[PATCH v2 04/11] dm-pcache: bound the persisted tail-position offset

[Bryam Vargas via B4 Relay <devnull+hexlabsecurity.proton.me@kernel.org>]

From: Bryam Vargas <hexlabsecurity@proton.me>

cache_pos_decode() takes the persisted key_tail and dirty_tail seg_off from
the cache device and addresses within the segment with it. A seg_off at or
past the segment data_size, controllable by whoever supplies the device
(CAP_SYS_ADMIN), reads past the segment data.

Reject a decoded seg_off that is not below the segment data_size.

Fixes: 1d57628ff95b ("dm-pcache: add persistent cache target in device-mapper")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
---
 drivers/md/dm-pcache/cache.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
index e4784578b9af..a94eadb7affd 100644
--- a/drivers/md/dm-pcache/cache.c
+++ b/drivers/md/dm-pcache/cache.c
@@ -122,6 +122,10 @@ int cache_pos_decode(struct pcache_cache *cache,
 		return -EIO;
 
 	pos->cache_seg = &cache->segments[latest.cache_seg_id];
+
+	if (latest.seg_off >= pos->cache_seg->segment.data_size)
+		return -EIO;
+
 	pos->seg_off = latest.seg_off;
 	*seq = latest.header.seq;
 	*index = (latest_addr - pos_onmedia);

-- 
2.43.0