[PATCH 3.16 080/346] xfrm: fix crash in XFRM_MSG_GETSA netlink handler

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Vegard Nossum <vegard.nossum@xxxxxxxxxx>

commit 1ba5bf993c6a3142e18e68ea6452b347f9cb5635 upstream.

If we hit any of the error conditions inside xfrm_dump_sa(), then
xfrm_state_walk_init() never gets called. However, we still call
xfrm_state_walk_done() from xfrm_dump_sa_done(), which will crash
because the state walk was never initialized properly.

We can fix this by setting cb->args[0] only after we've processed the
first element and checking this before calling xfrm_state_walk_done().

Fixes: d3623099d3 ("ipsec: add support of limited SA dump")
Cc: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Acked-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/xfrm/xfrm_user.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -869,7 +869,8 @@ static int xfrm_dump_sa_done(struct netl
 	struct sock *sk = cb->skb->sk;
 	struct net *net = sock_net(sk);
 
-	xfrm_state_walk_done(walk, net);
+	if (cb->args[0])
+		xfrm_state_walk_done(walk, net);
 	return 0;
 }
 
@@ -894,8 +895,6 @@ static int xfrm_dump_sa(struct sk_buff *
 		u8 proto = 0;
 		int err;
 
-		cb->args[0] = 1;
-
 		err = nlmsg_parse(cb->nlh, 0, attrs, XFRMA_MAX,
 				  xfrma_policy);
 		if (err < 0)
@@ -914,6 +913,7 @@ static int xfrm_dump_sa(struct sk_buff *
 			proto = nla_get_u8(attrs[XFRMA_PROTO]);
 
 		xfrm_state_walk_init(walk, proto, filter);
+		cb->args[0] = 1;
 	}
 
 	(void) xfrm_state_walk(net, walk, dump_one_state, &info);