FAILED: patch "[PATCH] netfilter: nf_reject: initialize IPCB at inet ingress" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] netfilter: nf_reject: initialize IPCB at inet ingress" failed to apply to 5.15-stable tree

[Sasha Levin]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 73a73d442f9986353fe284bd1b504d0313d0f153
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107060821-failed-5.15-73a73d442f99@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 73a73d442f9986353fe284bd1b504d0313d0f153 Mon Sep 17 00:00:00 2001
From: Kyle Zeng <kylebot@openai.com>
Date: Wed, 7 Oct 2026 23:01:00 +0200
Subject: [PATCH] netfilter: nf_reject: initialize IPCB at inet ingress

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: 117ca1f8920c ("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>
---
 net/ipv4/netfilter/nf_reject_ipv4.c | 5 +++++
 net/ipv6/netfilter/nf_reject_ipv6.c | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 59ec465a9df98..7cb33af671e26 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -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);
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index 07cdaa10da0d0..5e08d8529cc88 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -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;
 
-- 
2.53.0

[PATCH 5.15.y 1/2] netfilter: conntrack: skip verification of zero UDP checksum

[Sasha Levin]

From: Kevin Mitchell <kevmitch@arista.com>

[ Upstream commit 4f9bd53084d18c2f9f1ec68fa56587b99a2cef00 ]

The checksum is optional for UDP packets. However nf_reject would
previously require a valid checksum to elicit a response such as
ICMP_DEST_UNREACH.

Add some logic to nf_reject_verify_csum to determine if a UDP packet has
a zero checksum and should therefore not be verified.

Signed-off-by: Kevin Mitchell <kevmitch@arista.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Stable-dep-of: 73a73d442f99 ("netfilter: nf_reject: initialize IPCB at inet ingress")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/netfilter/nf_reject.h   | 21 +++++++++++++++++----
 net/ipv4/netfilter/nf_reject_ipv4.c | 10 +++++++---
 net/ipv6/netfilter/nf_reject_ipv6.c |  4 ++--
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/include/net/netfilter/nf_reject.h b/include/net/netfilter/nf_reject.h
index 9051c3a0c8e77..7c669792fb9ce 100644
--- a/include/net/netfilter/nf_reject.h
+++ b/include/net/netfilter/nf_reject.h
@@ -5,12 +5,28 @@
 #include <linux/types.h>
 #include <uapi/linux/in.h>
 
-static inline bool nf_reject_verify_csum(__u8 proto)
+static inline bool nf_reject_verify_csum(struct sk_buff *skb, int dataoff,
+					  __u8 proto)
 {
 	/* Skip protocols that don't use 16-bit one's complement checksum
 	 * of the entire payload.
 	 */
 	switch (proto) {
+		/* Protocols with optional checksums. */
+		case IPPROTO_UDP: {
+			const struct udphdr *udp_hdr;
+			struct udphdr _udp_hdr;
+
+			udp_hdr = skb_header_pointer(skb, dataoff,
+						     sizeof(_udp_hdr),
+						     &_udp_hdr);
+			if (!udp_hdr || udp_hdr->check)
+				return true;
+
+			return false;
+		}
+		case IPPROTO_GRE:
+
 		/* Protocols with other integrity checks. */
 		case IPPROTO_AH:
 		case IPPROTO_ESP:
@@ -19,9 +35,6 @@ static inline bool nf_reject_verify_csum(__u8 proto)
 		/* Protocols with partial checksums. */
 		case IPPROTO_UDPLITE:
 		case IPPROTO_DCCP:
-
-		/* Protocols with optional checksums. */
-		case IPPROTO_GRE:
 			return false;
 	}
 	return true;
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index ddfb4e2b779d6..89f52751355bf 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -102,6 +102,7 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
 	struct iphdr *niph;
 	struct icmphdr *icmph;
 	unsigned int len;
+	int dataoff;
 	__wsum csum;
 	u8 proto;
 
@@ -125,10 +126,11 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
 	if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
 		return NULL;
 
+	dataoff = ip_hdrlen(oldskb);
 	proto = ip_hdr(oldskb)->protocol;
 
 	if (!skb_csum_unnecessary(oldskb) &&
-	    nf_reject_verify_csum(proto) &&
+	    nf_reject_verify_csum(oldskb, dataoff, proto) &&
 	    nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
 		return NULL;
 
@@ -338,6 +340,7 @@ EXPORT_SYMBOL_GPL(nf_send_reset);
 void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
 {
 	struct iphdr *iph = ip_hdr(skb_in);
+	int dataoff = ip_hdrlen(skb_in);
 	u8 proto = iph->protocol;
 
 	if (iph->frag_off & htons(IP_OFFSET))
@@ -346,12 +349,13 @@ 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 (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
+	if (skb_csum_unnecessary(skb_in) ||
+	    !nf_reject_verify_csum(skb_in, dataoff, proto)) {
 		icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 		return;
 	}
 
-	if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
+	if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
 		icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 }
 EXPORT_SYMBOL_GPL(nf_send_unreach);
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index 099740342f70f..c5c8962088f2c 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -32,7 +32,7 @@ static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
 	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 		return false;
 
-	if (!nf_reject_verify_csum(proto))
+	if (!nf_reject_verify_csum(skb, thoff, proto))
 		return true;
 
 	return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
@@ -413,7 +413,7 @@ static bool reject6_csum_ok(struct sk_buff *skb, int hook)
 	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 		return false;
 
-	if (!nf_reject_verify_csum(proto))
+	if (!nf_reject_verify_csum(skb, thoff, proto))
 		return true;
 
 	return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
-- 
2.53.0

[PATCH 5.15.y 2/2] netfilter: nf_reject: initialize IPCB at inet ingress

[Sasha Levin]

From: Kyle Zeng <kylebot@openai.com>

[ Upstream commit 73a73d442f9986353fe284bd1b504d0313d0f153 ]

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: 117ca1f8920c ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/netfilter/nf_reject_ipv4.c | 5 +++++
 net/ipv6/netfilter/nf_reject_ipv6.c | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 89f52751355bf..ba5b6cb42e70b 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -349,6 +349,11 @@ 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);
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index c5c8962088f2c..3372658e6d125 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -428,6 +428,11 @@ 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;
 
-- 
2.53.0