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SubjectRe: [PATCH v3] LSM: Enable multiple calls to security_add_hooks() for the same LSM
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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@digikod.net>

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


> 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 | 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;

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