FAILED: patch "[PATCH] net/tcp-md5: Fix MAC comparison to be constant-time" failed to apply to 6.18-stable tree

FAILED: patch "[PATCH] net/tcp-md5: Fix MAC comparison to be constant-time" failed to apply to 6.18-stable tree

[gregkh]

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 46d0d6f50dab706637f4c18a470aac20a21900d3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026031756-likewise-lumpiness-6c88@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 46d0d6f50dab706637f4c18a470aac20a21900d3 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@kernel.org>
Date: Mon, 2 Mar 2026 12:34:09 -0800
Subject: [PATCH] net/tcp-md5: Fix MAC comparison to be constant-time

To prevent timing attacks, MACs need to be compared in constant
time.  Use the appropriate helper function for this.

Fixes: cfb6eeb4c860 ("[TCP]: MD5 Signature Option (RFC2385) support.")
Fixes: 658ddaaf6694 ("tcp: md5: RST: getting md5 key from listener")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Link: https://patch.msgid.link/20260302203409.13388-1-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 3ab6247be585..df922f9f5289 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -762,6 +762,7 @@ config TCP_AO
 config TCP_MD5SIG
 	bool "TCP: MD5 Signature Option support (RFC2385)"
 	select CRYPTO_LIB_MD5
+	select CRYPTO_LIB_UTILS
 	help
 	  RFC2385 specifies a method of giving MD5 protection to TCP sessions.
 	  Its main (only?) use is to protect BGP sessions between core routers
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 8cdc26e8ad68..202a4e57a218 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -244,6 +244,7 @@
 #define pr_fmt(fmt) "TCP: " fmt
 
 #include <crypto/md5.h>
+#include <crypto/utils.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/types.h>
@@ -4970,7 +4971,7 @@ tcp_inbound_md5_hash(const struct sock *sk, const struct sk_buff *skb,
 		tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
 	else
 		tp->af_specific->calc_md5_hash(newhash, key, NULL, skb);
-	if (memcmp(hash_location, newhash, 16) != 0) {
+	if (crypto_memneq(hash_location, newhash, 16)) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5FAILURE);
 		trace_tcp_hash_md5_mismatch(sk, skb);
 		return SKB_DROP_REASON_TCP_MD5FAILURE;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d53d39be291a..910c25cb24e1 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -88,6 +88,7 @@
 #include <linux/skbuff_ref.h>
 
 #include <crypto/md5.h>
+#include <crypto/utils.h>
 
 #include <trace/events/tcp.h>
 
@@ -839,7 +840,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb,
 			goto out;
 
 		tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
-		if (memcmp(md5_hash_location, newhash, 16) != 0)
+		if (crypto_memneq(md5_hash_location, newhash, 16))
 			goto out;
 	}
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index e46a0efae012..5195a46b951e 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -68,6 +68,7 @@
 #include <linux/seq_file.h>
 
 #include <crypto/md5.h>
+#include <crypto/utils.h>
 
 #include <trace/events/tcp.h>
 
@@ -1048,7 +1049,7 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb,
 		key.type = TCP_KEY_MD5;
 
 		tcp_v6_md5_hash_skb(newhash, key.md5_key, NULL, skb);
-		if (memcmp(md5_hash_location, newhash, 16) != 0)
+		if (crypto_memneq(md5_hash_location, newhash, 16))
 			goto out;
 	}
 #endif

Re: FAILED: patch "[PATCH] net/tcp-md5: Fix MAC comparison to be constant-time" failed to apply to 6.18-stable tree

[Eric Biggers]

On Tue, Mar 17, 2026 at 01:01:56PM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.18-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>.

I already did this a week earlier.

- Eric

Re: FAILED: patch "[PATCH] net/tcp-md5: Fix MAC comparison to be constant-time" failed to apply to 6.18-stable tree

[Greg KH]

On Wed, Mar 18, 2026 at 09:27:03PM +0000, Eric Biggers wrote:
> On Tue, Mar 17, 2026 at 01:01:56PM +0100, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 6.18-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>.
> 
> I already did this a week earlier.

Sorry bout that, I process them after going through the upstream
patches.  I see that now and will go queue it up.

thanks,

greg k-h