From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Eric Biggers <ebiggers@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 6.1 376/481] net/tcp-md5: Fix MAC comparison to be constant-time
Date: Mon, 23 Mar 2026 14:45:58 +0100
Message-ID: <20260323134534.296568656@linuxfoundation.org>
In-Reply-To: <20260323134525.256603107@linuxfoundation.org>
References: <20260323134525.256603107@linuxfoundation.org>
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6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@kernel.org>

commit 46d0d6f50dab706637f4c18a470aac20a21900d3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp.c      |    3 ++-
 net/ipv4/tcp_ipv4.c |    3 ++-
 net/ipv6/tcp_ipv6.c |    3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -243,6 +243,7 @@
 
 #define pr_fmt(fmt) "TCP: " fmt
 
+#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -4680,7 +4681,7 @@ tcp_inbound_md5_hash(const struct sock *
 							 hash_expected,
 							 NULL, skb);
 
-	if (genhash || memcmp(hash_location, newhash, 16) != 0) {
+	if (genhash || crypto_memneq(hash_location, newhash, 16)) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMD5FAILURE);
 		if (family == AF_INET) {
 			net_info_ratelimited("MD5 Hash failed for (%pI4, %d)->(%pI4, %d)%s L3 index %d\n",
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -78,6 +78,7 @@
 #include <linux/inetdevice.h>
 #include <linux/btf_ids.h>
 
+#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <linux/scatterlist.h>
 
@@ -776,7 +777,7 @@ static void tcp_v4_send_reset(const stru
 
 
 		genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
-		if (genhash || memcmp(hash_location, newhash, 16) != 0)
+		if (genhash || crypto_memneq(hash_location, newhash, 16))
 			goto out;
 
 	}
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -63,6 +63,7 @@
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 
+#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <linux/scatterlist.h>
 
@@ -1042,7 +1043,7 @@ static void tcp_v6_send_reset(const stru
 			goto out;
 
 		genhash = tcp_v6_md5_hash_skb(newhash, key, NULL, skb);
-		if (genhash || memcmp(hash_location, newhash, 16) != 0)
+		if (genhash || crypto_memneq(hash_location, newhash, 16))
 			goto out;
 	}
 #endif