[3.11.y.z extended stable] Patch "net: unix: allow set_peek_off to fail" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    net: unix: allow set_peek_off to fail

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 6e5ef2a7442c9eb478e21a4919a3cc1af7843008 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sasha.levin at oracle.com>
Date: Sat, 7 Dec 2013 17:26:27 -0500
Subject: net: unix: allow set_peek_off to fail

commit 12663bfc97c8b3fdb292428105dd92d563164050 upstream.

unix_dgram_recvmsg() will hold the readlock of the socket until recv
is complete.

In the same time, we may try to setsockopt(SO_PEEK_OFF) which will hang until
unix_dgram_recvmsg() will complete (which can take a while) without allowing
us to break out of it, triggering a hung task spew.

Instead, allow set_peek_off to fail, this way userspace will not hang.

Signed-off-by: Sasha Levin <sasha.levin at oracle.com>
Acked-by: Pavel Emelyanov <xemul at parallels.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 include/linux/net.h | 2 +-
 net/core/sock.c     | 2 +-
 net/unix/af_unix.c  | 8 ++++++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/net.h b/include/linux/net.h
index 8bd9d92..41103f8 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -180,7 +180,7 @@ struct proto_ops {
 				      int offset, size_t size, int flags);
 	ssize_t 	(*splice_read)(struct socket *sock,  loff_t *ppos,
 				       struct pipe_inode_info *pipe, size_t len, unsigned int flags);
-	void		(*set_peek_off)(struct sock *sk, int val);
+	int		(*set_peek_off)(struct sock *sk, int val);
 };

 #define DECLARE_SOCKADDR(type, dst, src)	\
diff --git a/net/core/sock.c b/net/core/sock.c
index 8729d91..dca3102 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -887,7 +887,7 @@ set_rcvbuf:

 	case SO_PEEK_OFF:
 		if (sock->ops->set_peek_off)
-			sock->ops->set_peek_off(sk, val);
+			ret = sock->ops->set_peek_off(sk, val);
 		else
 			ret = -EOPNOTSUPP;
 		break;
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 6c66e8d..303dcec 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -530,13 +530,17 @@ static int unix_seqpacket_sendmsg(struct kiocb *, struct socket *,
 static int unix_seqpacket_recvmsg(struct kiocb *, struct socket *,
 				  struct msghdr *, size_t, int);

-static void unix_set_peek_off(struct sock *sk, int val)
+static int unix_set_peek_off(struct sock *sk, int val)
 {
 	struct unix_sock *u = unix_sk(sk);

-	mutex_lock(&u->readlock);
+	if (mutex_lock_interruptible(&u->readlock))
+		return -EINTR;
+
 	sk->sk_peek_off = val;
 	mutex_unlock(&u->readlock);
+
+	return 0;
 }


--
1.8.3.2