linux-hardening - Re: [PATCH] btrfs: sysfs: Handle NULL return values

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Date:   Mon, 6 Feb 2023 10:37:13 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] btrfs: sysfs: Handle NULL return values

On Sun, Feb 05, 2023 at 08:13:30AM +0100, Greg KH wrote:
> On Sat, Feb 04, 2023 at 10:35:10AM -0800, Kees Cook wrote:
> > Each of to_fs_info(), discard_to_fs_info(), and to_space_info() can
> > return NULL values.
> 
> The code says it could, but I really do not think that is possible at
> all, especially based on the fact that there have never been any crashes
> reported here.

I'm not sure that's a useful measure if we're trying to improve
robustness under memory corruption, but at least one of those helpers is
performing a type check, not just a simple container_of(), etc.

Regardless, yeah, if this can be done without NULL returns, sure, let's
do it. I just don't know this code well enough to say what's possible.
:)

-- 
Kees Cook