From: Eric Biggers ebiggers@kernel.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@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@kernel.org Reviewed-by: Andrea Mayer andrea.mayer@uniroma2.it Link: https://patch.msgid.link/20250818202724.15713-1-ebiggers@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [Andrey Troshin: backport fix for 5.10] Signed-off-by: Andrey Troshin drtrosh@yandex-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;