socket: skip checking sk_err for recvmmsg(MSG_ERRQUEUE)

recvmmsg does not call ___sys_recvmsg when sk_err is set.
That is fine for normal reads but, for MSG_ERRQUEUE, recvmmsg
should always call ___sys_recvmsg regardless of sk->sk_err to
be able to clear error queue. Otherwise, users are not able to
drain the error queue using recvmmsg.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/socket.c b/net/socket.c
index 645d32b..d9a1ac2 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -2289,10 +2289,12 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
        if (!sock)
                return err;
 
-       err = sock_error(sock->sk);
-       if (err) {
-               datagrams = err;
-               goto out_put;
+       if (likely(!(flags & MSG_ERRQUEUE))) {
+               err = sock_error(sock->sk);
+               if (err) {
+                       datagrams = err;
+                       goto out_put;
+               }
        }
 
        entry = mmsg;