xsk: do not call synchronize_net() under RCU read lock

[ Upstream commit cee271678d0e3177a25d0fcb2fa5e051d48e4262 ]

The XSKMAP update and delete functions called synchronize_net(), which
can sleep. It is not allowed to sleep during an RCU read section.

Instead we need to make sure that the sock sk_destruct (xsk_destruct)
function is asynchronously called after an RCU grace period. Setting
the SOCK_RCU_FREE flag for XDP sockets takes care of this.

Fixes: fbfc504a24f5 ("bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE_XSKMAP")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
index b3c557476a8d933730d48b373e80c4b3daf8eb8c..c98501a0474271e168a7cdd915af856f5f7ce706 100644 (file)
--- a/kernel/bpf/xskmap.c
+++ b/kernel/bpf/xskmap.c
@@ -191,11 +191,8 @@ static int xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
        sock_hold(sock->sk);
 
        old_xs = xchg(&m->xsk_map[i], xs);
-       if (old_xs) {
-               /* Make sure we've flushed everything. */
-               synchronize_net();
+       if (old_xs)
                sock_put((struct sock *)old_xs);
-       }
 
        sockfd_put(sock);
        return 0;
@@ -211,11 +208,8 @@ static int xsk_map_delete_elem(struct bpf_map *map, void *key)
                return -EINVAL;
 
        old_xs = xchg(&m->xsk_map[k], NULL);
-       if (old_xs) {
-               /* Make sure we've flushed everything. */
-               synchronize_net();
+       if (old_xs)
                sock_put((struct sock *)old_xs);
-       }
 
        return 0;
 }

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 4e937cd7c17dc6b4b617f463336e9a8d2867ed6d..661504042d3040dd01cf3ef56955d6f93b467e76 100644 (file)
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -744,6 +744,8 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
        sk->sk_destruct = xsk_destruct;
        sk_refcnt_debug_inc(sk);
 
+       sock_set_flag(sk, SOCK_RCU_FREE);
+
        xs = xdp_sk(sk);
        mutex_init(&xs->mutex);
        spin_lock_init(&xs->tx_completion_lock);