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authorMikulas Patocka <mpatocka@redhat.com>2013-10-16 06:17:47 +0400
committerAlasdair G Kergon <agk@redhat.com>2013-10-16 06:17:47 +0400
commite9c6a182649f4259db704ae15a91ac820e63b0ca (patch)
tree3cfbfc80ce16f6655a8eb823015bd2f34df87dc1 /drivers/md/dm-snap-persistent.c
parent61e6cfa80de5760bbe406f4e815b7739205754d2 (diff)
downloadlinux-e9c6a182649f4259db704ae15a91ac820e63b0ca.tar.xz
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 <mpatocka@redhat.com> Cc: stable@vger.kernel.org Cc: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm-snap-persistent.c')
-rw-r--r--drivers/md/dm-snap-persistent.c18
1 files 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;