lkml.org 
[lkml]   [2017]   [May]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2] LSM: Enable multiple calls to security_add_hooks() for the same LSM
From
Date

On 10/05/2017 01:35, Kees Cook wrote:
> On Tue, May 9, 2017 at 4:08 PM, Mickaël Salaün <mic@digikod.net> 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@digikod.net>
>> Cc: Casey Schaufler <casey@schaufler-ca.com>
>> Cc: James Morris <james.l.morris@oracle.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Serge E. Hallyn <serge@hallyn.com>
>> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
>> Link: https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com
>> ---
>> security/security.c | 30 ++++++++++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>>
>> diff --git a/security/security.c b/security/security.c
>> index 549bddcc2116..6be65050b268 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 +87,32 @@ static int __init choose_lsm(char *str)
>> }
>> __setup("security=", choose_lsm);
>>
>> +static bool match_last_lsm(const char *list, const char *last)
>> +{
>> + size_t list_len, last_len, i;
>> +
>> + if (!list || !last)
>> + return false;
>> + list_len = strlen(list);
>> + last_len = strlen(last);
>> + if (!last_len || !list_len)
>> + return false;
>> + if (last_len > list_len)
>> + return false;
>> +
>> + for (i = 0; i < last_len; i++) {
>> + if (list[list_len - 1 - i] != last[last_len - 1 - i])
>> + return false;
>> + }
>> + /* Check if last_len == list_len */
>> + if (i == list_len)
>> + return true;
>> + /* Check if it is a full name */
>> + if (list[list_len - 1 - i] == ',')
>> + return true;
>> + return false;
>> +}
>
> This could be reduced to just:
>
> static bool match_last_lsm(const char *list, const char *lsm)
> {
> char *last;
>
> last = strrchr(list, ',') ?: list;
>
> return (strcmp(last, lsm) == 0);
> }

Indeed, almost the same, I just need to increment and check "last" to
make it work. :)
I'll keep the initial NULL checks, wrap them with a WARN_ON() and use a
const "last", though. It will be much more readable, thanks!

>
>> +
>> static int lsm_append(char *new, char **result)
>> {
>> char *cp;
>> @@ -93,6 +120,9 @@ 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;
>> --
>> 2.11.0
>>
>
>
>

[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2017-05-10 21:20    [W:0.036 / U:34.740 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site