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dm-pcache: fix use-after-free and invalid seg operations in kset_replay()

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In kset_replay, when key->seg_gen is stale (key->seg_gen <
key->cache_pos.cache_seg->gen), cache_key_put(key) is called but then
key->cache_pos.cache_seg is accessed as the argument to cache_seg_get().
This is a use-after-free on the freed key memory. Although mempool
recycled memory is not immediately reclaimed or overwritten in practice,
this is still a potential UAF bug.

Additionally, for expired invalid keys, setting the cache->seg_map bit
and calling cache_seg_get() is unreasonable since the corresponding
segment data is no longer valid.

Fix both issues by moving cache_seg_get() and __set_bit() after the
gen check, so they only execute for valid keys, and using continue to
skip invalid keys.

Cc: stable@vger.kernel.org
Fixes: 1d57628ff9 ("dm-pcache: add persistent cache target in device-mapper")
Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Jianyun Gao 2026-07-20 11:36:32 +08:00 committed by Mikulas Patocka
parent fb9e17287a
commit c2e894eac3
1 changed files with 6 additions and 7 deletions
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13
drivers/md/dm-pcache/cache_key.c
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@ -751,18 +751,17 @@ static int kset_replay(struct pcache_cache *cache, struct pcache_cache_kset_onme
goto err;
}
__set_bit(key->cache_pos.cache_seg->cache_seg_id, cache->seg_map);
/* Check if the segment generation is valid for insertion. */
if (key->seg_gen < key->cache_pos.cache_seg->gen) {
cache_key_put(key);
} else {
cache_subtree = get_subtree(&cache->req_key_tree, key->off);
spin_lock(&cache_subtree->tree_lock);
cache_key_insert(&cache->req_key_tree, key, true);
spin_unlock(&cache_subtree->tree_lock);
continue;
}
__set_bit(key->cache_pos.cache_seg->cache_seg_id, cache->seg_map);
cache_subtree = get_subtree(&cache->req_key_tree, key->off);
spin_lock(&cache_subtree->tree_lock);
cache_key_insert(&cache->req_key_tree, key, true);
spin_unlock(&cache_subtree->tree_lock);
cache_seg_get(key->cache_pos.cache_seg);
}