bitmap tagging instead of percpu_ida, which never
       really worked well for blk-mq.  percpu_ida relies on the fact
       that we have a lot more tags available than we really need, it
       fails miserably for cases where we exhaust (or are close to
       exhausting) the tag space.

     * Provide sane support for shared tag maps, as utilized by scsi-mq

     * Various fixes for IO timeouts.

     * API cleanups, and lots of perf tweaks and optimizations.

   - Remove 'buffer' from struct request.  This is ancient code, from
     when requests were always virtually mapped.  Kill it, to reclaim
     some space in struct request.  From me.

   - Remove 'magic' from blk_plug.  Since we store these on the stack
     and since we've never caught any actual bugs with this, lets just
     get rid of it.  From me.

   - Only call part_in_flight() once for IO completion, as includes two
     atomic reads.  Hopefully we'll get a better implementation soon, as
     the part IO stats are now one of the more expensive parts of doing
     IO on blk-mq.  From me.

   - File migration of block code from {mm,fs}/ to block/.  This
     includes bio.c, bio-integrity.c, bounce.c, and ioprio.c.  From me,
     from a discussion on lkml.

  That should describe the meat of the pull request.  Also has various
  little fixes and cleanups from Dave Jones, Shaohua Li, Duan Jiong,
  Fengguang Wu, Fabian Frederick, Randy Dunlap, Robert Elliott, and Sam
  Bradshaw"

* 'for-3.16/core' of git://git.kernel.dk/linux-block: (100 commits)
  blk-mq: push IPI or local end_io decision to __blk_mq_complete_request()
  blk-mq: remember to start timeout handler for direct queue
  block: ensure that the timer is always added
  blk-mq: blk_mq_unregister_hctx() can be static
  blk-mq: make the sysfs mq/ layout reflect current mappings
  blk-mq: blk_mq_tag_to_rq should handle flush request
  block: remove dead code in scsi_ioctl:blk_verify_command
  blk-mq: request initialization optimizations
  block: add queue flag for disabling SG merging
  block: remove 'magic' from struct blk_plug
  blk-mq: remove alloc_hctx and free_hctx methods
  blk-mq: add file comments and update copyright notices
  blk-mq: remove blk_mq_alloc_request_pinned
  blk-mq: do not use blk_mq_alloc_request_pinned in blk_mq_map_request
  blk-mq: remove blk_mq_wait_for_tags
  blk-mq: initialize request in __blk_mq_alloc_request
  blk-mq: merge blk_mq_alloc_reserved_request into blk_mq_alloc_request
  blk-mq: add helper to insert requests from irq context
  blk-mq: remove stale comment for blk_mq_complete_request()
  blk-mq: allow non-softirq completions
  ...
2014-06-02 09:29:34 -07:00
Theodore Ts'o
f9c6d4987b random: fix BUG_ON caused by accounting simplification
Commit ee1de406ba ("random: simplify accounting logic") simplified
things too much, in that it allows the following to trigger an
overflow that results in a BUG_ON crash:

dd if=/dev/urandom of=/dev/zero bs=67108707 count=1

Thanks to Peter Zihlstra for discovering the crash, and Hannes
Frederic for analyizing the root cause.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Greg Price <price@mit.edu>
2014-05-16 22:18:22 -04:00
Christoph Hellwig
bdcfa3e57c random: export add_disk_randomness
This will be needed for pending changes to the scsi midlayer that now
calls lower level block APIs, as well as any blk-mq driver that wants to
contribute to the random pool.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Jens Axboe <axboe@fb.com>
2014-04-28 09:29:55 -06:00
H. Peter Anvin
7b878d4b48 random: Add arch_has_random[_seed]()
Add predicate functions for having arch_get_random[_seed]*().  The
only current use is to avoid the loop in arch_random_refill() when
arch_get_random_seed_long() is unavailable.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2014-03-19 22:24:08 -04:00
H. Peter Anvin
331c6490c7 random: If we have arch_get_random_seed*(), try it before blocking
If we have arch_get_random_seed*(), try to use it for emergency refill
of the entropy pool before giving up and blocking on /dev/random.  It
may or may not work in the moment, but if it does work, it will give
the user better service than blocking will.

Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2014-03-19 22:22:06 -04:00
H. Peter Anvin
83664a6928 random: Use arch_get_random_seed*() at init time and once a second
Use arch_get_random_seed*() in two places in the Linux random
driver (drivers/char/random.c):

1. During entropy pool initialization, use RDSEED in favor of RDRAND,
   with a fallback to the latter.  Entropy exhaustion is unlikely to
   happen there on physical hardware as the machine is single-threaded
   at that point, but could happen in a virtual machine.  In that
   case, the fallback to RDRAND will still provide more than adequate
   entropy pool initialization.

2. Once a second, issue RDSEED and, if successful, feed it to the
   entropy pool.  To ensure an extra layer of security, only credit
   half the entropy just in case.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2014-03-19 22:22:06 -04:00
Theodore Ts'o
46884442fc random: use the architectural HWRNG for the SHA's IV in extract_buf()
To help assuage the fears of those who think the NSA can introduce a
massive hack into the instruction decode and out of order execution
engine in the CPU without hundreds of Intel engineers knowing about
it (only one of which woud need to have the conscience and courage of
Edward Snowden to spill the beans to the public), use the HWRNG to
initialize the SHA starting value, instead of xor'ing it in
afterwards.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:52 -04:00
Greg Price
2132a96f66 random: clarify bits/bytes in wakeup thresholds
These are a recurring cause of confusion, so rename them to
hopefully be clearer.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
7d1b08c40c random: entropy_bytes is actually bits
The variable 'entropy_bytes' is set from an expression that actually
counts bits.  Fortunately it's also only compared to values that also
count bits.  Rename it accordingly.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
0fb7a01af5 random: simplify accounting code
With this we handle "reserved" in just one place.  As a bonus the
code becomes less nested, and the "wakeup_write" flag variable
becomes unnecessary.  The variable "flags" was already unused.

This code behaves identically to the previous version except in
two pathological cases that don't occur.  If the argument "nbytes"
is already less than "min", then we didn't previously enforce
"min".  If r->limit is false while "reserved" is nonzero, then we
previously applied "reserved" in checking whether we had enough
bits, even though we don't apply it to actually limit how many we
take.  The callers of account() never exercise either of these cases.

Before the previous commit, it was possible for "nbytes" to be less
than "min" if userspace chose a pathological configuration, but no
longer.

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
8c2aa3390e random: tighten bound on random_read_wakeup_thresh
We use this value in a few places other than its literal meaning,
in particular in _xfer_secondary_pool() as a minimum number of
bits to pull from the input pool at a time into either output
pool.  It doesn't make sense to pull more bits than the whole size
of an output pool.

We could and possibly should separate the quantities "how much
should the input pool have to have to wake up /dev/random readers"
and "how much should we transfer from the input to an output pool
at a time", but nobody is likely to be sad they can't set the first
quantity to more than 1024 bits, so for now just limit them both.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
a58aa4edc6 random: forget lock in lockless accounting
The only mutable data accessed here is ->entropy_count, but since
10b3a32d2 ("random: fix accounting race condition") we use cmpxchg to
protect our accesses to ->entropy_count here.  Drop the use of the
lock.

Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
ee1de406ba random: simplify accounting logic
This logic is exactly equivalent to the old logic, but it should
be easier to see what it's doing.

The equivalence depends on one fact from outside this function:
when 'r->limit' is false, 'reserved' is zero.  (Well, two facts;
the other is that 'reserved' is never negative.)

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:51 -04:00
Greg Price
19fa5be1d9 random: fix comment on "account"
This comment didn't quite keep up as extract_entropy() was split into
four functions.  Put each bit by the function it describes.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:50 -04:00
Greg Price
12ff3a517a random: simplify loop in random_read
The loop condition never changes until just before a break, so we
might as well write it as a constant.  Also since a996996dd7
("random: drop weird m_time/a_time manipulation") we don't do anything
after the loop finishes, so the 'break's might as well return
directly.  Some other simplifications.

There should be no change in behavior introduced by this commit.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:50 -04:00
Greg Price
18e9cea749 random: fix description of get_random_bytes
After this remark was written, commit d2e7c96af added a use of
arch_get_random_long() inside the get_random_bytes codepath.
The main point stands, but it needs to be reworded.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:50 -04:00
Greg Price
f22052b202 random: fix comment on proc_do_uuid
There's only one function here now, as uuid_strategy is long gone.
Also make the bit about "If accesses via ..." clearer.

Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:50 -04:00
Greg Price
dfd38750db random: fix typos / spelling errors in comments
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2014-03-19 22:18:50 -04:00
Linus Torvalds
0891ad829d The /dev/random changes for 3.13 including a number of improvements in
the following areas: performance, avoiding waste of entropy, better
 tracking of entropy estimates, support for non-x86 platforms that have
 a register which can't be used for fine-grained timekeeping, but which
 might be good enough for the random driver.
 
