linux-kernel - Re: [PATCH] sanitize task->comm to avoid leaking escape codes

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Message-ID: <20100623194145.GA19628@redhat.com>
Date:	Wed, 23 Jun 2010 21:41:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Neil Horman <nhorman@...driver.com>,
	Roland McGrath <roland@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sanitize task->comm to avoid leaking escape codes

On 06/23, Kees Cook wrote:
>
> @@ -956,7 +957,15 @@ void set_task_comm(struct task_struct *tsk, char *buf)
>  	 */
>  	memset(tsk->comm, 0, TASK_COMM_LEN);
>  	wmb();

Off-topic. I'd wish I could understand this barrier. Since the lockless
reader doesn't do rmb() I don't see how this can help. OTOH, I don't
understand why it is needed, we never change ->comm[TASK_COMM_LEN-1] == '0'.

> -	strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> +
> +	/* sanitize non-printable characters */
> +	for (i = 0; buf[i] && i < (sizeof(tsk->comm) - 1); i++) {
> +		if (!isprint(buf[i]))
> +			tsk->comm[i] = '?';
> +		else
> +			tsk->comm[i] = buf[i];
> +	}

Personally I think this makes sense.

> -extern char *get_task_comm(char *to, struct task_struct *tsk);
> +#define get_task_comm(buf, task) get_task_comm_size(buf, sizeof(buf), task)
> +extern char *get_task_comm_size(char *to, size_t len, struct task_struct *tsk);

Oh, but this means that get_task_comm(ptr, task) doesn't work?

Oleg.

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