Re: [PATCH 2/2] scsi: target: use constant-time crypto_memneq for CHAP digests

On Fri, Jun 5, 2026 at 5:32 AM David Disseldorp <[email protected]> wrote:
>
> A constant-time memory comparison is more suitable than plain memcmp()
> for authentication digest comparison.
> CHAP digests use an authenticator-provided random challenge, so any
> timing side-channel shouldn't be easily exploitable.
>
> Reported-by: Sashiko (gemini/gemini-3.1-pro-preview)
> Link: https://sashiko.dev/#/patchset/20260521151121.808477-1-hossu.alexandru%40gmail.com
> Signed-off-by: David Disseldorp <[email protected]>
> ---
>  drivers/target/iscsi/iscsi_target_auth.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/target/iscsi/iscsi_target_auth.c b/drivers/target/iscsi/iscsi_target_auth.c
> index 5858cc3089796..f3c0cdd318300 100644
> --- a/drivers/target/iscsi/iscsi_target_auth.c
> +++ b/drivers/target/iscsi/iscsi_target_auth.c
> @@ -9,6 +9,7 @@
>   ******************************************************************************/
>
>  #include <crypto/hash.h>
> +#include <crypto/utils.h>
>  #include <linux/kernel.h>
>  #include <linux/string.h>
>  #include <linux/err.h>
> @@ -408,7 +409,7 @@ static int chap_server_compute_hash(
>         pr_debug("[server] %s Server Digest: %s\n",
>                 chap->digest_name, response);
>
> -       if (memcmp(server_digest, client_digest, chap->digest_size) != 0) {
> +       if (crypto_memneq(server_digest, client_digest, chap->digest_size)) {
>                 pr_debug("[server] %s Digests do not match!\n\n",
>                         chap->digest_name);
>                 goto out;
> --
> 2.51.0
>
>

Reviewed-by: Lee Duncan <[email protected]>