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CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147)

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Josh Boyer 2012-11-26 09:03:26 -05:00
parent f1e8a77adb
commit fee5e57d00
3 changed files with 274 additions and 1 deletions
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118
exec-do-not-leave-bprm-interp-on-stack.patch Normal file
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@ -0,0 +1,118 @@
From 6752ab4cb863fc63ed85f1ca78a42235c09fad83 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Mon, 26 Nov 2012 09:07:50 -0500
Subject: [PATCH 1/2] exec: do not leave bprm->interp on stack
If a series of scripts are executed, each triggering module loading via
unprintable bytes in the script header, kernel stack contents can leak
into the command line.
Normally execution of binfmt_script and binfmt_misc happens recursively.
However, when modules are enabled, and unprintable bytes exist in the
bprm->buf, execution will restart after attempting to load matching binfmt
modules. Unfortunately, the logic in binfmt_script and binfmt_misc does
not expect to get restarted. They leave bprm->interp pointing to their
local stack. This means on restart bprm->interp is left pointing into
unused stack memory which can then be copied into the userspace argv
areas.
After additional study, it seems that both recursion and restart remains
the desirable way to handle exec with scripts, misc, and modules. As
such, we need to protect the changes to interp.
This changes the logic to require allocation for any changes to the
bprm->interp. To avoid adding a new kmalloc to every exec, the default
value is left as-is. Only when passing through binfmt_script or
binfmt_misc does an allocation take place.
For a proof of concept, see DoTest.sh from:
http://www.halfdog.net/Security/2012/LinuxKernelBinfmtScriptStackDataDisclosure/
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: halfdog <me@halfdog.net>
Cc: P J P <ppandit@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/binfmt_misc.c | 5 ++++-
fs/binfmt_script.c | 4 +++-
fs/exec.c | 15 +++++++++++++++
include/linux/binfmts.h | 1 +
4 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 790b3cd..772428d 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -176,7 +176,10 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
goto _error;
bprm->argc ++;
- bprm->interp = iname; /* for binfmt_script */
+ /* Update interp in case binfmt_script needs it. */
+ retval = bprm_change_interp(iname, bprm);
+ if (retval < 0)
+ goto _error;
interp_file = open_exec (iname);
retval = PTR_ERR (interp_file);
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index d3b8c1f..df49d48 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -82,7 +82,9 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
retval = copy_strings_kernel(1, &i_name, bprm);
if (retval) return retval;
bprm->argc++;
- bprm->interp = interp;
+ retval = bprm_change_interp(interp, bprm);
+ if (retval < 0)
+ return retval;
/*
* OK, now restart the process with the interpreter's dentry.
diff --git a/fs/exec.c b/fs/exec.c
index 0039055..c6e6de4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1175,9 +1175,24 @@ void free_bprm(struct linux_binprm *bprm)
mutex_unlock(&current->signal->cred_guard_mutex);
abort_creds(bprm->cred);
}
+ /* If a binfmt changed the interp, free it. */
+ if (bprm->interp != bprm->filename)
+ kfree(bprm->interp);
kfree(bprm);
}
+int bprm_change_interp(char *interp, struct linux_binprm *bprm)
+{
+ /* If a binfmt changed the interp, free it first. */
+ if (bprm->interp != bprm->filename)
+ kfree(bprm->interp);
+ bprm->interp = kstrdup(interp, GFP_KERNEL);
+ if (!bprm->interp)
+ return -ENOMEM;
+ return 0;
+}
+EXPORT_SYMBOL(bprm_change_interp);
+
/*
* install the new credentials for this executable
*/
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index cfcc6bf..de0628e 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -114,6 +114,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm,
unsigned long stack_top,
int executable_stack);
extern int bprm_mm_init(struct linux_binprm *bprm);
+extern int bprm_change_interp(char *interp, struct linux_binprm *bprm);
extern int copy_strings_kernel(int argc, const char *const *argv,
struct linux_binprm *bprm);
extern int prepare_bprm_creds(struct linux_binprm *bprm);
--
1.8.0

