linux-kernel - [PATCH 5.10] ipv6: sr: Fix MAC comparison to be constant-time

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Message-ID: <20251028142755.2059-1-drtrosh@yandex-team.ru>
Date: Tue, 28 Oct 2025 17:27:55 +0300
From: Andrey Troshin <drtrosh@...dex-team.ru>
To: stable@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Andrey Troshin <drtrosh@...dex-team.ru>,
	"David S . Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Jakub Kicinski <kuba@...nel.org>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 5.10] ipv6: sr: Fix MAC comparison to be constant-time

From: Eric Biggers <ebiggers@...nel.org>

commit a458b2902115b26a25d67393b12ddd57d1216aaa upstream.

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

Fixes: bf355b8d2c30 ("ipv6: sr: add core files for SR HMAC support")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...nel.org>
Reviewed-by: Andrea Mayer <andrea.mayer@...roma2.it>
Link: https://patch.msgid.link/20250818202724.15713-1-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[Andrey Troshin: backport fix for 5.10]
Signed-off-by: Andrey Troshin <drtrosh@...dex-team.ru>
---
Backport fix for CVE-2025-39702
Link: https://nvd.nist.gov/vuln/detail/CVE-2025-39702
---
 net/ipv6/seg6_hmac.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/seg6_hmac.c b/net/ipv6/seg6_hmac.c
index 4a3f7bb027ed..8bb7f94cba1e 100644
--- a/net/ipv6/seg6_hmac.c
+++ b/net/ipv6/seg6_hmac.c
@@ -35,6 +35,7 @@
 #include <net/xfrm.h>
 
 #include <crypto/hash.h>
+#include <crypto/algapi.h>
 #include <crypto/sha.h>
 #include <net/seg6.h>
 #include <net/genetlink.h>
@@ -270,7 +271,7 @@ bool seg6_hmac_validate_skb(struct sk_buff *skb)
 	if (seg6_hmac_compute(hinfo, srh, &ipv6_hdr(skb)->saddr, hmac_output))
 		return false;
 
-	if (memcmp(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN) != 0)
+	if (crypto_memneq(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN))
 		return false;
 
 	return true;
-- 
2.34.1