[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@xxxxxxxxxx>

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@xxxxxxxxxxxxx> (maintainer:NETWORKING
Cc: Eric Dumazet <edumazet@xxxxxxxxxx> (commit_signer:1/14=7%)
Cc: Aaron Conole <aconole@xxxxxxxxxx>
Fixes: 9f389e35674f ("af_unix: return data from multiple SKBs on recv() with MSG_PEEK flag")
Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
Tested-by: Aaron Conole <aconole@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 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);
--
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