Patch "net/sched: act_ipt: add sanity checks on skb before calling target" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net/sched: act_ipt: add sanity checks on skb before calling target

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-sched-act_ipt-add-sanity-checks-on-skb-before-ca.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 729bf094b7aa56b2f2fbf39514d0999b1af165eb
Author: Florian Westphal <fw@xxxxxxxxx>
Date:   Tue Jun 27 14:38:12 2023 +0200

    net/sched: act_ipt: add sanity checks on skb before calling target
    
    [ 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@xxxxxxxxx>
    Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
    Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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);