From e9c6a182649f4259db704ae15a91ac820e63b0ca Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Wed, 16 Oct 2013 03:17:47 +0100 Subject: [PATCH] dm snapshot: fix data corruption This patch fixes a particular type of data corruption that has been encountered when loading a snapshot's metadata from disk. When we allocate a new chunk in persistent_prepare, we increment ps->next_free and we make sure that it doesn't point to a metadata area by further incrementing it if necessary. When we load metadata from disk on device activation, ps->next_free is positioned after the last used data chunk. However, if this last used data chunk is followed by a metadata area, ps->next_free is positioned erroneously to the metadata area. A newly-allocated chunk is placed at the same location as the metadata area, resulting in data or metadata corruption. This patch changes the code so that ps->next_free skips the metadata area when metadata are loaded in function read_exceptions. The patch also moves a piece of code from persistent_prepare_exception to a separate function skip_metadata to avoid code duplication. CVE-2013-4299 Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org Cc: Mike Snitzer Signed-off-by: Alasdair G Kergon --- drivers/md/dm-snap-persistent.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c index 4caa8e6d59d7..2d2b1b7588d7 100644 --- a/drivers/md/dm-snap-persistent.c +++ b/drivers/md/dm-snap-persistent.c @@ -269,6 +269,14 @@ static chunk_t area_location(struct pstore *ps, chunk_t area) return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area); } +static void skip_metadata(struct pstore *ps) +{ + uint32_t stride = ps->exceptions_per_area + 1; + chunk_t next_free = ps->next_free; + if (sector_div(next_free, stride) == NUM_SNAPSHOT_HDR_CHUNKS) + ps->next_free++; +} + /* * Read or write a metadata area. Remembering to skip the first * chunk which holds the header. @@ -502,6 +510,8 @@ static int read_exceptions(struct pstore *ps, ps->current_area--; + skip_metadata(ps); + return 0; } @@ -616,8 +626,6 @@ static int persistent_prepare_exception(struct dm_exception_store *store, struct dm_exception *e) { struct pstore *ps = get_info(store); - uint32_t stride; - chunk_t next_free; sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev); /* Is there enough room ? */ @@ -630,10 +638,8 @@ static int persistent_prepare_exception(struct dm_exception_store *store, * Move onto the next free pending, making sure to take * into account the location of the metadata chunks. */ - stride = (ps->exceptions_per_area + 1); - next_free = ++ps->next_free; - if (sector_div(next_free, stride) == 1) - ps->next_free++; + ps->next_free++; + skip_metadata(ps); atomic_inc(&ps->pending_count); return 0; -- 2.20.1