When dm_bm_read_lock() fails due to locking or checksum errors, it
releases the faulty block implicitly while leaving an invalid output
pointer behind. The caller of dm_bm_read_lock() should not operate on
this invalid dm_block pointer, or it will lead to undefined result.
For example, the dm_array_cursor incorrectly caches the invalid pointer
on reading a faulty array block, causing a double release in
dm_array_cursor_end(), then hitting the BUG_ON in dm-bufio cache_put().
Reproduce steps:
1. initialize a cache device
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"
dmsetup create corig --table "0 524288 linear /dev/sdc $262144"
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1
dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
2. wipe the second array block offline
dmsteup remove cache cmeta cdata corig
mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192 \
2>/dev/null | hexdump -e '1/8 "%u\n"')
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056)) \
2>/dev/null | hexdump -e '1/8 "%u\n"')
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock
3. try reopen the cache device
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"
dmsetup create corig --table "0 524288 linear /dev/sdc $262144"
dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
Kernel logs:
(snip)
device-mapper: array: array_block_check failed: blocknr 0 != wanted 10
device-mapper: block manager: array validator check failed for block 10
device-mapper: array: get_ablock failed
device-mapper: cache metadata: dm_array_cursor_next for mapping failed
------------[ cut here ]------------
kernel BUG at drivers/md/dm-bufio.c:638!
Fix by setting the cached block pointer to NULL on errors.
Signed-off-by: Ming-Hung Tsai <mtsai@xxxxxxxxxx>
Fixes: fdd1315aa5f0 ("dm array: introduce cursor api")
---
drivers/md/persistent-data/dm-array.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/md/persistent-data/dm-array.c b/drivers/md/persistent-data/dm-array.c
index 157c9bd2fed7..c46a374f7459 100644
--- a/drivers/md/persistent-data/dm-array.c
+++ b/drivers/md/persistent-data/dm-array.c
@@ -917,23 +917,28 @@ static int load_ablock(struct dm_array_cursor *c)
if (c->block)
unlock_ablock(c->info, c->block);
- c->block = NULL;
- c->ab = NULL;
c->index = 0;
r = dm_btree_cursor_get_value(&c->cursor, &key, &value_le);
if (r) {
DMERR("dm_btree_cursor_get_value failed");
dm_btree_cursor_end(&c->cursor);
+ goto out;
} else {
r = get_ablock(c->info, le64_to_cpu(value_le), &c->block, &c->ab);
if (r) {
DMERR("get_ablock failed");
dm_btree_cursor_end(&c->cursor);
+ goto out;
}
}
+ return 0;
+
+out:
+ c->block = NULL;
+ c->ab = NULL;
return r;
}
--
2.47.0
