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SubjectRe: [RFC][PATCH 1/4] lsm: Clarify documentation of vm_enough_memory hook
On Tue, Nov 15, 2022 at 12:57 PM Roberto Sassu
<roberto.sassu@huaweicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> include/linux/lsm_hooks.h reports the result of the LSM infrastructure to
> the callers, not what LSMs should return to the LSM infrastructure.
>
> Clarify that and add that returning 1 from the LSMs means calling
> __vm_enough_memory() with cap_sys_admin set, 0 without.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: KP Singh <kpsingh@kernel.org>
> ---
> include/linux/lsm_hooks.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 4ec80b96c22e..f40b82ca91e7 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1411,7 +1411,9 @@
> * Check permissions for allocating a new virtual mapping.
> * @mm contains the mm struct it is being added to.
> * @pages contains the number of pages.
> - * Return 0 if permission is granted.
> + * Return 0 if permission is granted by LSMs to the caller. LSMs should
> + * return 1 if __vm_enough_memory() should be called with
> + * cap_sys_admin set, 0 if not.

I think this is a nice addition, but according to the code, any value
greater than zero will trigger the caller-should-have-CAP_SYS_ADMIN
behavior, not just 1. I suggest updating the comment.

--
paul-moore.com

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