linux-kernel - Re: [PATCH v3 02/10] certs: Fix blacklisted hexadecimal hash string check

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Date:   Wed, 20 Jan 2021 05:43:52 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     David Howells <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>,
        Mickaël Salaün <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,
        Ben Boeckel <mathstuf@...il.com>
Subject: Re: [PATCH v3 02/10] certs: Fix blacklisted hexadecimal hash string
 check

On Thu, Jan 14, 2021 at 04:19:01PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
> 
> 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.
> 
> Cc: David Woodhouse <dwmw2@...radead.org>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Reviewed-by: Ben Boeckel <mathstuf@...il.com>
> ---
> 
> Changes since v2:
> * Cherry-pick v1 patch from
>   https://lore.kernel.org/lkml/2659836.1607940186@warthog.procyon.org.uk/
>   to rebase on v5.11-rc3.
> * Rearrange Cc order.
> ---
>  certs/blacklist.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/certs/blacklist.c b/certs/blacklist.c
> index 2719fb2fbc1c..a888b934a1cd 100644
> --- a/certs/blacklist.c
> +++ b/certs/blacklist.c
> @@ -37,7 +37,7 @@ static int blacklist_vet_description(const char *desc)
>  found_colon:
>  	desc++;
>  	for (; *desc; desc++) {
> -		if (!isxdigit(*desc))
> +		if (!isxdigit(*desc) || isupper(*desc))
>  			return -EINVAL;
>  		n++;
>  	}
> -- 
> 2.30.0
> 

Shouldn't this rather convert the upper case to lower case? I don't like
the ABI break that this causes.

/Jarkko