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CVE-2011-2183: ksm: race between ksmd and exiting task

This commit is contained in:
Chuck Ebbert 2011-06-24 06:12:52 -04:00
parent 7562ee4726
commit ced86e1611
2 changed files with 90 additions and 0 deletions
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8
kernel.spec
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@ -619,6 +619,9 @@ Patch30: linux-2.6-tracehook.patch
Patch31: linux-2.6-utrace.patch
Patch32: linux-2.6-utrace-ptrace.patch
# CVE-2011-2183
Patch80: ksm-fix-null-pointer-dereference-in-scan-get-next-rmap-item.patch
Patch150: linux-2.6.29-sparc-IOC_TYPECHECK.patch
Patch160: linux-2.6-32bit-mmap-exec-randomization.patch
@ -1210,6 +1213,10 @@ ApplyPatch linux-2.6-tracehook.patch
ApplyPatch linux-2.6-utrace.patch
ApplyPatch linux-2.6-utrace-ptrace.patch
# mm patches
# CVE-2011-2183
ApplyPatch ksm-fix-null-pointer-dereference-in-scan-get-next-rmap-item.patch
# Architecture patches
# x86(-64)
# Restore reliable stack backtraces, and hopefully
@ -2037,6 +2044,7 @@ fi
- block-blkdev_get-should-access-bd_disk-only-after.patch:
fix potential oops introduced in 2.6.38.8
- ahci-add-another-pci-id-for-marvell.patch (#705960)
- CVE-2011-2183: ksm: race between ksmd and exiting task
* Thu Jun 23 2011 Dave Airlie <airlied@redhat.com> 2.6.38.8-34
- drm-i915-snb-irq-stalls-fix.patch: fix Sandybridge IRQ stalls

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ksm-fix-null-pointer-dereference-in-scan-get-next-rmap-item.patch Normal file
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@ -0,0 +1,82 @@
From: Hugh Dickins <hughd@google.com>
Date: Wed, 15 Jun 2011 22:08:58 +0000 (-0700)
Subject: ksm: fix NULL pointer dereference in scan_get_next_rmap_item()
X-Git-Tag: v3.0-rc4~44
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=2b472611a32a72f4a118c069c2d62a1a3f087afd
ksm: fix NULL pointer dereference in scan_get_next_rmap_item()
Andrea Righi reported a case where an exiting task can race against
ksmd::scan_get_next_rmap_item (http://lkml.org/lkml/2011/6/1/742) easily
triggering a NULL pointer dereference in ksmd.
ksm_scan.mm_slot == &ksm_mm_head with only one registered mm
CPU 1 (__ksm_exit) CPU 2 (scan_get_next_rmap_item)
list_empty() is false
lock slot == &ksm_mm_head
list_del(slot->mm_list)
(list now empty)
unlock
lock
slot = list_entry(slot->mm_list.next)
(list is empty, so slot is still ksm_mm_head)
unlock
slot->mm == NULL ... Oops
Close this race by revalidating that the new slot is not simply the list
head again.
Andrea's test case:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#define BUFSIZE getpagesize()
int main(int argc, char **argv)
{
void *ptr;
if (posix_memalign(&ptr, getpagesize(), BUFSIZE) < 0) {
perror("posix_memalign");
exit(1);
}
if (madvise(ptr, BUFSIZE, MADV_MERGEABLE) < 0) {
perror("madvise");
exit(1);
}
*(char *)NULL = 0;
return 0;
}
Reported-by: Andrea Righi <andrea@betterlinux.com>
Tested-by: Andrea Righi <andrea@betterlinux.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
diff --git a/mm/ksm.c b/mm/ksm.c
index d708b3e..9a68b0c 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1302,6 +1302,12 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
ksm_scan.mm_slot = slot;
spin_unlock(&ksm_mmlist_lock);
+ /*
+ * Although we tested list_empty() above, a racing __ksm_exit
+ * of the last mm on the list may have removed it since then.
+ */
+ if (slot == &ksm_mm_head)
+ return NULL;
next_mm:
ksm_scan.address = 0;
ksm_scan.rmap_list = &slot->rmap_list;