LSM: Revive security_task_alloc() hook and per "struct task_struct" security blob.

We switched from "struct task_struct"->security to "struct cred"->security
in Linux 2.6.29. But not all LSM modules were happy with that change.
TOMOYO LSM module is an example which want to use per "struct task_struct"
security blob, for TOMOYO's security context is defined based on "struct
task_struct" rather than "struct cred". AppArmor LSM module is another
example which want to use it, for AppArmor is currently abusing the cred
a little bit to store the change_hat and setexeccon info. Although
security_task_free() hook was revived in Linux 3.4 because Yama LSM module
wanted to release per "struct task_struct" security blob,
security_task_alloc() hook and "struct task_struct"->security field were
not revived. Nowadays, we are getting proposals of lightweight LSM modules
which want to use per "struct task_struct" security blob.

We are already allowing multiple concurrent LSM modules (up to one fully
armored module which uses "struct cred"->security field or exclusive hooks
like security_xfrm_state_pol_flow_match(), plus unlimited number of
lightweight modules which do not use "struct cred"->security nor exclusive
hooks) as long as they are built into the kernel. But this patch does not
implement variable length "struct task_struct"->security field which will
become needed when multiple LSM modules want to use "struct task_struct"->
security field. Although it won't be difficult to implement variable length
"struct task_struct"->security field, let's think about it after we merged
this patch.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Tested-by: Djalal Harouni <tixxdz@gmail.com>
Acked-by: José Bollo <jobol@nonadev.net>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: James Morris <james.l.morris@oracle.com>
Cc: José Bollo <jobol@nonadev.net>
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/security/security.c b/security/security.c
index 2f15488dc6bc..549bddcc2116 100644
--- a/security/security.c
+++ b/security/security.c
@@ -937,6 +937,11 @@ int security_task_create(unsigned long clone_flags)
 	return call_int_hook(task_create, 0, clone_flags);
 }
 
+int security_task_alloc(struct task_struct *task, unsigned long clone_flags)
+{
+	return call_int_hook(task_alloc, 0, task, clone_flags);
+}
+
 void security_task_free(struct task_struct *task)
 {
 	call_void_hook(task_free, task);