ipsec: Fix aborted xfrm policy dump crash

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@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index b997f1395357e8696657d3c07b04318b908fff89..e44a0fed48dd088ac95a0726a5f2b58b0f07c5bb 100644 (file)
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1693,32 +1693,34 @@ 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;
@@ -2474,6 +2476,7 @@ static const struct nla_policy xfrma_spd_policy[XFRMA_SPD_MAX+1] = {
 
 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;
@@ -2487,6 +2490,7 @@ static const struct xfrm_link {
        [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 },
@@ -2539,6 +2543,7 @@ 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,
                        };