linux-hardening - Re: [PATCH] apparmor: aa_buffer: Convert 1-element array to flexible array

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Message-ID: <202305111453.082DC179@keescook>
Date:   Thu, 11 May 2023 14:55:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     John Johansen <john.johansen@...onical.com>
Cc:     "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, apparmor@...ts.ubuntu.com,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] apparmor: aa_buffer: Convert 1-element array to flexible
 array

On Thu, May 11, 2023 at 02:48:29PM -0700, John Johansen wrote:
> On 5/11/23 14:34, Kees Cook wrote:
> > In the ongoing effort to convert all fake flexible arrays to proper
> > flexible arrays, replace aa_buffer's 1-element "buffer" member with a
> > flexible array.
> > 
> > Cc: John Johansen <john.johansen@...onical.com>
> > Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
> > Cc: Paul Moore <paul@...l-moore.com>
> > Cc: James Morris <jmorris@...ei.org>
> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
> > Cc: apparmor@...ts.ubuntu.com
> > Cc: linux-security-module@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Acked-by: John Johansen <john.johansen@...onical.com>
> 
> I have pulled this into my tree.

Thanks!

> 
> > ---
> > One thing I notice here is that it may be rare for "buffer" to ever change
> > for a given kernel. Could this just be made PATH_MAX * 2 directly and
> > remove the module parameter, etc, etc?
> 
> possibly. Currently the only use case I know of is for some stress testing
> where we drop the buffer size down really small to try and break things.
> This isn't part of the regular regression runs and could be handle with a
> config/compile time to a buffer size constant.

Okay, cool. I figured the conversion to fixed-size is sort of nice, but
it probably won't be of much use as-is since it's the buffer, not the
aa_buffer, is passed around. The compiler would still not have any idea
what the bounds are. :)

-- 
Kees Cook