From: Mikulas Patocka Date: Mon, 21 Oct 2013 11:59:30 +0000 (+0100) Subject: dm snapshot: fix data corruption X-Git-Tag: v2.6.32.62~13 X-Git-Url: https://git.fsl.cs.sunysb.edu/?a=commitdiff_plain;h=1b3b362f84f5f2dd62d180447ba1a1681f5d993a;p=unionfs-2.6.39.y.git dm snapshot: fix data corruption CVE-2013-4299 BugLink: http://bugs.launchpad.net/bugs/1241769 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 (back ported from commit e9c6a182649f4259db704ae15a91ac820e63b0ca) Signed-off-by: Luis Henriques Acked-by: Stefan Bader Signed-off-by: Tim Gardner Signed-off-by: Willy Tarreau --- diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c index 0c746420c00..97c3f0651c4 100644 --- a/drivers/md/dm-snap-persistent.c +++ b/drivers/md/dm-snap-persistent.c @@ -252,6 +252,14 @@ static chunk_t area_location(struct pstore *ps, chunk_t area) return 1 + ((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) == 1) + ps->next_free++; +} + /* * Read or write a metadata area. Remembering to skip the first * chunk which holds the header. @@ -481,6 +489,8 @@ static int read_exceptions(struct pstore *ps, ps->current_area--; + skip_metadata(ps); + return 0; } @@ -587,8 +597,6 @@ static int persistent_prepare_exception(struct dm_exception_store *store, struct dm_snap_exception *e) { struct pstore *ps = get_info(store); - uint32_t stride; - chunk_t next_free; sector_t size = get_dev_size(store->cow->bdev); /* Is there enough room ? */ @@ -601,10 +609,8 @@ 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;