[PATCH 3.8 003/133] net: unix: non blocking recvmsg() should not return -EINTR

From: Kamal Mostafa
Date: Tue Apr 22 2014 - 17:40:20 EST


3.8.13.22 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[ kamal removed Cc: Rainer Weikusat per request ]
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
net/unix/af_unix.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 72f4e97..3887f23 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1795,8 +1795,11 @@ 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;
}

@@ -1918,6 +1921,7 @@ 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;
@@ -1933,7 +1937,7 @@ 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
@@ -1945,8 +1949,11 @@ 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;
}

--
1.9.1

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