linux-kernel - Re: [PATCH 1/1] audit_alloc: clear TIF_SYSCALL_AUDIT if !audit

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Message-ID: <CAGXu5jKuSp=c94xAQzdG4QenXnWs0X2n+jCyQb0b1Ncp6tbRMg@mail.gmail.com>
Date:	Wed, 7 Aug 2013 11:53:50 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Eric Paris <eparis@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zach Levis <zml@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] audit_alloc: clear TIF_SYSCALL_AUDIT if !audit_context

On Wed, Aug 7, 2013 at 11:05 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> If audit_filter_task() nacks the new thread it makes sense
> to clear TIF_SYSCALL_AUDIT which can be copied from parent
> by dup_task_struct().
>
> A wrong TIF_SYSCALL_AUDIT is not really bad, but it triggers
> the "slow" audit paths in entry.S.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/auditsc.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 9845cb3..95293ab 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -943,8 +943,10 @@ int audit_alloc(struct task_struct *tsk)
>                 return 0; /* Return if not auditing. */
>
>         state = audit_filter_task(tsk, &key);
> -       if (state == AUDIT_DISABLED)
> +       if (state == AUDIT_DISABLED) {
> +               clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
>                 return 0;
> +       }
>
>         if (!(context = audit_alloc_context(state))) {
>                 kfree(key);
> --
> 1.5.5.1
>
>

Interestingly, I see no other callers of "clear_tsk_thread_flag(tsk,
TIF_SYSCALL_AUDIT)" :)

This patch seems right, since TIF_SYSCALL_AUDIT is set only when
audit_filter_task != AUDIT_DISABLED. Though maybe this should be
explicitly handled in dup_task_struct()?

-Kees

-- 
Kees Cook
Chrome OS Security
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