[PATCH net 2/3] unix/dgram: fix peeking with an offset larger than data in queue

Benjamin Poirier
2013-04-25T13:47:17Z

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>
---
net/core/datagram.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 02398ae..6c502b5 100644
--- 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,
+ 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 ((struct sk_buff *)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
- * @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
+ * @_off: an offset in bytes to peek skb from. Returns an offset
+ * within an skb where data actually starts
* @err: error code returned
*
* Get a datagram skbuff, understands the peeking, nonblocking wakeups
@@ -159,9 +160,9 @@ out_noerr:
* the standard around please.
*/
struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
- int *peeked, int *off, int *err)
+ 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()
@@ -182,13 +183,16 @@ 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;

spin_lock_irqsave(&queue->lock, cpu_flags);
+ last = (struct sk_buff *)queue;
skb_queue_walk(queue, skb) {
+ last = skb;
*peeked = skb->peeked;
if (flags & MSG_PEEK) {
- if (*off >= skb->len && (skb->len || *off)) {
- *off -= skb->len;
+ if (off >= skb->len && (skb->len || off)) {
+ off -= skb->len;
continue;
}
skb->peeked = 1;
@@ -197,6 +201,7 @@ 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);
@@ -206,7 +211,7 @@ 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;

--
1.7.10.4