linux-kernel - Re: [PATCH v1 1/9] certs: Fix blacklisted hexadecimal hash string check

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Message-ID: <113785.1607090759@warthog.procyon.org.uk>
Date:   Fri, 04 Dec 2020 14:05:59 +0000
From:   David Howells <dhowells@...hat.com>
To:     =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@...ikod.net>
Cc:     dhowells@...hat.com, David Woodhouse <dwmw2@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        James Morris <jmorris@...ei.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= 
        <mic@...ux.microsoft.com>, Mimi Zohar <zohar@...ux.ibm.com>,
        "Serge E . Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH v1 1/9] certs: Fix blacklisted hexadecimal hash string check

Mickaël Salaün <mic@...ikod.net> wrote:

> When looking for a blacklisted hash, bin2hex() is used to transform a
> binary hash to an ascii (lowercase) hexadecimal string.  This string is
> then search for in the description of the keys from the blacklist
> keyring.  When adding a key to the blacklist keyring,
> blacklist_vet_description() checks the hash prefix and the hexadecimal
> string, but not that this string is lowercase.  It is then valid to set
> hashes with uppercase hexadecimal, which will be silently ignored by the
> kernel.
> 
> Add an additional check to blacklist_vet_description() to check that
> hexadecimal strings are in lowercase.

I wonder if it would be a better idea to allow the keyring type to adjust the
description string - in this instance to change it to all lowercase.

David