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

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>

1 files changed, 12 insertions, 5 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ce6ec6c2f4de..94404f19f9de 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1787,8 +1787,11 @@ 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;
         }
 
@@ -1913,6 +1916,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
         struct unix_sock *u = unix_sk(sk);
         DECLARE_SOCKADDR(struct sockaddr_un *, sunaddr, msg->msg_name);
         int copied = 0;
+        int noblock = flags & MSG_DONTWAIT;
         int check_creds = 0;
         int target;
         int err = 0;
@@ -1928,7 +1932,7 @@ 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
@@ -1940,8 +1944,11 @@ 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;
         }