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, 8 insertions, 1 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 1aa63335de9e..080f34e66017 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -533,8 +533,13 @@
  *	manual page for definitions of the @clone_flags.
  *	@clone_flags contains the flags indicating what should be shared.
  *	Return 0 if permission is granted.
+ * @task_alloc:
+ *	@task task being allocated.
+ *	@clone_flags contains the flags indicating what should be shared.
+ *	Handle allocation of task-related resources.
+ *	Returns a zero on success, negative values on failure.
  * @task_free:
- *	@task task being freed
+ *	@task task about to be freed.
  *	Handle release of task-related resources. (Note that this can be called
  *	from interrupt context.)
  * @cred_alloc_blank:
@@ -1482,6 +1487,7 @@ union security_list_options {
 	int (*file_open)(struct file *file, const struct cred *cred);
 
 	int (*task_create)(unsigned long clone_flags);
+	int (*task_alloc)(struct task_struct *task, unsigned long clone_flags);
 	void (*task_free)(struct task_struct *task);
 	int (*cred_alloc_blank)(struct cred *cred, gfp_t gfp);
 	void (*cred_free)(struct cred *cred);
@@ -1748,6 +1754,7 @@ struct security_hook_heads {
 	struct list_head file_receive;
 	struct list_head file_open;
 	struct list_head task_create;
+	struct list_head task_alloc;
 	struct list_head task_free;
 	struct list_head cred_alloc_blank;
 	struct list_head cred_free;