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, 6 insertions, 1 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 6c463c80e93d..3d32513d6c73 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1679,9 +1679,12 @@ static __latent_entropy struct task_struct *copy_process(
                 goto bad_fork_cleanup_perf;
         /* copy all the process information */
         shm_init_task(p);
-        retval = copy_semundo(clone_flags, p);
+        retval = security_task_alloc(p, clone_flags);
         if (retval)
                 goto bad_fork_cleanup_audit;
+        retval = copy_semundo(clone_flags, p);
+        if (retval)
+                goto bad_fork_cleanup_security;
         retval = copy_files(clone_flags, p);
         if (retval)
                 goto bad_fork_cleanup_semundo;
@@ -1903,6 +1906,8 @@ bad_fork_cleanup_files:
         exit_files(p); /* blocking */
 bad_fork_cleanup_semundo:
         exit_sem(p);
+bad_fork_cleanup_security:
+        security_task_free(p);
 bad_fork_cleanup_audit:
         audit_free(p);
 bad_fork_cleanup_perf: