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 <[email protected]>
Acked-by: John Johansen <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Acked-by: Casey Schaufler <[email protected]>
Tested-by: Djalal Harouni <[email protected]>
Acked-by: José Bollo <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: Stephen Smalley <[email protected]>
Cc: Eric Paris <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: James Morris <[email protected]>
Cc: José Bollo <[email protected]>
Signed-off-by: James Morris <[email protected]>

0 files changed, 0 insertions, 0 deletions