linux-kernel - Re: [PATCH v2011.2] fs: symlink restrictions on sticky directories

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Date:	Thu, 15 Dec 2011 07:48:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...otime.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Rik van Riel <riel@...hat.com>,
	Federica Teodori <federica.teodori@...glemail.com>,
	Lucian Adrian Grijincu <lucian.grijincu@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2011.2] fs: symlink restrictions on sticky directories


* Kees Cook <keescook@...omium.org> wrote:

> +	/* Check parent directory mode and owner. */
> +	spin_lock(&dentry->d_lock);
> +	parent = dentry->d_parent->d_inode;
> +	if ((parent->i_mode & (S_ISVTX|S_IWOTH)) == (S_ISVTX|S_IWOTH) &&
> +	    parent->i_uid != inode->i_uid) {
> +		error = -EACCES;
> +	}
> +	spin_unlock(&dentry->d_lock);
> +
> +#ifdef CONFIG_AUDIT
> +	if (error) {
> +		struct audit_buffer *ab;
> +
> +		ab = audit_log_start(current->audit_context,
> +				     GFP_ATOMIC, AUDIT_AVC);
> +		audit_log_format(ab, "op=follow_link action=denied");
> +		audit_log_d_path(ab, "path=", &nameidata->path);
> +		audit_log_format(ab, " name=");
> +		audit_log_untrustedstring(ab, dentry->d_name.name);
> +		audit_log_format(ab, " dev=%s ino=%lu",
> +				 inode->i_sb->s_id,
> +				 inode->i_ino);
> +		audit_log_end(ab);
> +	}
> +#endif

Hm, is GFP_ATOMIC really necessary here? Why not GFP_KERNEL? 
This is in VFS process context, not in some atomic context that 
has to be careful about allocations, right?

Thanks,

	Ingo
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