sock_map: fix a NULL pointer dereference in sock_map_link_update_prog()

The following race condition could trigger a NULL pointer dereference:

sock_map_link_detach():		sock_map_link_update_prog():
   mutex_lock(&sockmap_mutex);
   ...
   sockmap_link->map = NULL;
   mutex_unlock(&sockmap_mutex);
   				   mutex_lock(&sockmap_mutex);
				   ...
				   sock_map_prog_link_lookup(sockmap_link->map);
				   mutex_unlock(&sockmap_mutex);
   <continue>

Fix it by adding a NULL pointer check. In this specific case, it makes
no sense to update a link which is being released.

Reported-by: Ruan Bonan <bonan.ruan@u.nus.edu>
Fixes: 699c23f02c65 ("bpf: Add bpf_link support for sk_msg and sk_skb progs")
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Link: https://lore.kernel.org/r/20241026185522.338562-1-xiyou.wangcong@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 07d6aa4e39ef606aab33bd0d95711ecf156596b9..78347d7d25ef31525f8ec0a755a18e5793ad92c0 100644 (file)
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -1760,6 +1760,10 @@ static int sock_map_link_update_prog(struct bpf_link *link,
                ret = -EINVAL;
                goto out;
        }
+       if (!sockmap_link->map) {
+               ret = -ENOLINK;
+               goto out;
+       }
 
        ret = sock_map_prog_link_lookup(sockmap_link->map, &pprog, &plink,
                                        sockmap_link->attach_type);