linux-kernel - Re: [PATCH 3/3] RFC: p9auth: add p9auth fs

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Message-ID: <20100428111749.GA27247@redhat.com>
Date:	Wed, 28 Apr 2010 13:17:49 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Ashwin Ganti <ashwin.ganti@...il.com>,
	David Howells <dhowells@...hat.com>, Greg KH <greg@...ah.com>,
	rsc@...ch.com, ericvh@...il.com,
	linux-security-module@...r.kernel.org,
	Ron Minnich <rminnich@...il.com>, jt.beard@...il.com,
	Andrew Morgan <morgan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Kyle Moffett <kyle@...fetthome.net>,
	Steve Grubb <sgrubb@...hat.com>
Subject: Re: [PATCH 3/3] RFC: p9auth: add p9auth fs

On 04/27, Serge E. Hallyn wrote:
>
> This introduces a Plan 9 style setuid capability filesystem.
> See Documentation/p9auth.txt for a description of how to use this.

Can't comment these changes due to the lack of knowledge, just
a couple of minor nits.

> +static ssize_t p9auth_use_write(struct file *file, const char __user *buffer,
> +			       size_t count, loff_t *ppos)
> +{
> +	ssize_t retval = -ENOMEM;
> +	char *user_buf;
> +
> +	if (mutex_lock_interruptible(&cap_mutex))
> +		return -EINTR;

EINTR doesn't look exactly right here, especially if TIF_SIGPENDING is
spurious. Probably ERESTARTNOINTR makes more sense. Or mutex_lock_killable().

> +	user_buf = kzalloc(count+1, GFP_KERNEL);

Probably this is OK, but it looks a bit strange we do no check that
count is not too large.

> +	if (copy_from_user(user_buf, buffer, count)) {
> +		retval = -EFAULT;
> +		goto out;
> +	}
> +
> +	retval = use_setuid_capability(user_buf);

It seems that use_setuid_capability() pathes assume that user_buf is
null terminated? Say, parse_user_capability() does kstrdup(user_buf).

Oleg.

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