netdev - [PATCH v2] ipsec: Fix aborted xfrm policy dump crash

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Date:   Thu, 19 Oct 2017 20:51:10 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Timo Teras <timo.teras@....fi>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        netdev@...r.kernel.org
Subject: [PATCH v2] ipsec: Fix aborted xfrm policy dump crash

On Thu, Oct 19, 2017 at 02:33:20PM +0300, Timo Teras wrote:
>
> > Fixes: 4c563f7669c1 ("[XFRM]: Speed up xfrm_policy and xfrm_state...")
> 
> This is not correct. The original commit works just fine.

OK, I'll change it.

> At that time there was no .start which got added just few years ago. I
> suggest to do the same fix for SA side since it had same issue fixed on
> the other commit. Your approach with defining the .start is cleaner.

No we can't use the start on the SA side because as it is start
is not allowed to fail.

Thanks,

---8<---
An independent security researcher, Mohamed Ghannam, has reported
this vulnerability to Beyond Security's SecuriTeam Secure Disclosure
program.

The xfrm_dump_policy_done function expects xfrm_dump_policy to
have been called at least once or it will crash.  This can be
triggered if a dump fails because the target socket's receive
buffer is full.

This patch fixes it by using the cb->start mechanism to ensure that
the initialisation is always done regardless of the buffer situation.

Fixes: 12a169e7d8f4 ("ipsec: Put dumpers on the dump list")
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 2bfbd91..98a6d65 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1692,32 +1692,34 @@ static int dump_one_policy(struct xfrm_policy *xp, int dir, int count, void *ptr
 
 static int xfrm_dump_policy_done(struct netlink_callback *cb)
 {
-	struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *) &cb->args[1];
+	struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *)cb->args;
 	struct net *net = sock_net(cb->skb->sk);
 
 	xfrm_policy_walk_done(walk, net);
 	return 0;
 }
 
+static int xfrm_dump_policy_start(struct netlink_callback *cb)
+{
+	struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *)cb->args;
+
+	BUILD_BUG_ON(sizeof(*walk) > sizeof(cb->args));
+
+	xfrm_policy_walk_init(walk, XFRM_POLICY_TYPE_ANY);
+	return 0;
+}
+
 static int xfrm_dump_policy(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct net *net = sock_net(skb->sk);
-	struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *) &cb->args[1];
+	struct xfrm_policy_walk *walk = (struct xfrm_policy_walk *)cb->args;
 	struct xfrm_dump_info info;
 
-	BUILD_BUG_ON(sizeof(struct xfrm_policy_walk) >
-		     sizeof(cb->args) - sizeof(cb->args[0]));
-
 	info.in_skb = cb->skb;
 	info.out_skb = skb;
 	info.nlmsg_seq = cb->nlh->nlmsg_seq;
 	info.nlmsg_flags = NLM_F_MULTI;
 
-	if (!cb->args[0]) {
-		cb->args[0] = 1;
-		xfrm_policy_walk_init(walk, XFRM_POLICY_TYPE_ANY);
-	}
-
 	(void) xfrm_policy_walk(net, walk, dump_one_policy, &info);
 
 	return skb->len;
@@ -2473,6 +2475,7 @@ static int xfrm_send_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
 
 static const struct xfrm_link {
 	int (*doit)(struct sk_buff *, struct nlmsghdr *, struct nlattr **);
+	int (*start)(struct netlink_callback *);
 	int (*dump)(struct sk_buff *, struct netlink_callback *);
 	int (*done)(struct netlink_callback *);
 	const struct nla_policy *nla_pol;
@@ -2486,6 +2489,7 @@ static int xfrm_send_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
 	[XFRM_MSG_NEWPOLICY   - XFRM_MSG_BASE] = { .doit = xfrm_add_policy    },
 	[XFRM_MSG_DELPOLICY   - XFRM_MSG_BASE] = { .doit = xfrm_get_policy    },
 	[XFRM_MSG_GETPOLICY   - XFRM_MSG_BASE] = { .doit = xfrm_get_policy,
+						   .start = xfrm_dump_policy_start,
 						   .dump = xfrm_dump_policy,
 						   .done = xfrm_dump_policy_done },
 	[XFRM_MSG_ALLOCSPI    - XFRM_MSG_BASE] = { .doit = xfrm_alloc_userspi },
@@ -2538,6 +2542,7 @@ static int xfrm_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 		{
 			struct netlink_dump_control c = {
+				.start = link->start,
 				.dump = link->dump,
 				.done = link->done,
 			};

-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt