FAILED: patch "[PATCH] cipso: fix optlen corruption in cipso_v4_delopt()" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] cipso: fix optlen corruption in cipso_v4_delopt()" 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 1f1f8e8c5176234fa31858cd25f2e9b88aac0a45
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109202130-failed-5.15-1f1f8e8c5176@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

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

From 1f1f8e8c5176234fa31858cd25f2e9b88aac0a45 Mon Sep 17 00:00:00 2001
From: Qihang <q.h.hack.winter@gmail.com>
Date: Thu, 29 Oct 2026 11:39:42 +0800
Subject: [PATCH] cipso: fix optlen corruption in cipso_v4_delopt()

cipso_v4_delopt() recomputes the option length by walking the option
buffer after the CIPSO option has been moved out.  The walk then reads
the stale bytes at the tail of the buffer as option data, and a crafted
setsockopt(IP_OPTIONS) buffer can make it treat one of them as an option
length, increasing opt->opt.optlen beyond the valid option data.

The corrupted length stays on the socket and is later used as the copy
length by getsockopt(IP_OPTIONS) and by the udp/raw/ping sendmsg paths,
where it exceeds the size of the buffers they copy into.

Compute the new length from the intact options before the move and
subtract the CIPSO length, and fill the padding with IPOPT_END.

Assisted-by: LLM
Fixes: 014ab19a69c32 ("selinux: Set socket NetLabel based on connection endpoint")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <q.h.hack.winter@gmail.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Dave Miller <davem@davem-thinkpadp1gen8.ibmlond.csb>
---
 net/ipv4/cipso_ipv4.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 1aacbbeffbc64..e65a3f29d2caf 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -2013,6 +2013,10 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		cipso_ptr = &opt->opt.__data[cipso_off];
 		cipso_len = cipso_ptr[1];
 
+		optlen_new = cipso_v4_get_actual_opt_len(opt->opt.__data,
+							 opt->opt.optlen);
+		optlen_new -= cipso_len;
+
 		if (opt->opt.srr > opt->opt.cipso)
 			opt->opt.srr -= cipso_len;
 		if (opt->opt.rr > opt->opt.cipso)
@@ -2026,11 +2030,12 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		memmove(cipso_ptr, cipso_ptr + cipso_len,
 			opt->opt.optlen - cipso_off - cipso_len);
 
-		optlen_new = cipso_v4_get_actual_opt_len(opt->opt.__data,
-							 opt->opt.optlen);
 		hdr_delta = opt->opt.optlen;
 		opt->opt.optlen = (optlen_new + 3) & ~3;
 		hdr_delta -= opt->opt.optlen;
+
+		memset(&opt->opt.__data[optlen_new], IPOPT_END,
+		       opt->opt.optlen - optlen_new);
 	} else {
 		/* only the cipso option was present on the socket so we can
 		 * remove the entire option struct */
-- 
2.53.0

[PATCH 5.15.y 1/2] cipso: make cipso_v4_skbuff_delattr() fully remove the CIPSO options

[Sasha Levin]

From: Ondrej Mosnacek <omosnace@redhat.com>

[ Upstream commit 89aa3619d141d6cfb6040a561aebb6d99d3e2285 ]

As the comment in this function says, the code currently just clears the
CIPSO part with IPOPT_NOP, rather than removing it completely and
trimming the packet. The other cipso_v4_*_delattr() functions, however,
do the proper removal and also calipso_skbuff_delattr() makes an effort
to remove the CALIPSO options instead of replacing them with padding.

Some routers treat IPv4 packets with anything (even NOPs) in the option
header as a special case and take them through a slower processing path.
Consequently, hardening guides such as STIG recommend to configure such
routers to drop packets with non-empty IP option headers [1][2]. Thus,
users might expect NetLabel to produce packets with minimal padding (or
at least with no padding when no actual options are present).

Implement the proper option removal to address this and to be closer to
what the peer functions do.

