Re: [RFC PATCH 1/3] lsm: cleanup the size counters in security_getselfattr()

From: Paul Moore <paul@paul-moore.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	"John Johansen" <john.johansen@canonical.com>,
	"Mickaël Salaün" <mic@digikod.net>
Subject: Re: [RFC PATCH 1/3] lsm: cleanup the size counters in security_getselfattr()
Date: Wed, 25 Oct 2023 18:06:52 -0400	[thread overview]
Message-ID: <CAHC9VhTXV+TmfmWy+ysZ8eoLhSVKC8ycnM-MBFL3UHyRbXPaEA@mail.gmail.com> (raw)
In-Reply-To: <5df43557-7261-47a1-9066-b7ba42145af0@schaufler-ca.com>

On Wed, Oct 25, 2023 at 11:19 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
> On 10/24/2023 6:43 PM, Paul Moore wrote:
> > On Tue, Oct 24, 2023 at 6:23 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
> >> On 10/24/2023 2:35 PM, Paul Moore wrote:
> >>> Zero out all of the size counters in the -E2BIG case (buffer too
> >>> small) to help make the current code a bit more robust in the face of
> >>> future code changes.
> >> I don't see how this change would have the described effect.
> >> What it looks like it would do is change the return from -E2BIG
> >> to 0, which would not have the desired result.
> > When @toobig is true, which it will be when one of the individual LSMs
> > return -E2BIG, the return value of security_getselfattr() is fixed to
> > -E2BIG (check the if-statements at the end of the function).  Setting
> > @rc to zero as in this patch simply preserves some sanity in the
> > @count variable as we are no longer subtracting the E2BIG errno from
> > the @count value.  Granted, in the @toobig case, @count doesn't do
> > anything meaningful, but I believe this does harden the code against
> > future changes.
> >
> > Look at the discussion between Mickaël and I in the v15 04/11 patch
> > for more background.
> >
> > https://lore.kernel.org/linux-security-module/20230912205658.3432-5-casey@schaufler-ca.com
>
> OK. My bad for not looking beyond the patch.

No problem, we all get caught out from time to time, thanks for the review/ACK.

-- 
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