| From | lizf@kernel ... | Subject | [PATCH 3.4 044/172] dm snapshot: fix a possible invalid memory access on unload | Date | Tue, 16 Jun 2015 16:34:58 +0800 |
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From: Mikulas Patocka <mpatocka@redhat.com>
3.4.108-rc1 review patch. If anyone has any objections, please let me know.
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commit 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3 upstream.
When the snapshot target is unloaded, snapshot_dtr() waits until pending_exceptions_count drops to zero. Then, it destroys the snapshot. Therefore, the function that decrements pending_exceptions_count should not touch the snapshot structure after the decrement.
pending_complete() calls free_pending_exception(), which decrements pending_exceptions_count, and then it performs up_write(&s->lock) and it calls retry_origin_bios() which dereferences s->origin. These two memory accesses to the fields of the snapshot may touch the dm_snapshot struture after it is freed.
This patch moves the call to free_pending_exception() to the end of pending_complete(), so that the snapshot will not be destroyed while pending_complete() is in progress.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Zefan Li <lizefan@huawei.com> --- drivers/md/dm-snap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index b092338..696a16b 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1444,8 +1444,6 @@ out: full_bio->bi_end_io = pe->full_bio_end_io; full_bio->bi_private = pe->full_bio_private; } - free_pending_exception(pe); - increment_pending_exceptions_done_count(); up_write(&s->lock); @@ -1462,6 +1460,8 @@ out: } retry_origin_bios(s, origin_bios); + + free_pending_exception(pe); } static void commit_callback(void *context, int success) -- 1.9.1
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