[1] https://www.stigviewer.com/stig/juniper_router_rtr/2019-09-27/finding/V-90937
[2] https://www.stigviewer.com/stig/cisco_ios_xe_router_rtr/2021-03-26/finding/V-217001

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 1f1f8e8c5176 ("cipso: fix optlen corruption in cipso_v4_delopt()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/cipso_ipv4.c | 79 +++++++++++++++++++++++++++++--------------
 1 file changed, 54 insertions(+), 25 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 016ebcbc8a633..4d4600de92e91 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1813,6 +1813,29 @@ static int cipso_v4_genopt(unsigned char *buf, u32 buf_len,
 	return CIPSO_V4_HDR_LEN + ret_val;
 }
 
+static int cipso_v4_get_actual_opt_len(const unsigned char *data, int len)
+{
+	int iter = 0, optlen = 0;
+
+	/* determining the new total option length is tricky because of
+	 * the padding necessary, the only thing i can think to do at
+	 * this point is walk the options one-by-one, skipping the
+	 * padding at the end to determine the actual option size and
+	 * from there we can determine the new total option length
+	 */
+	while (iter < len) {
+		if (data[iter] == IPOPT_END) {
+			break;
+		} else if (data[iter] == IPOPT_NOP) {
+			iter++;
+		} else {
+			iter += data[iter + 1];
+			optlen = iter;
+		}
+	}
+	return optlen;
+}
+
 /**
  * cipso_v4_sock_setattr - Add a CIPSO option to a socket
  * @sk: the socket
@@ -1988,7 +2011,6 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		u8 cipso_len;
 		u8 cipso_off;
 		unsigned char *cipso_ptr;
-		int iter;
 		int optlen_new;
 
 		cipso_off = opt->opt.cipso - sizeof(struct iphdr);
@@ -2008,23 +2030,8 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		memmove(cipso_ptr, cipso_ptr + cipso_len,
 			opt->opt.optlen - cipso_off - cipso_len);
 
-		/* determining the new total option length is tricky because of
-		 * the padding necessary, the only thing i can think to do at
-		 * this point is walk the options one-by-one, skipping the
-		 * padding at the end to determine the actual option size and
-		 * from there we can determine the new total option length */
-		iter = 0;
-		optlen_new = 0;
-		while (iter < opt->opt.optlen) {
-			if (opt->opt.__data[iter] == IPOPT_END) {
-				break;
-			} else if (opt->opt.__data[iter] == IPOPT_NOP) {
-				iter++;
-			} else {
-				iter += opt->opt.__data[iter + 1];
-				optlen_new = iter;
-			}
-		}
+		optlen_new = cipso_v4_get_actual_opt_len(opt->opt.__data,
+							 opt->opt.optlen);
 		hdr_delta = opt->opt.optlen;
 		opt->opt.optlen = (optlen_new + 3) & ~3;
 		hdr_delta -= opt->opt.optlen;
@@ -2244,7 +2251,8 @@ int cipso_v4_skbuff_setattr(struct sk_buff *skb,
  */
 int cipso_v4_skbuff_delattr(struct sk_buff *skb)
 {
-	int ret_val;
+	int ret_val, cipso_len, hdr_len_actual, new_hdr_len_actual, new_hdr_len,
+	    hdr_len_delta;
 	struct iphdr *iph;
 	struct ip_options *opt = &IPCB(skb)->opt;
 	unsigned char *cipso_ptr;
@@ -2257,16 +2265,37 @@ int cipso_v4_skbuff_delattr(struct sk_buff *skb)
 	if (ret_val < 0)
 		return ret_val;
 
