netdev - [PATCH net 1/1] tipc: move premature initilalization of stack variables

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Message-Id: <1487866231-23666-1-git-send-email-jon.maloy@ericsson.com>
Date:   Thu, 23 Feb 2017 11:10:31 -0500
From:   Jon Maloy <jon.maloy@...csson.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, parthasarathy.bhuvaragan@...csson.com,
        ying.xue@...driver.com, maloy@...jonn.com,
        tipc-discussion@...ts.sourceforge.net,
        Jon Maloy <jon.maloy@...csson.com>
Subject: [PATCH net 1/1] tipc: move premature initilalization of stack variables

In the function tipc_rcv() we initialize a couple of stack variables
from the message header before that same header has been validated.
In rare cases when the arriving header is non-linar, the validation
function itself may linearize the buffer by calling skb_may_pull(),
while the wrongly initialized stack fields are not updated accordingly.

We fix this in this commit.

Reported-by: Matthew Wong <mwong@...usnet.com>
Signed-off-by: Jon Maloy <jon.maloy@...csson.com>
---
 net/tipc/node.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index e9295fa..4512e83 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -1505,19 +1505,21 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 {
 	struct sk_buff_head xmitq;
 	struct tipc_node *n;
-	struct tipc_msg *hdr = buf_msg(skb);
-	int usr = msg_user(hdr);
+	struct tipc_msg *hdr;
 	int bearer_id = b->identity;
 	struct tipc_link_entry *le;
-	u16 bc_ack = msg_bcast_ack(hdr);
 	u32 self = tipc_own_addr(net);
-	int rc = 0;
+	int usr, rc = 0;
+	u16 bc_ack;
 
 	__skb_queue_head_init(&xmitq);
 
-	/* Ensure message is well-formed */
+	/* Ensure message is well-formed before touching the header */
 	if (unlikely(!tipc_msg_validate(skb)))
 		goto discard;
+	hdr = buf_msg(skb);
+	usr = msg_user(hdr);
+	bc_ack = msg_bcast_ack(hdr);
 
 	/* Handle arrival of discovery or broadcast packet */
 	if (unlikely(msg_non_seq(hdr))) {
-- 
2.7.4