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net/tcp-md5: Fix MAC comparison to be constant-time

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

Fixes: cfb6eeb4c8 ("[TCP]: MD5 Signature Option (RFC2385) support.")
Fixes: 658ddaaf66 ("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>
This commit is contained in:
Eric Biggers 2026-03-02 12:34:09 -08:00 • committed by Jakub Kicinski
parent 7f5d8e63f3
commit 46d0d6f50d
4 changed files with 7 additions and 3 deletions
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1
net/ipv4/Kconfig
View file

@ -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

3
net/ipv4/tcp.c
View file

@ -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;

3
net/ipv4/tcp_ipv4.c
View file

@ -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;
}

3
net/ipv6/tcp_ipv6.c
View file

@ -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