This is a note to let you know that I've just added the patch titled
ksm: fix NULL pointer dereference in
to the 2.6.32-longterm tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/longterm/longterm-queue-2.6.32.git;a=summary
The filename of the patch is:
ksm-fix-null-pointer-dereference-in.patch
and it can be found in the queue-2.6.32 subdirectory.
If you, or anyone else, feels it should not be added to the 2.6.32 longterm
tree,
please let <sta...@kernel.org> know about it.
>From 2b472611a32a72f4a118c069c2d62a1a3f087afd Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hu...@google.com>
Date: Wed, 15 Jun 2011 15:08:58 -0700
Subject: ksm: fix NULL pointer dereference in
scan_get_next_rmap_item()
From: Hugh Dickins <hu...@google.com>
commit 2b472611a32a72f4a118c069c2d62a1a3f087afd upstream.
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 <and...@betterlinux.com>
Tested-by: Andrea Righi <and...@betterlinux.com>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Signed-off-by: Hugh Dickins <hu...@google.com>
Signed-off-by: Chris Wright <chr...@sous-sol.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@suse.de>
---
mm/ksm.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1215,6 +1215,12 @@ static struct rmap_item *scan_get_next_r
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_item = list_entry(&slot->rmap_list,
Patches currently in longterm-queue-2.6.32 which might be from hu...@google.com
are
/home/gregkh/linux/longterm/longterm-queue-2.6.32/queue-2.6.32/ksm-fix-null-pointer-dereference-in.patch
/home/gregkh/linux/longterm/longterm-queue-2.6.32/queue-2.6.32/migrate-don-t-account-swapcache-as-shmem.patch
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