[3.19.y-ckt stable] Patch "tipc: allow non-linear first fragment buffer" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    tipc: allow non-linear first fragment buffer

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From f05773e636ededcdcc3c973d593be9e3b1d2215c Mon Sep 17 00:00:00 2001
From: Jon Paul Maloy <jon.maloy at ericsson.com>
Date: Mon, 19 Oct 2015 11:33:00 -0400
Subject: tipc: allow non-linear first fragment buffer

[ Upstream commit 45c8b7b175ceb2d542e0fe15247377bf3bce29ec ]

The current code for message reassembly is erroneously assuming that
the the first arriving fragment buffer always is linear, and then goes
ahead resetting the fragment list of that buffer in anticipation of
more arriving fragments.

However, if the buffer already happens to be non-linear, we will
inadvertently drop the already attached fragment list, and later
on trig a BUG() in __pskb_pull_tail().

We see this happen when running fragmented TIPC multicast across UDP,
something made possible since
commit d0f91938bede ("tipc: add ip/udp media type")

We fix this by not resetting the fragment list when the buffer is non-
linear, and by initiatlizing our private fragment list tail pointer to
the tail of the existing fragment list.

Fixes: commit d0f91938bede ("tipc: add ip/udp media type")
Signed-off-by: Jon Maloy <jon.maloy at ericsson.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/tipc/msg.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index a687b30..2baa992 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -98,7 +98,7 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf)
 {
 	struct sk_buff *head = *headbuf;
 	struct sk_buff *frag = *buf;
-	struct sk_buff *tail;
+	struct sk_buff *tail = NULL;
 	struct tipc_msg *msg;
 	u32 fragid;
 	int delta;
@@ -118,9 +118,15 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf)
 		if (unlikely(skb_unclone(frag, GFP_ATOMIC)))
 			goto err;
 		head = *headbuf = frag;
-		skb_frag_list_init(head);
-		TIPC_SKB_CB(head)->tail = NULL;
 		*buf = NULL;
+		TIPC_SKB_CB(head)->tail = NULL;
+		if (skb_is_nonlinear(head)) {
+			skb_walk_frags(head, tail) {
+				TIPC_SKB_CB(head)->tail = tail;
+			}
+		} else {
+			skb_frag_list_init(head);
+		}
 		return 0;
 	}

--
1.9.1