net/packet: annotate data race in packet_sendmsg()

There is a known race in packet_sendmsg(), addressed
in commit 32d3182cd2cd ("net/packet: fix race in tpacket_snd()")

Now we have data_race(), we can use it to avoid a future KCSAN warning,
as syzbot loves stressing af_packet sockets :)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ae906eb..74e6e45 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3034,10 +3034,13 @@ static int packet_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
        struct sock *sk = sock->sk;
        struct packet_sock *po = pkt_sk(sk);
 
-       if (po->tx_ring.pg_vec)
+       /* Reading tx_ring.pg_vec without holding pg_vec_lock is racy.
+        * tpacket_snd() will redo the check safely.
+        */
+       if (data_race(po->tx_ring.pg_vec))
                return tpacket_snd(po, msg);
-       else
-               return packet_snd(sock, msg, len);
+
+       return packet_snd(sock, msg, len);
 }
 
 /*