linux-kernel - Re: [patch 1/3] NFS: fix potential NULL pointer dereference

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Date:	Wed, 16 Apr 2008 16:40:28 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	bfields@...ldses.org, neilb@...e.de, ibm-acpi@....eng.br,
	len.brown@...el.com, kkeil@...e.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] NFS: fix potential NULL pointer dereference

On Thu, 2008-04-17 at 00:19 +0400, Cyrill Gorcunov wrote:
> Trond, I've just pointed the problem and its solution (which is seems
> to be a bit ugly, according to the rest nfs coding principle). So if
> you prefer to have such a check in 'walk_path' function - just say me
> that. You choose :) Thanks for comments

> > So? The defensive coding principle is that you perform validity checks
> > when the pointer is created. Otherwise, we could equally well have added
> > the NULL deref check to nfs4_path_walk()...

No, your fix was correct, it was just incomplete.

The point I was making above was that defensive programming means that
_all_ these validity/NULL pointer checks should really be done in
nfs4_validate_mount_data and nfs_validate_mount_data. We shouldn't rely
on checks in other parts of the code.

In fact, as an example: it looks to me as if the lack of a
nfs_server.hostname, leads to a lack of nfs_client->cl_hostname, which
will eventually cause an Oops if you 'cat /proc/fs/nfsfs/servers', or if
you hit the printk in nfs_update_inode(), or various other dprintk()s.

Trond

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