[PATCH 4.4 09/31] dm snapshot: fix a crash when an origin has no snapshots

Greg Kroah-Hartman
2021-05-24T15:34:55Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 7ee06ddc4038f936b0d4459d37a7d4d844fb03db upstream.

If an origin target has no snapshots, o->split_boundary is set to 0.
This causes BUG_ON(sectors <= 0) in block/bio.c:bio_split().

Fix this by initializing chunk_size, and in turn split_boundary, to
rounddown_pow_of_two(UINT_MAX) -- the largest power of two that fits
into "unsigned" type.

Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Tested-by: Michael Tokarev <mjt@tls.msk.ru>
Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-snap.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -789,12 +789,11 @@ static int dm_add_exception(void *contex
static uint32_t __minimum_chunk_size(struct origin *o)
{
struct dm_snapshot *snap;
- unsigned chunk_size = 0;
+ unsigned chunk_size = rounddown_pow_of_two(UINT_MAX);

if (o)
list_for_each_entry(snap, &o->snapshots, list)
- chunk_size = min_not_zero(chunk_size,
- snap->store->chunk_size);
+ chunk_size = min(chunk_size, snap->store->chunk_size);

return (uint32_t) chunk_size;
}