net: unix: allow set_peek_off to fail

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@oracle.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 8 insertions, 4 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index 4bcee94cef93..69be3e6079c8 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -181,7 +181,7 @@ 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 ab20ed9b0f31..5393b4b719d7 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -882,7 +882,7 @@ 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 01625ccc3ae6..a0ca162e5bd5 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;
 }