[PATCH 7.2.y] dm-pcache: reject a kset that overruns its segment

[Sasha Levin <sashal@kernel.org>]

From: Bryam Vargas <hexlabsecurity@proton.me>

[ Upstream commit 7ac1f10f987a2ffae4aecf0e2ceca8f552b665cb ]

cache_replay(), the writeback worker and the GC worker read a kset of
get_kset_onmedia_size() bytes and advance the position by it. A forged
key_num makes that size exceed the segment's remaining space, so the
advance walks past the segment and trips the cache_pos_advance() BUG_ON.

Reject a kset whose on-media size exceeds cache_seg_remain() before use.

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>
[ backported missing writeback_errors support from the upstream dependency. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-pcache/cache.h           | 1 +
 drivers/md/dm-pcache/cache_gc.c        | 5 +++++
 drivers/md/dm-pcache/cache_key.c       | 5 +++++
 drivers/md/dm-pcache/cache_writeback.c | 8 ++++++++
 4 files changed, 19 insertions(+)

diff --git a/drivers/md/dm-pcache/cache.h b/drivers/md/dm-pcache/cache.h
index afc112b79496a..93c1e699a3944 100644
--- a/drivers/md/dm-pcache/cache.h
+++ b/drivers/md/dm-pcache/cache.h
@@ -180,6 +180,7 @@ struct pcache_cache {
 		u32 advance;
 		int ret;
 	} writeback_ctx;
+	atomic_t		writeback_errors;
 
 	char gc_kset_onmedia_buf[PCACHE_KSET_ONMEDIA_SIZE_MAX];
 	struct delayed_work	gc_work;
diff --git a/drivers/md/dm-pcache/cache_gc.c b/drivers/md/dm-pcache/cache_gc.c
index 3088cfef951bc..99999a92c4e67 100644
--- a/drivers/md/dm-pcache/cache_gc.c
+++ b/drivers/md/dm-pcache/cache_gc.c
@@ -134,6 +134,11 @@ void pcache_cache_gc_fn(struct work_struct *work)
 			continue;
 		}
 
+		if (get_kset_onmedia_size(kset_onmedia) > cache_seg_remain(&key_tail)) {
+			atomic_inc(&cache->gc_errors);
+			return;
+		}
+
 		for (i = 0; i < kset_onmedia->key_num; i++) {
 			struct pcache_cache_key key_tmp = { 0 };
 
diff --git a/drivers/md/dm-pcache/cache_key.c b/drivers/md/dm-pcache/cache_key.c
index 51dd1ccf4e2fd..93933651d2c96 100644
--- a/drivers/md/dm-pcache/cache_key.c
+++ b/drivers/md/dm-pcache/cache_key.c
@@ -811,6 +811,11 @@ int cache_replay(struct pcache_cache *cache)
 		}
 
 		/* Replay the kset and check for errors. */
+		if (get_kset_onmedia_size(kset_onmedia) > cache_seg_remain(pos)) {
+			ret = -EIO;
+			goto out;
+		}
+
 		ret = kset_replay(cache, kset_onmedia);
 		if (ret)
 			goto out;
diff --git a/drivers/md/dm-pcache/cache_writeback.c b/drivers/md/dm-pcache/cache_writeback.c
index 3df8687e2382f..656e4d0489121 100644
--- a/drivers/md/dm-pcache/cache_writeback.c
+++ b/drivers/md/dm-pcache/cache_writeback.c
@@ -229,6 +229,9 @@ void cache_writeback_fn(struct work_struct *work)
 	if (pcache_is_stopping(pcache))
 		goto unlock;
 
+	if (atomic_read(&cache->writeback_errors))
+		goto unlock;
+
 	kset_onmedia = (struct pcache_cache_kset_onmedia *)cache->wb_kset_onmedia_buf;
 
 	mutex_lock(&cache->dirty_tail_lock);
@@ -246,6 +249,11 @@ void cache_writeback_fn(struct work_struct *work)
 		goto queue_work;
 	}
 
+	if (get_kset_onmedia_size(kset_onmedia) > cache_seg_remain(&dirty_tail)) {
+		atomic_inc(&cache->writeback_errors);
+		goto unlock;
+	}
+
 	ret = cache_kset_insert_tree(cache, kset_onmedia);
 	if (ret) {
 		delay = PCACHE_CACHE_WRITEBACK_INTERVAL;
-- 
2.53.0