This is a note to let you know that I've just added the patch titled
dm snapshot: fix data corruption
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-snapshot-fix-data-corruption.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e9c6a182649f4259db704ae15a91ac820e63b0ca Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Wed, 16 Oct 2013 03:17:47 +0100
Subject: dm snapshot: fix data corruption
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
commit e9c6a182649f4259db704ae15a91ac820e63b0ca upstream.
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@xxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-snap-persistent.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -269,6 +269,14 @@ static chunk_t area_location(struct psto
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->current_area--;
+ skip_metadata(ps);
+
return 0;
}
@@ -616,8 +626,6 @@ static int persistent_prepare_exception(
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(
* 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;
Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are
queue-3.4/dm-snapshot-fix-data-corruption.patch
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