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@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 08b4cc7d496d94c80fb2fcacc30ade0192fb0dc8..b3a393104b17dcda19e85a3ba022d2ea529a4030 100644 (file)
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -121,7 +121,7 @@ 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;
@@ -141,9 +141,15 @@ 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;
        }