linux-kernel - Re: [PATCH v3 105/110] namei: make unlazy_walk and terminate_walk handle nd->stack, add unlazy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150511234333.GA7232@ZenIV.linux.org.uk>
Date:	Tue, 12 May 2015 00:43:33 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 105/110] namei: make unlazy_walk and terminate_walk
 handle nd->stack, add unlazy_link

On Mon, May 11, 2015 at 07:08:05PM +0100, Al Viro wrote:
> +static bool legitimize_links(struct nameidata *nd)
> +{
> +	int i;
> +	for (i = 0; i < nd->depth; i++) {
> +		struct saved *last = nd->stack + i;
> +		if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
> +			drop_links(nd);
> +			nd->depth = i;

Broken, actually - it should be i + 1.  What happens is that we attempt to
grab references on nd->stack[...].link; if everything succeeds, we'd won.
If legitimizing nd->stack[i].link fails (e.g. ->d_seq has changed on us),
we
	* put_link everything in stack and clear nd->stack[...].cookie, making
sure that nobody will call ->put_link() on it later.
	* leave the things for terminate_walk() so that it would do
path_put() on everything we have grabbed and ignored everything we hadn't
even got around to.

But this failed legitimize_path() requires path_put() - we *can't* block
there (we wouldn't be able to do ->put_link() afterwards if we did), so
we just zero what we didn't grab and leave what we had for subsequent
path_put().  Which may be anything from "nothing" (mount_lock has been
touched) to "both vfsmount and dentry" (->d_seq mismatch).

So we need to set nd->depth to i + 1 here, not i.  As it is, we are risking
a vfsmount (and possibly dentry) leak.  Fixed and force-pushed...
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/