[PATCH 7.2.y] dm-pcache: bound the logical key offset from persistent memory

[Sasha Levin <sashal@kernel.org>]

From: Bryam Vargas <hexlabsecurity@proton.me>

[ Upstream commit 97fc4b53dbe4a983fdf093243067fa6a64562307 ]

cache_key_decode() takes a key's logical off from the cache device and
later indexes req_key_tree->subtrees[] by it in get_subtree(). An off
past the device forms a subtree pointer outside the array, which
rb_insert() writes through during replay.

Reject a key of zero length, or whose off+len (computed in 64 bits)
exceeds the device size, before it is used.

Fixes: 1d57628ff95b ("dm-pcache: add persistent cache target in device-mapper")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
[ adjusted context to account for the missing cache_seg_id_valid() check. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-pcache/cache_key.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/md/dm-pcache/cache_key.c b/drivers/md/dm-pcache/cache_key.c
index 51dd1ccf4e2fd..c98005d16fd6b 100644
--- a/drivers/md/dm-pcache/cache_key.c
+++ b/drivers/md/dm-pcache/cache_key.c
@@ -90,10 +90,19 @@ int cache_key_decode(struct pcache_cache *cache,
 			struct pcache_cache_key *key)
 {
 	struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
+	u64 dev_bytes = (u64)cache->dev_size << SECTOR_SHIFT;
 
 	key->off = key_onmedia->off;
 	key->len = key_onmedia->len;
 
+	if (key_onmedia->len == 0 ||
+	    key_onmedia->len > dev_bytes ||
+	    key_onmedia->off > dev_bytes - key_onmedia->len) {
+		pcache_dev_err(pcache, "key off %llu + len %u exceeds device size\n",
+				key_onmedia->off, key_onmedia->len);
+		return -EIO;
+	}
+
 	key->cache_pos.cache_seg = &cache->segments[key_onmedia->cache_seg_id];
 	key->cache_pos.seg_off = key_onmedia->cache_seg_off;
 
-- 
2.53.0