linux-kernel - Re: [PATCH v3] crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate

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Message-ID: <aPkLRkgrfBXpFvkt@wunner.de>
Date: Wed, 22 Oct 2025 18:50:14 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: David Howells <dhowells@...hat.com>,
	Ignat Korchagin <ignat@...udflare.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Vivek Goyal <vgoyal@...hat.com>, keyrings@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] crypto: asymmetric_keys - prevent overflow in
 asymmetric_key_generate_id

On Wed, Oct 22, 2025 at 02:23:02PM +0200, Thorsten Blum wrote:
> On 13. Oct 2025, at 17:39, Lukas Wunner wrote:
> > On Mon, Oct 13, 2025 at 01:40:10PM +0200, Thorsten Blum wrote:
> >> Use check_add_overflow() to guard against potential integer overflows
> >> when adding the binary blob lengths and the size of an asymmetric_key_id
> >> structure and return ERR_PTR(-EOVERFLOW) accordingly. This prevents a
> >> possible buffer overflow when copying data from potentially malicious
> >> X.509 certificate fields that can be arbitrarily large, such as ASN.1
> >> INTEGER serial numbers, issuer names, etc.
> >> 
> >> Fixes: 7901c1a8effb ("KEYS: Implement binary asymmetric key ID handling")
> >> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> 
> I removed stable@ after your feedback to v2, but shouldn't v3 be applied
> to stable as well?

The Fixes tag you included implicitly serves as a stable tag.
It's usually sufficient reason for stable maintainers to select
the patch for backporting to stable kernels.

I'm always a bit cautious with stable designations because
if the patch turns out to be buggy, we broke the stable kernels as well,
which is bad and embarrassing.

In this particular case, the patch is fine but the bug doesn't look
easy to trigger.  One would have to craft an extremely large certificate.
Possible, but not very common.  Hence it doesn't seem super important
to get this fixed in stable kernels and for this reason I wouldn't have
included a Fixes tag if this was my patch.

Thanks,

Lukas