[PATCH 3.16.y-ckt 096/104] net/unix: fix logic about sk_peek_offset

[Luis Henriques]

3.16.7-ckt19 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Vagin <avagin at openvz.org>

commit e9193d60d363e4dff75ff6d43a48f22be26d59c7 upstream.

Now send with MSG_PEEK can return data from multiple SKBs.

Unfortunately we take into account the peek offset for each skb,
that is wrong. We need to apply the peek offset only once.

In addition, the peek offset should be used only if MSG_PEEK is set.

Cc: "David S. Miller" <davem at davemloft.net> (maintainer:NETWORKING
Cc: Eric Dumazet <edumazet at google.com> (commit_signer:1/14=7%)
Cc: Aaron Conole <aconole at bytheb.org>
Fixes: 9f389e35674f ("af_unix: return data from multiple SKBs on recv() with MSG_PEEK flag")
Signed-off-by: Andrey Vagin <avagin at openvz.org>
Tested-by: Aaron Conole <aconole at bytheb.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/unix/af_unix.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 30a705ee0ac8..2ae4a5915aa7 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1962,6 +1962,11 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
 		goto out;
 	}
 
+	if (flags & MSG_PEEK)
+		skip = sk_peek_offset(sk, flags);
+	else
+		skip = 0;
+
 	do {
 		int chunk;
 		struct sk_buff *skb, *last;
@@ -2008,7 +2013,6 @@ again:
 			break;
 		}
 
-		skip = sk_peek_offset(sk, flags);
 		while (skip >= unix_skb_len(skb)) {
 			skip -= unix_skb_len(skb);
 			last = skb;
@@ -2070,14 +2074,12 @@ again:
 			if (UNIXCB(skb).fp)
 				siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
 
-			if (skip) {
-				sk_peek_offset_fwd(sk, chunk);
-				skip -= chunk;
-			}
+			sk_peek_offset_fwd(sk, chunk);
 
 			if (UNIXCB(skb).fp)
 				break;
 
+			skip = 0;
 			last = skb;
 			unix_state_lock(sk);
 			skb = skb_peek_next(skb, &sk->sk_receive_queue);