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SubjectRe: [PATCH v1] LSM: Enable multiple calls to security_add_hooks() for the same LSM
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On 4/29/2017 12:02 PM, Mickaël Salaün wrote:
> Check if the registering LSM already registered hooks just before. This
> enable to split hook declarations into multiple files without
> registering multiple time the same LSM name, starting from commit
> d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm").

What's special about the previous registration? Keep it
simple and check it the name is already anywhere on the
list and only add it if it's not already there. I don't
see advantage to:

% cat /sys/kernel/security/lsm
capability,yama,spiffy,selinux,spiffy

over
% cat /sys/kernel/security/lsm
capability,yama,spiffy,selinux

>
> 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>
> 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;
> +}
> +
> 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;

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