From: Eric Biggers <ebiggers@kernel.org>
Date: Mon, 2 Mar 2026 20:34:09 +0000 (-0800)
Subject: net/tcp-md5: Fix MAC comparison to be constant-time
X-Git-Tag: v7.0-rc3~39^2~26
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=46d0d6f50dab706637f4c18a470aac20a21900d3;p=thirdparty%2Fkernel%2Flinux.git

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