linux-kernel - Re: [PATCH v3] LSM: Enable multiple calls to security_add

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <dff4cd49-bf3e-ddcc-003d-1c624c2c8d7e@schaufler-ca.com>
Date:   Wed, 10 May 2017 15:26:35 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        linux-kernel@...r.kernel.org
Cc:     James Morris <james.l.morris@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v3] LSM: Enable multiple calls to security_add_hooks() for
 the same LSM

On 5/10/2017 1:48 PM, Mickaël Salaün wrote:
> The commit d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm") extend
> security_add_hooks() with a new parameter to register the LSM name,
> which may be useful to make the list of currently loaded LSM available
> to userspace. However, there is no clean way for an LSM to split its
> hook declarations into multiple files, which may reduce the mess with
> all the included files (needed for LSM hook argument types) and make the
> source code easier to review and maintain.
>
> This change allows an LSM to register multiple times its hook while
> keeping a consistent list of LSM names as described in
> Documentation/security/LSM.txt . The list reflects the order in which
> checks are made. This patch only check for the last registered LSM. If
> an LSM register multiple times its hooks, interleaved with other LSM
> registrations (which should not happen), its name will still appear in
> the same order that the hooks are called, hence multiple times.
>
> To sum up, "capability,selinux,foo,foo" will be replaced with
> "capability,selinux,foo", however "capability,foo,selinux,foo" will
> remain as is.
>
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>

Acked-by: Casey Schaufler <casey@...aufler-ca.com>
 

> Cc: Casey Schaufler <casey@...aufler-ca.com>
> Cc: James Morris <james.l.morris@...cle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
> Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Link: https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com
> ---
>  security/security.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/security/security.c b/security/security.c
> index 549bddcc2116..54b1e395978a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -25,6 +25,7 @@
>  #include <linux/mount.h>
>  #include <linux/personality.h>
>  #include <linux/backing-dev.h>
> +#include <linux/string.h>
>  #include <net/flow.h>
>  
>  #define MAX_LSM_EVM_XATTR	2
> @@ -86,6 +87,21 @@ static int __init choose_lsm(char *str)
>  }
>  __setup("security=", choose_lsm);
>  
> +static bool match_last_lsm(const char *list, const char *lsm)
> +{
> +	const char *last;
> +
> +	if (WARN_ON(!list || !lsm))
> +		return false;
> +	last = strrchr(list, ',');
> +	if (last)
> +		/* Pass the comma, strcmp() will check for '\0' */
> +		last++;
> +	else
> +		last = list;
> +	return !strcmp(last, lsm);
> +}
> +
>  static int lsm_append(char *new, char **result)
>  {
>  	char *cp;
> @@ -93,6 +109,9 @@ static int lsm_append(char *new, char **result)
>  	if (*result == NULL) {
>  		*result = kstrdup(new, GFP_KERNEL);
>  	} else {
> +		/* Check if it is the last registered name */
> +		if (match_last_lsm(*result, new))
> +			return 0;
>  		cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
>  		if (cp == NULL)
>  			return -ENOMEM;