[PATCH v5 1/1] security: Add mechanism to safely (un)load LSMs after boot time

Sargun Dhillon sargun at sargun.me
Mon Apr 9 04:21:41 UTC 2018

On Sun, Apr 8, 2018 at 8:38 PM, Tetsuo Handa
<penguin-kernel at i-love.sakura.ne.jp> wrote:
> Suggested changes on top of your patch:
>   Replace "struct hlist_head *head" in "struct security_hook_list" with
>   "const unsigned int offset" because there is no need to initialize with
>   address of the immutable/mutable chains.
>   Remove LSM_HOOK_INIT_MUTABLE() by embedding just offset (in bytes) from
>   head of "struct security_hook_heads" into "struct security_hook_list"->offset.
>   Make "struct security_hook_heads security_hook_heads" and
>   "struct security_hook_heads security_hook_heads_mutable" local variables.
>   Rename "struct security_hook_heads security_hook_heads" to
>   "struct security_hook_heads security_mutable_hook_heads" and mark it as
>   __ro_after_init.
>   Add the fourth argument to security_add_hooks() which specifies to which
>   chain (security_{mutable|immutable}_hook_heads) to connect.
>   Make all built-in LSM modules (except SELinux if
>   security_immutable_hook_heads.
>   Rename __lsm_ro_after_init to __selinux_ro_after_init which is local to
>   SELinux.
>   Mark "struct security_hook_list"->hook const because it won't change.
>   Mark "struct security_hook_list"->lsm const because none of
>   security_add_hooks() callers are ready to modify the third argument.
>   Remove SECURITY_HOOK_COUNT and "struct security_hook_list"->owner and
>   the exception in randomize_layout_plugin.c because preventing module
>   unloading won't work as expected.

Rather than completely removing the unloading code, might it make
sense to add a BUG_ON or WARN_ON, in security_delete_hooks if
allow_unload_module is false, and owner is not NULL?
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