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 <m...@digikod.net>Acked-by: Casey Schaufler <ca...@schaufler-ca.com> > Cc: Casey Schaufler <ca...@schaufler-ca.com> > Cc: James Morris <james.l.mor...@oracle.com> > Cc: Kees Cook <keesc...@chromium.org> > Cc: Serge E. Hallyn <se...@hallyn.com> > Cc: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > Link: > https://lkml.kernel.org/r/ccad825b-7a58-e499-e51b-bd7c98581...@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;