-	/* the easiest thing to do is just replace the cipso option with noop
-	 * options since we don't change the size of the packet, although we
-	 * still need to recalculate the checksum */
-
 	iph = ip_hdr(skb);
 	cipso_ptr = (unsigned char *)iph + opt->cipso;
-	memset(cipso_ptr, IPOPT_NOOP, cipso_ptr[1]);
+	cipso_len = cipso_ptr[1];
+
+	hdr_len_actual = sizeof(struct iphdr) +
+			 cipso_v4_get_actual_opt_len((unsigned char *)(iph + 1),
+						     opt->optlen);
+	new_hdr_len_actual = hdr_len_actual - cipso_len;
+	new_hdr_len = (new_hdr_len_actual + 3) & ~3;
+	hdr_len_delta = (iph->ihl << 2) - new_hdr_len;
+
+	/* 1. shift any options after CIPSO to the left */
+	memmove(cipso_ptr, cipso_ptr + cipso_len,
+		new_hdr_len_actual - opt->cipso);
+	/* 2. move the whole IP header to its new place */
+	memmove((unsigned char *)iph + hdr_len_delta, iph, new_hdr_len_actual);
+	/* 3. adjust the skb layout */
+	skb_pull(skb, hdr_len_delta);
+	skb_reset_network_header(skb);
+	iph = ip_hdr(skb);
+	/* 4. re-fill new padding with IPOPT_END (may now be longer) */
+	memset((unsigned char *)iph + new_hdr_len_actual, IPOPT_END,
+	       new_hdr_len - new_hdr_len_actual);
+
+	opt->optlen -= hdr_len_delta;
 	opt->cipso = 0;
 	opt->is_changed = 1;
-
+	if (hdr_len_delta != 0) {
+		iph->ihl = new_hdr_len >> 2;
+		iph_set_totlen(iph, skb->len);
+	}
 	ip_send_check(iph);
 
 	return 0;
-- 
2.53.0

[PATCH 5.15.y 2/2] cipso: fix optlen corruption in cipso_v4_delopt()

[Sasha Levin]

From: Qihang <q.h.hack.winter@gmail.com>

[ Upstream commit 1f1f8e8c5176234fa31858cd25f2e9b88aac0a45 ]

cipso_v4_delopt() recomputes the option length by walking the option
buffer after the CIPSO option has been moved out.  The walk then reads
the stale bytes at the tail of the buffer as option data, and a crafted
setsockopt(IP_OPTIONS) buffer can make it treat one of them as an option
length, increasing opt->opt.optlen beyond the valid option data.

The corrupted length stays on the socket and is later used as the copy
length by getsockopt(IP_OPTIONS) and by the udp/raw/ping sendmsg paths,
where it exceeds the size of the buffers they copy into.

Compute the new length from the intact options before the move and
subtract the CIPSO length, and fill the padding with IPOPT_END.

Assisted-by: LLM
Fixes: 014ab19a69c32 ("selinux: Set socket NetLabel based on connection endpoint")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <q.h.hack.winter@gmail.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Dave Miller <davem@davem-thinkpadp1gen8.ibmlond.csb>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/cipso_ipv4.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 4d4600de92e91..13f2e7f0531d9 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -2017,6 +2017,10 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		cipso_ptr = &opt->opt.__data[cipso_off];
 		cipso_len = cipso_ptr[1];
 
+		optlen_new = cipso_v4_get_actual_opt_len(opt->opt.__data,
+							 opt->opt.optlen);
+		optlen_new -= cipso_len;
+
 		if (opt->opt.srr > opt->opt.cipso)
 			opt->opt.srr -= cipso_len;
 		if (opt->opt.rr > opt->opt.cipso)
@@ -2030,11 +2034,12 @@ static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 		memmove(cipso_ptr, cipso_ptr + cipso_len,
 			opt->opt.optlen - cipso_off - cipso_len);
 
-		optlen_new = cipso_v4_get_actual_opt_len(opt->opt.__data,
-							 opt->opt.optlen);
 		hdr_delta = opt->opt.optlen;
 		opt->opt.optlen = (optlen_new + 3) & ~3;
 		hdr_delta -= opt->opt.optlen;
+
+		memset(&opt->opt.__data[optlen_new], IPOPT_END,
+		       opt->opt.optlen - optlen_new);
 	} else {
 		/* only the cipso option was present on the socket so we can
 		 * remove the entire option struct */
-- 
2.53.0