dm snapshot: fix on disk chunk size validation

Fix some problems seen in the chunk size processing when activating a
pre-existing snapshot.

For a new snapshot, the chunk size can either be supplied by the creator
or a default value can be used.  For an existing snapshot, the
chunk size in the snapshot header on disk should always be used.

If someone attempts to load an existing snapshot and has the 'default
chunk size' option set, the kernel uses its default value even when it
is incorrect for the snapshot being loaded.  This patch ensures the
correct on-disk value is always used.

Secondly, when the code does use the chunk size stored on the disk it is
prudent to revalidate it, so the code can exit cleanly if it got
corrupted as happened in
https://bugzilla.redhat.com/show_bug.cgi?id=461506 .

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index 4c01c7535fb5..556acff3952f 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -191,6 +191,11 @@ int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
                 return -EINVAL;
         }
 
+        if (chunk_size_ulong > INT_MAX >> SECTOR_SHIFT) {
+                *error = "Chunk size is too high";
+                return -EINVAL;
+        }
+
         store->chunk_size = chunk_size_ulong;
         store->chunk_mask = chunk_size_ulong - 1;
         store->chunk_shift = ffs(chunk_size_ulong) - 1;