[PATCH v2 2/2] smb: client: clear ce->tgthint in free_tgts()

[Fredric Cover]

When free_tgts() frees all structures in ce->tlist, ce->tgthint
is left pointing to one of the freed cache_dfs_tgt structures.

If ce->tgthint is not reset before it is used later, it results
in a use-after-free.

Set ce->tgthint to NULL in free_tgts() after the elements are
freed to reflect that no elements remain.

Fixes: 54be1f6c1c37 ("cifs: Add DFS cache routines")
Cc: stable@xxxxxxxxxxxxxxx # depends on: smb: client: harden DFS cache against invalid target hints
Signed-off-by: Fredric Cover <fredric.cover.lkernel@xxxxxxxxx>
---
 fs/smb/client/dfs_cache.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/smb/client/dfs_cache.c b/fs/smb/client/dfs_cache.c
index c9ace4326a35..86dba25b7a5a 100644
--- a/fs/smb/client/dfs_cache.c
+++ b/fs/smb/client/dfs_cache.c
@@ -122,6 +122,8 @@ static inline void free_tgts(struct cache_entry *ce)
 		kfree(t->name);
 		kfree(t);
 	}
+
+	WRITE_ONCE(ce->tgthint, NULL);
 }
 
 static inline void flush_cache_ent(struct cache_entry *ce)
-- 
2.53.0