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Date: Tue, 1 Dec 2009 19:22:02 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Christoph Hellwig <hch@infradead.org>, Nick Piggin <npiggin@suse.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Al Viro <viro@zeniv.linux.org.uk>, James Morris <jmorris@namei.org>
Subject: Re: [PATCH] audit: Call tty_audit_push_task() outside preempt
	disabled region
Message-ID: <20091201182202.GA12754@redhat.com>
References: <20091130100041.GA29610@infradead.org> <alpine.LFD.2.00.0911300722370.2872@localhost.localdomain> <20091130174638.GA9782@elte.hu> <alpine.LFD.2.00.0911302206370.24119@localhost.localdomain> <1259616429.26472.499.camel@laptop> <alpine.LFD.2.00.0911302300550.24119@localhost.localdomain> <alpine.LFD.2.00.0911301409560.2872@localhost.localdomain> <alpine.LFD.2.00.0911302328350.24119@localhost.localdomain> <alpine.LFD.2.00.0911301443110.2872@localhost.localdomain> <alpine.LFD.2.00.0912011608070.24119@localhost.localdomain>
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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.