 Also add some printk's so that we can see how quickly /dev/urandom can
 get initialized, and when programs try to use /dev/urandom before it
 is fully initialized (since this could be a security issue).  This
 shouldn't be an issue on x86 desktop/laptops --- a test on my Lenovo
 T430s laptop shows that /dev/urandom is getting fully initialized
 approximately two seconds before the root file system is mounted
 read/write --- this may be an issue with ARM and MIPS embedded/mobile
 systems, though.  These printk's will be a useful canary before
 potentially adding a future change to start blocking processes which
 try to read from /dev/urandom before it is initialized, which is
 something FreeBSD does already for security reasons, and which
 security folks have been agitating for Linux to also adopt.
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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull /dev/random changes from Ted Ts'o:
 "The /dev/random changes for 3.13 including a number of improvements in
  the following areas: performance, avoiding waste of entropy, better
  tracking of entropy estimates, support for non-x86 platforms that have
  a register which can't be used for fine-grained timekeeping, but which
  might be good enough for the random driver.

  Also add some printk's so that we can see how quickly /dev/urandom can
  get initialized, and when programs try to use /dev/urandom before it
  is fully initialized (since this could be a security issue).  This
  shouldn't be an issue on x86 desktop/laptops --- a test on my Lenovo
  T430s laptop shows that /dev/urandom is getting fully initialized
  approximately two seconds before the root file system is mounted
  read/write --- this may be an issue with ARM and MIPS embedded/mobile
  systems, though.  These printk's will be a useful canary before
  potentially adding a future change to start blocking processes which
  try to read from /dev/urandom before it is initialized, which is
  something FreeBSD does already for security reasons, and which
  security folks have been agitating for Linux to also adopt"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: add debugging code to detect early use of get_random_bytes()
  random: initialize the last_time field in struct timer_rand_state
  random: don't zap entropy count in rand_initialize()
  random: printk notifications for urandom pool initialization
  random: make add_timer_randomness() fill the nonblocking pool first
  random: convert DEBUG_ENT to tracepoints
  random: push extra entropy to the output pools
  random: drop trickle mode
  random: adjust the generator polynomials in the mixing function slightly
  random: speed up the fast_mix function by a factor of four
  random: cap the rate which the /dev/urandom pool gets reseeded
  random: optimize the entropy_store structure
  random: optimize spinlock use in add_device_randomness()
  random: fix the tracepoint for get_random_bytes(_arch)
  random: account for entropy loss due to overwrites
  random: allow fractional bits to be tracked
  random: statically compute poolbitshift, poolbytes, poolbits
  random: mix in architectural randomness earlier in extract_buf()
2013-11-16 10:19:15 -08:00
Hannes Frederic Sowa
4af712e8df random32: add prandom_reseed_late() and call when nonblocking pool becomes initialized
The Tausworthe PRNG is initialized at late_initcall time. At that time the
entropy pool serving get_random_bytes is not filled sufficiently. This
patch adds an additional reseeding step as soon as the nonblocking pool
gets marked as initialized.

On some machines it might be possible that late_initcall gets called after
the pool has been initialized. In this situation we won't reseed again.

(A call to prandom_seed_late blocks later invocations of early reseed
attempts.)

Joint work with Daniel Borkmann.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
2013-11-11 14:32:14 -05:00
Theodore Ts'o
392a546dc8 random: add debugging code to detect early use of get_random_bytes()
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-11-03 18:24:08 -05:00
Theodore Ts'o
644008df89 random: initialize the last_time field in struct timer_rand_state
Since we initialize jiffies to wrap five minutes before boot (see
INITIAL_JIFFIES defined in include/linux/jiffies.h) it's important to
make sure the last_time field is initialized to INITIAL_JIFFIES.
Otherwise, the entropy estimator will overestimate the amount of
entropy resulting from the first call to add_timer_randomness(),
generally by about 8 bits.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-11-03 18:20:05 -05:00
Theodore Ts'o
ae9ecd92dd random: don't zap entropy count in rand_initialize()
The rand_initialize() function was being run fairly late in the kernel
boot sequence.  This was unfortunate, since it zero'ed the entropy
counters, thus throwing away credit that was accumulated earlier in
the boot sequence, and it also meant that initcall functions run
before rand_initialize were using a minimally initialized pool.

