linux-kernel - Re: [PATCH 3/9] VFS: Introduce a mount context

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: <24143.1493893342@warthog.procyon.org.uk>
Date:   Thu, 04 May 2017 11:22:22 +0100
From:   David Howells <dhowells@...hat.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, mszeredi@...hat.com
Subject: Re: [PATCH 3/9] VFS: Introduce a mount context

Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> > +	if (fs_type->fsopen && fs_type->mc_size < sizeof(*mc))
> > +		BUG();
> 
> So ->mc_size can be 0 (i.e. not explicitly initialized) if fs_type does
> not have ->fsopen. OK.

I need to be able to handle filesystems that don't support this yet.  Once all
filesystems support this, I would be able to take away the max_t() thing.

> > +	if (!src->ops->dup)
> > +		return ERR_PTR(-ENOTSUPP);
> > +
> > +	mc = kmemdup(src, src->fs_type->mc_size, GFP_KERNEL);
> 
> So this assumes that vfs_dup_mount_context is only used if ->mc_size is
> explicitly initialized. A max_t here as well probably wouldn't hurt.

If you don't provide an ->fsopen() op, you can't set src->ops, you don't see a
mount context and you can't call this function.  If you did supply an
->fsopen() op, the BUG() would've got you if you didn't set ->mc_size.

> > +	unsigned short mc_size;		/* Size of mount context to allocate */
> 
> Any particular reason to use a short? The struct doesn't pack any better.

But it leaves a hole someone else can use.  I try not to use fields larger
than I need to.

David