[PATCH bpf-next 2/2] bpf, sockmap: Use sock_hold() instead of refcount_inc_not_zero() in lookup

[Michal Luczaj <mhal@rbox.co>]

psock's hold on the looked up socket isn't dropped until sk_psock_drop() ->
queue_rcu_work() -> sk_psock_destroy() runs, which happens only after the
entry is unlinked and an RCU grace period elapses. Since the lookup runs
under RCU, a non-NULL result guarantees sk_refcnt >= 1:
refcount_inc_not_zero() can never fail here. Use sock_hold() instead.

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
---
 net/core/sock_map.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 9efbd8ca7db8..ca49bc7f8687 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -392,8 +392,8 @@ static void *sock_map_lookup(struct bpf_map *map, void *key)
 	sk = __sock_map_lookup_elem(map, *(u32 *)key);
 	if (!sk)
 		return NULL;
-	if (sk_is_refcounted(sk) && !refcount_inc_not_zero(&sk->sk_refcnt))
-		return NULL;
+	if (sk_is_refcounted(sk))
+		sock_hold(sk);
 	return sk;
 }
 
@@ -1218,8 +1218,8 @@ static void *sock_hash_lookup(struct bpf_map *map, void *key)
 	sk = __sock_hash_lookup_elem(map, key);
 	if (!sk)
 		return NULL;
-	if (sk_is_refcounted(sk) && !refcount_inc_not_zero(&sk->sk_refcnt))
-		return NULL;
+	if (sk_is_refcounted(sk))
+		sock_hold(sk);
 	return sk;
 }
 

-- 
2.55.0