unix/dgram: fix peeking with an offset larger than data in queue

Currently, peeking on a unix datagram socket with an offset larger than len of
the data in the sk receive queue returns immediately with bogus data. That's
because *off is not reset between each skb_queue_walk().

This patch fixes this so that the behavior is the same as peeking with no
offset on an empty queue: the caller blocks.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 99c4f52..b5d48ac 100644 (file)
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -78,9 +78,10 @@ static int receiver_wake_function(wait_queue_t *wait, unsigned int mode, int syn
        return autoremove_wake_function(wait, mode, sync, key);
 }
 /*
- * Wait for a packet..
+ * Wait for the last received packet to be different from skb
  */
-static int wait_for_packet(struct sock *sk, int *err, long *timeo_p)
+static int wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
+                                const struct sk_buff *skb)
 {
        int error;
        DEFINE_WAIT_FUNC(wait, receiver_wake_function);
@@ -92,7 +93,7 @@ static int wait_for_packet(struct sock *sk, int *err, long *timeo_p)
        if (error)
                goto out_err;
 
-       if (!skb_queue_empty(&sk->sk_receive_queue))
+       if (sk->sk_receive_queue.prev != skb)
                goto out;
 
        /* Socket shut down? */
@@ -131,9 +132,9 @@ out_noerr:
  *     __skb_recv_datagram - Receive a datagram skbuff
  *     @sk: socket
  *     @flags: MSG_ flags
+ *     @peeked: returns non-zero if this packet has been seen before
  *     @off: an offset in bytes to peek skb from. Returns an offset
  *           within an skb where data actually starts
- *     @peeked: returns non-zero if this packet has been seen before
  *     @err: error code returned
  *
  *     Get a datagram skbuff, understands the peeking, nonblocking wakeups
@@ -161,7 +162,7 @@ out_noerr:
 struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
                                    int *peeked, int *off, int *err)
 {
-       struct sk_buff *skb;
+       struct sk_buff *skb, *last;
        long timeo;
        /*
         * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
@@ -182,14 +183,17 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
                 */
                unsigned long cpu_flags;
                struct sk_buff_head *queue = &sk->sk_receive_queue;
+               int _off = *off;
 
+               last = (struct sk_buff *)queue;
                spin_lock_irqsave(&queue->lock, cpu_flags);
                skb_queue_walk(queue, skb) {
+                       last = skb;
                        *peeked = skb->peeked;
                        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;
                                }
                                skb->peeked = 1;
@@ -198,6 +202,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
                                __skb_unlink(skb, queue);
 
                        spin_unlock_irqrestore(&queue->lock, cpu_flags);
+                       *off = _off;
                        return skb;
                }
                spin_unlock_irqrestore(&queue->lock, cpu_flags);
@@ -207,7 +212,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
                if (!timeo)
                        goto no_packet;
 
-       } while (!wait_for_packet(sk, err, &timeo));
+       } while (!wait_for_more_packets(sk, err, &timeo, last));
 
        return NULL;