net: unix: non blocking recvmsg() should not return -EINTR

[ Upstream commit de1443916791d75fdd26becb116898277bb0273f ]

Some applications didn't expect recvmsg() on a non blocking socket
could return -EINTR. This possibility was added as a side effect
of commit b3ca9b02b00704 ("net: fix multithreaded signal handling in
unix recv routines").

To hit this bug, you need to be a bit unlucky, as the u->readlock
mutex is usually held for very small periods.

Fixes: b3ca9b02b00704 ("net: fix multithreaded signal handling in unix recv routines")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 54fc90b..8705ee3 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1771,8 +1771,11 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
                goto out;
 
        err = mutex_lock_interruptible(&u->readlock);
-       if (err) {
-               err = sock_intr_errno(sock_rcvtimeo(sk, noblock));
+       if (unlikely(err)) {
+               /* recvmsg() in non blocking mode is supposed to return -EAGAIN
+                * sk_rcvtimeo is not honored by mutex_lock_interruptible()
+                */
+               err = noblock ? -EAGAIN : -ERESTARTSYS;
                goto out;
        }
 
@@ -1887,6 +1890,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
        struct unix_sock *u = unix_sk(sk);
        struct sockaddr_un *sunaddr = msg->msg_name;
        int copied = 0;
+       int noblock = flags & MSG_DONTWAIT;
        int check_creds = 0;
        int target;
        int err = 0;
@@ -1901,7 +1905,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
                goto out;
 
        target = sock_rcvlowat(sk, flags&MSG_WAITALL, size);
-       timeo = sock_rcvtimeo(sk, flags&MSG_DONTWAIT);
+       timeo = sock_rcvtimeo(sk, noblock);
 
        /* Lock the socket to prevent queue disordering
         * while sleeps in memcpy_tomsg
@@ -1913,8 +1917,11 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
        }
 
        err = mutex_lock_interruptible(&u->readlock);
-       if (err) {
-               err = sock_intr_errno(timeo);
+       if (unlikely(err)) {
+               /* recvmsg() in non blocking mode is supposed to return -EAGAIN
+                * sk_rcvtimeo is not honored by mutex_lock_interruptible()
+                */
+               err = noblock ? -EAGAIN : -ERESTARTSYS;
                goto out;
        }