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netfilter: nf_reject: initialize IPCB at inet ingress

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The inet ingress hook runs before ip_rcv_core() and ip6_rcv_core(), so
neither IPCB nor IP6CB has been initialized when nft_reject_inet passes
a packet to nf_send_unreach() or nf_send_unreach6(). skb->cb can
therefore retain metadata from an earlier protocol layer.

For IPv4, icmp_send() treats IPCB(skb)->opt as parsed IPv4 options.
Stale option offsets can make __ip_options_echo() copy an
attacker-controlled length into its 40-byte reply option buffer and
overflow the stack. On an unpatched v7.2-rc5 kernel, the IPv4
reproducer produced:

  BUG: KASAN: stack-out-of-bounds in __ip_options_echo()
  Write of size 255

For IPv6, icmpv6_send() consumes IP6CB(skb) as parsed IPv6 metadata. It
always uses iif for source selection and, when MIP6 is enabled, uses
dsthao as an extension-header offset. These fields must not be stale.

For NF_INET_INGRESS, clear the address-family-specific control block and
restore its input interface before constructing the ICMP error.  This
matches similar initialization normally performed by ip_rcv_core() and
ip6_rcv_core().

Fixes: 117ca1f892 ("netfilter: nft_reject_inet: allow to use reject from inet ingress")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.6-sol Codex:gpt-5.5-cyber
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Co-developed-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Kyle Zeng 2026-10-07 23:01:00 +02:00 committed by Pablo Neira Ayuso
parent c203ecf905
commit 73a73d442f
2 changed files with 10 additions and 0 deletions
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5
net/ipv4/netfilter/nf_reject_ipv4.c
View File

@ -357,6 +357,11 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
if (!skb_valid_dst(skb_in) && nf_reject_fill_skb_dst(skb_in) < 0)
return;
if (hook == NF_INET_INGRESS) {
memset(IPCB(skb_in), 0, sizeof(*IPCB(skb_in)));
IPCB(skb_in)->iif = skb_in->skb_iif;
}
if (skb_csum_unnecessary(skb_in) ||
!nf_reject_verify_csum(skb_in, dataoff, proto)) {
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);

5
net/ipv6/netfilter/nf_reject_ipv6.c
View File

@ -444,6 +444,11 @@ void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
skb_in->dev = net->loopback_dev;
if (hooknum == NF_INET_INGRESS) {
memset(IP6CB(skb_in), 0, sizeof(*IP6CB(skb_in)));
IP6CB(skb_in)->iif = skb_in->skb_iif;
}
if (!skb_valid_dst(skb_in) && nf_reject6_fill_skb_dst(skb_in) < 0)
return;