To fix this, fix init_std_data() to no longer zap the entropy counter;
it wasn't necessary, and move rand_initialize() to be an early
initcall.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-11-03 18:18:49 -05:00
Theodore Ts'o
301f0595c0 random: printk notifications for urandom pool initialization
Print a notification to the console when the nonblocking pool is
initialized.  Also printk a warning when a process tries reading from
/dev/urandom before it is fully initialized.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-11-03 18:18:48 -05:00
Theodore Ts'o
40db23e533 random: make add_timer_randomness() fill the nonblocking pool first
Change add_timer_randomness() so that it directs incoming entropy to
the nonblocking pool first if it hasn't been fully initialized yet.
This matches the strategy we use in add_interrupt_randomness(), which
allows us to push the randomness where we need it the most during when
the system is first booting up, so that get_random_bytes() and
/dev/urandom become safe to use as soon as possible.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-11-03 18:18:47 -05:00
Linus Torvalds
f715729ee4 These patches are designed to enable improvements to /dev/random for
non-x86 platforms, in particular MIPS and ARM.
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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull /dev/random changes from Ted Ts'o:
 "These patches are designed to enable improvements to /dev/random for
  non-x86 platforms, in particular MIPS and ARM"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: allow architectures to optionally define random_get_entropy()
  random: run random_int_secret_init() run after all late_initcalls
2013-10-10 12:31:43 -07:00
Theodore Ts'o
f80bbd8b92 random: convert DEBUG_ENT to tracepoints
Instead of using the random driver's ad-hoc DEBUG_ENT() mechanism, use
tracepoints instead.  This allows for a much more fine-grained control
of which debugging mechanism which a developer might need, and unifies
the debugging messages with all of the existing tracepoints.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:23 -04:00
Theodore Ts'o
6265e169cd random: push extra entropy to the output pools
As the input pool gets filled, start transfering entropy to the output
pools until they get filled.  This allows us to use the output pools
to store more system entropy.  Waste not, want not....

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:22 -04:00
Theodore Ts'o
95b709b6be random: drop trickle mode
The add_timer_randomness() used to drop into trickle mode when entropy
pool was estimated to be 87.5% full.  This was important when
add_timer_randomness() was used to sample interrupts.  It's not used
for this any more --- add_interrupt_randomness() now uses fast_mix()
instead.  By elimitating trickle mode, it allows us to fully utilize
entropy provided by add_input_randomness() and add_disk_randomness()
even when the input pool is above the old trickle threshold of 87.5%.

This helps to answer the criticism in [1] in their hypothetical
scenario where our entropy estimator was inaccurate, even though the
measurements in [2] seem to indicate that our entropy estimator given
real-life entropy collection is actually pretty good, albeit on the
conservative side (which was as it was designed).

[1] http://eprint.iacr.org/2013/338.pdf
[2] http://eprint.iacr.org/2012/251.pdf

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:21 -04:00
Theodore Ts'o
6e9fa2c8a6 random: adjust the generator polynomials in the mixing function slightly
Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
Videau in their paper, "The Linux Pseudorandom Number Generator
Revisited" (see: http://eprint.iacr.org/2012/251.pdf).

They suggested a slight change to improve our mixing functions
slightly.  I also adjusted the comments to better explain what is
going on, and to document why the polynomials were changed.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:21 -04:00
Theodore Ts'o
655b226470 random: speed up the fast_mix function by a factor of four
By mixing the entropy in chunks of 32-bit words instead of byte by
byte, we can speed up the fast_mix function significantly.  Since it
is called on every single interrupt, on systems with a very heavy
interrupt load, this can make a noticeable difference.

Also fix a compilation warning in add_interrupt_randomness() and avoid
xor'ing cycles and jiffies together just in case we have an
architecture which tries to define random_get_entropy() by returning
jiffies.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Jörn Engel <joern@logfs.org>
2013-10-10 14:32:20 -04:00
Theodore Ts'o
f5c2742c23 random: cap the rate which the /dev/urandom pool gets reseeded
In order to avoid draining the input pool of its entropy at too high
of a rate, enforce a minimum time interval between reseedings of the
urandom pool.  This is set to 60 seconds by default.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:19 -04:00
Theodore Ts'o
c59974aea4 random: optimize the entropy_store structure
Use smaller types to slightly shrink the size of the entropy store
structure.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2013-10-10 14:32:18 -04:00