[PATCH 6.4 663/800] net/sched: act_ipt: add sanity checks on skb before calling target

Greg Kroah-Hartman
2023-07-16T20:25:14Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit b2dc32dcba08bf55cec600caa76f4afd2e3614df ]

Netfilter targets make assumptions on the skb state, for example
iphdr is supposed to be in the linear area.

This is normally done by IP stack, but in act_ipt case no
such checks are made.

Some targets can even assume that skb_dst will be valid.
Make a minimum effort to check for this:

- Don't call the targets eval function for non-ipv4 skbs.
- Don't call the targets eval function for POSTROUTING
emulation when the skb has no dst set.

v3: use skb_protocol helper (Davide Caratti)

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/act_ipt.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
index ea7f151e7dd29..a6b522b512dc3 100644
--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c
@@ -230,6 +230,26 @@ static int tcf_xt_init(struct net *net, struct nlattr *nla,
a, &act_xt_ops, tp, flags);
}

+static bool tcf_ipt_act_check(struct sk_buff *skb)
+{
+ const struct iphdr *iph;
+ unsigned int nhoff, len;
+
+ if (!pskb_may_pull(skb, sizeof(struct iphdr)))
+ return false;
+
+ nhoff = skb_network_offset(skb);
+ iph = ip_hdr(skb);
+ if (iph->ihl < 5 || iph->version != 4)
+ return false;
+
+ len = skb_ip_totlen(skb);
+ if (skb->len < nhoff + len || len < (iph->ihl * 4u))
+ return false;
+
+ return pskb_may_pull(skb, iph->ihl * 4u);
+}
+
TC_INDIRECT_SCOPE int tcf_ipt_act(struct sk_buff *skb,
const struct tc_action *a,
struct tcf_result *res)
@@ -244,9 +264,22 @@ TC_INDIRECT_SCOPE int tcf_ipt_act(struct sk_buff *skb,
.pf = NFPROTO_IPV4,
};

+ if (skb_protocol(skb, false) != htons(ETH_P_IP))
+ return TC_ACT_UNSPEC;
+
if (skb_unclone(skb, GFP_ATOMIC))
return TC_ACT_UNSPEC;

+ if (!tcf_ipt_act_check(skb))
+ return TC_ACT_UNSPEC;
+
+ if (state.hook == NF_INET_POST_ROUTING) {
+ if (!skb_dst(skb))
+ return TC_ACT_UNSPEC;
+
+ state.out = skb->dev;
+ }
+
spin_lock(&ipt->tcf_lock);

tcf_lastuse_update(&ipt->tcf_tm);
--
2.39.2