[PATCH net-next] net: fix __skb_try_recv_from_queue to return the old behavior

[Andrei Vagin]

This function has to return NULL on a error case, because there is a
separate error variable.

The offset has to be changed only if skb is returned

Cc: Paolo Abeni <pab...@redhat.com>
Cc: Eric Dumazet <eduma...@google.com>
Cc: David S. Miller <da...@davemloft.net>
Fixes: 65101aeca522 ("net/sock: factor out dequeue/peek with offset cod")
Signed-off-by: Andrei Vagin <ava...@openvz.org>
---
 net/core/datagram.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index a4592b4..bc46118 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -170,20 +170,21 @@ struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
                                          struct sk_buff **last)
 {
        struct sk_buff *skb;
+       int _off = *off;
 
        *last = queue->prev;
        skb_queue_walk(queue, skb) {
                if (flags & MSG_PEEK) {
-                       if (*off >= skb->len && (skb->len || *off ||
+                       if (_off >= skb->len && (skb->len || _off ||
                                                 skb->peeked)) {
-                               *off -= skb->len;
+                               _off -= skb->len;
                                continue;
                        }
                        if (!skb->len) {
                                skb = skb_set_peeked(skb);
                                if (unlikely(IS_ERR(skb))) {
                                        *err = PTR_ERR(skb);
-                                       return skb;
+                                       return NULL;
                                }
                        }
                        *peeked = 1;
@@ -193,6 +194,7 @@ struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
                        if (destructor)
                                destructor(sk, skb);
                }
+               *off = _off;
                return skb;
        }
        return NULL;
@@ -253,8 +255,6 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, 
unsigned int flags,
 
        *peeked = 0;
        do {
-               int _off = *off;
-
                /* Again only user level code calls this function, so nothing
                 * interrupt level will suddenly eat the receive_queue.
                 *
@@ -263,8 +263,10 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, 
unsigned int flags,
                 */
                spin_lock_irqsave(&queue->lock, cpu_flags);
                skb = __skb_try_recv_from_queue(sk, queue, flags, destructor,
-                                               peeked, &_off, err, last);
+                                               peeked, off, &error, last);
                spin_unlock_irqrestore(&queue->lock, cpu_flags);
+               if (error)
+                       goto no_packet;
                if (skb)
                        return skb;
 
-- 
2.9.3