[PATCH v3 1/3] unix/dgram: peek beyond 0-sized skbs

From: Benjamin Poirier
Date: Mon Apr 29 2013 - 17:42:47 EST

"77c1090 net: fix infinite loop in __skb_recv_datagram()" (v3.8) introduced a
After that commit, recv can no longer peek beyond a 0-sized skb in the queue.
__skb_recv_datagram() instead stops at the first skb with len == 0 and results
in the system call failing with -EFAULT via skb_copy_datagram_iovec().

When peeking at an offset with 0-sized skb(s), each one of those is received
only once, in sequence. The offset starts moving forward again after receiving
datagrams with len > 0.

Signed-off-by: Benjamin Poirier <bpoirier@xxxxxxx>


* v1 fix the case when SO_PEEK_OFF is used to set sk_peek_off beyond a
0-sized skb

* v2 also fix the situation when sk_peek_off must advance to and beyond a
0-sized skb

net/core/datagram.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 368f9c3..99c4f52 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -187,7 +187,8 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
skb_queue_walk(queue, skb) {
*peeked = skb->peeked;
if (flags & MSG_PEEK) {
- if (*off >= skb->len && skb->len) {
+ if (*off >= skb->len && (skb->len || *off ||
+ skb->peeked)) {
*off -= skb->len;

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