From: Stephen Smalley <stephen.smalley.work@gmail.com>
To: cgzones@googlemail.com
Cc: selinux@vger.kernel.org
Subject: Re: [RFC PATCH 1/3] newrole: constant time password comparison
Date: Tue, 9 Apr 2024 13:56:26 -0400 [thread overview]
Message-ID: <CAEjxPJ4MRkgTSjc1uzASZzcvCNgnkcpZW-QHCYU7sMHqVQB8Eg@mail.gmail.com> (raw)
In-Reply-To: <20240408153006.69840-1-cgoettsche@seltendoof.de>
On Mon, Apr 8, 2024 at 11:31 AM Christian Göttsche
<cgoettsche@seltendoof.de> wrote:
>
> From: Christian Göttsche <cgzones@googlemail.com>
>
> Perform the password hash comparison in a time constant way to avoid
> leaking the length of the identical prefix via a side-channel.
> Since only hashes are compared leaking the total length is non critical.
>
> Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Should we just require PAM for newrole and be done with it?
> ---
> policycoreutils/newrole/newrole.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/policycoreutils/newrole/newrole.c b/policycoreutils/newrole/newrole.c
> index 5a1a1129..1e01d2ef 100644
> --- a/policycoreutils/newrole/newrole.c
> +++ b/policycoreutils/newrole/newrole.c
> @@ -338,6 +338,24 @@ static void memzero(void *ptr, size_t size)
> }
> }
>
> +static int streq_constant(const char *userinput, const char *secret)
> +{
> + const volatile char *x = userinput, *y = secret;
> + size_t i, u_len, s_len;
> + int ret = 0;
> +
> + u_len = strlen(userinput);
> + s_len = strlen(secret);
> +
> + if (u_len != s_len)
> + return 0;
> +
> + for (i = 0; i < u_len; i++)
> + ret |= x[i] ^ y[i];
> +
> + return ret == 0;
> +}
> +
> /* authenticate_via_shadow_passwd()
> *
> * in: uname - the calling user's user name
> @@ -383,7 +401,7 @@ static int authenticate_via_shadow_passwd(const char *uname)
> return 0;
> }
>
> - ret = !strcmp(encrypted_password_s, p_shadow_line->sp_pwdp);
> + ret = streq_constant(encrypted_password_s, p_shadow_line->sp_pwdp);
> memzero(encrypted_password_s, strlen(encrypted_password_s));
> return ret;
> }
> --
> 2.43.0
>
>
prev parent reply other threads:[~2024-04-09 17:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-08 15:30 [RFC PATCH 1/3] newrole: constant time password comparison Christian Göttsche
2024-04-08 15:30 ` [RFC PATCH 2/3] newrole: cleanse shadow data hold by libc Christian Göttsche
2024-04-08 15:30 ` [RFC PATCH 3/3] newrole: use ROWHAMMER resistant values Christian Göttsche
2024-04-09 17:56 ` Stephen Smalley [this message]
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