144
exec-use-eloop-for-max-recursion-depth.patch Normal file
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@ -0,0 +1,144 @@
From ba1b23d05259e31d30a78017cdfbc010dcb08aa6 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Mon, 26 Nov 2012 09:02:11 -0500
Subject: [PATCH 2/2] exec: use -ELOOP for max recursion depth
To avoid an explosion of request_module calls on a chain of abusive
scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
as maximum recursion depth is hit, the error will fail all the way back
up the chain, aborting immediately.
This also has the side-effect of stopping the user's shell from attempting
to reexecute the top-level file as a shell script. As seen in the
dash source:
if (cmd != path_bshell && errno == ENOEXEC) {
*argv-- = cmd;
*argv = cmd = path_bshell;
goto repeat;
}
The above logic was designed for running scripts automatically that lacked
the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
things continue to behave as the shell expects.
Additionally, when tracking recursion, the binfmt handlers should not be
involved. The recursion being tracked is the depth of calls through
search_binary_handler(), so that function should be exclusively responsible
for tracking the depth.
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: halfdog <me@halfdog.net>
Cc: P J P <ppandit@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/binfmt_em86.c | 1 -
fs/binfmt_misc.c | 6 ------
fs/binfmt_script.c | 4 +---
fs/exec.c | 10 +++++-----
include/linux/binfmts.h | 2 --
5 files changed, 6 insertions(+), 17 deletions(-)
diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c
index 2790c7e..575796a 100644
--- a/fs/binfmt_em86.c
+++ b/fs/binfmt_em86.c
@@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs)
return -ENOEXEC;
}
- bprm->recursion_depth++; /* Well, the bang-shell is implicit... */
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 772428d..f0f1a06 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -117,10 +117,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
if (!enabled)
goto _ret;
- retval = -ENOEXEC;
- if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
- goto _ret;
-
/* to keep locking time low, we copy the interpreter string */
read_lock(&entries_lock);
fmt = check_file(bprm);
@@ -200,8 +196,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
if (retval < 0)
goto _error;
- bprm->recursion_depth++;
-
retval = search_binary_handler (bprm, regs);
if (retval < 0)
goto _error;
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index df49d48..8ae4be1 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -22,15 +22,13 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
char interp[BINPRM_BUF_SIZE];
int retval;
- if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') ||
- (bprm->recursion_depth > BINPRM_MAX_RECURSION))
+ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
return -ENOEXEC;
/*
* This section does the #! interpretation.
* Sorta complicated, but hopefully it will work. -TYT
*/
- bprm->recursion_depth++;
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/fs/exec.c b/fs/exec.c
index c6e6de4..85c1f9e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1371,6 +1371,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
struct linux_binfmt *fmt;
pid_t old_pid, old_vpid;
+ /* This allows 4 levels of binfmt rewrites before failing hard. */
+ if (depth > 5)
+ return -ELOOP;
+
retval = security_bprm_check(bprm);
if (retval)
return retval;
@@ -1395,12 +1399,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
if (!try_module_get(fmt->module))
continue;
read_unlock(&binfmt_lock);
+ bprm->recursion_depth = depth + 1;
retval = fn(bprm, regs);
- /*
- * Restore the depth counter to its starting value
- * in this call, so we don't have to rely on every
- * load_binary function to restore it on return.
- */
bprm->recursion_depth = depth;
if (retval >= 0) {
if (depth == 0) {
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index de0628e..54135f6 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -54,8 +54,6 @@ struct linux_binprm {
#define BINPRM_FLAGS_EXECFD_BIT 1
#define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT)
-#define BINPRM_MAX_RECURSION 4
-
/* Function parameter for binfmt->coredump */
struct coredump_params {
siginfo_t *siginfo;
--
1.8.0

13
kernel.spec
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@ -62,7 +62,7 @@ Summary: The Linux kernel
# For non-released -rc kernels, this will be appended after the rcX and
# gitX tags, so a 3 here would become part of release "0.rcX.gitX.3"
#
%global baserelease 1
%global baserelease 2
%global fedora_build %{baserelease}
# base_sublevel is the kernel version we're starting with and patching
@ -773,6 +773,10 @@ Patch22125: Bluetooth-Add-support-for-BCM20702A0.patch
#rhbz 859485
Patch21226: vt-Drop-K_OFF-for-VC_MUTE.patch
#rhbz CVE-2012-4530 868285 880147
Patch21228: exec-do-not-leave-bprm-interp-on-stack.patch
Patch21229: exec-use-eloop-for-max-recursion-depth.patch
# END OF PATCH DEFINITIONS
%endif
@ -1486,6 +1490,10 @@ ApplyPatch Bluetooth-Add-support-for-BCM20702A0.patch
#rhbz 859485
ApplyPatch vt-Drop-K_OFF-for-VC_MUTE.patch
#rhbz CVE-2012-4530 868285 880147
ApplyPatch exec-do-not-leave-bprm-interp-on-stack.patch
ApplyPatch exec-use-eloop-for-max-recursion-depth.patch
# END OF PATCH APPLICATIONS
%endif
@ -2353,6 +2361,9 @@ fi
# ||----w |
# || ||
%changelog
* Mon Nov 26 2012 Josh Boyer <jwboyer@redhat.com>
- CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147)
* Sun Nov 25 2012 Josh Boyer <jwboyer@redhat.com> - 3.7.0-0.rc6.git4.1
- Linux v3.7-rc6-209-g194d983