linux-kernel - Re: [PATCH] audit: Call tty_audit_push_task() outside preempt disabled region

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Message-ID: <20091201182202.GA12754@redhat.com>
Date:	Tue, 1 Dec 2009 19:22:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Christoph Hellwig <hch@...radead.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	James Morris <jmorris@...ei.org>
Subject: Re: [PATCH] audit: Call tty_audit_push_task() outside preempt
	disabled region

On 12/01, Thomas Gleixner wrote:
>
> -void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
> +int tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
>  {
> -	struct tty_audit_buf *buf;
> +	struct tty_audit_buf *buf = NULL;
> +	unsigned long flags;
>
> -	spin_lock_irq(&tsk->sighand->siglock);
> -	buf = tsk->signal->tty_audit_buf;
> -	if (buf)
> +	if (!lock_task_sighand(tsk, &flags))
> +		return -ESRCH;
> +
> +	if (tsk->signal->audit_tty && tsk->signal->tty_audit_buf) {
> +		buf = tsk->signal->tty_audit_buf;
>  		atomic_inc(&buf->count);
> -	spin_unlock_irq(&tsk->sighand->siglock);
> +	}
> +	unlock_task_sighand(tsk, &flags);
> +
>  	if (!buf)
> -		return;
> +		return -EPERM;

I think the patch is correct, but it changes the behaviour of
audit_prepare_user_tty() a bit.

Suppose that signal->audit_tty != NULL but signal->tty_audit_buf
is not allocated yet. In this audit_prepare_user_tty() returns 0
before the patch and -EPERM after.

I do not know if this matters, just to be sure this is OK.

Oleg.

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