[Pam-developers] [PATCH] pam_loginuid: return PAM_IGNORE when /proc/self/loginuid does not exist

Steve Langasek vorlon at debian.org
Fri Jan 10 08:11:03 UTC 2014


On Thu, Jan 09, 2014 at 05:41:02AM +0400, Dmitry V. Levin wrote:
> Hi Steve,

> On Wed, Jan 08, 2014 at 04:09:39PM -0800, Steve Langasek wrote:
> > On Wed, Jan 08, 2014 at 05:16:32AM +0400, Dmitry V. Levin wrote:
> [...]
> > > * modules/pam_loginuid/pam_loginuid.c (set_loginuid): Change return
> > > code semantics: return PAM_SUCCESS on success, PAM_IGNORE when loginuid
> > > does not exist, PAM_SESSION_ERR in case of any other error.
> > > (_pam_loginuid): Forward the PAM error code returned by set_loginuid.
> > 
> > Thanks, looks good.  The only thing I have a question on is whether it makes
> > sense to still call require_auditd() in any cases that setting the loginuid
> > failed.  Maybe this should be implicitly ignored?

> It doesn't look reasonable to me either, but there might be some less
> obvious use case for require_auditd option I'm not aware of.

> > Anyway, the current behavior fails closed, so that should be fine for a
> > first pass - and if somebody is concerned about setting "require_auditd" in
> > a pam config that's being used in an unprivileged container, we can always
> > revisit later.

> Agreed.

> > So, +1 from me - and attached is the rebased for userns support.

> I'm not quite familiar with uid_map semantics yet;
> can we assume that host's uid_map will remain the same?
> If yes, then the change is OK, although I'd tweak it a bit:

Agreed with these tweaks.  I'll go ahead and commit this.

Thanks,
-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org

> --- a/modules/pam_loginuid/pam_loginuid.c
> +++ b/modules/pam_loginuid/pam_loginuid.c
> @@ -55,7 +55,8 @@ static int set_loginuid(pam_handle_t *pamh, uid_t uid)
>  {
>  	int fd, count, rc = PAM_SESSION_ERR;
>  	char loginuid[24], buf[24];
> -	char uid_map[256];
> +	static const char host_uid_map[] = "         0          0 4294967295\n";
> +	char uid_map[sizeof(host_uid_map)];
>  
>  	count = snprintf(loginuid, sizeof(loginuid), "%lu", (unsigned long)uid);
>  	fd = open("/proc/self/loginuid", O_NOFOLLOW|O_RDWR);
> @@ -66,15 +67,14 @@ static int set_loginuid(pam_handle_t *pamh, uid_t uid)
>  			fd = open("/proc/self/uid_map", O_RDONLY);
>  			if (fd >= 0) {
>  				count = pam_modutil_read(fd, uid_map, sizeof(uid_map));
> -				if (strncmp(uid_map, "         0          0 4294967295\n",
> -				    count) != 0)
> +				if (strncmp(uid_map, host_uid_map, count) != 0)
>  					rc = PAM_IGNORE;
>  				close(fd);
>  			}
>  			if (rc != PAM_IGNORE)
> -				pam_syslog(pamh, LOG_ERR,
> -					   "Cannot open /proc/self/loginuid: Permission denied");
> -		} else {
> +				errno = EACCES;
> +		}
> +		if (rc != PAM_IGNORE) {
>  			pam_syslog(pamh, LOG_ERR,
>  				   "Cannot open /proc/self/loginuid: %m");
>  		}
> 
> -- 
> ldv



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