Re: [PATCH 03/12] X.509: Move certificate length retrieval into new helper

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 28 Sep 2023 19:32:32 +0200
Lukas Wunner <lukas@wunner.de> wrote:

> The upcoming in-kernel SPDM library (Security Protocol and Data Model,
> https://www.dmtf.org/dsp/DSP0274) needs to retrieve the length from
> ASN.1 DER-encoded X.509 certificates.
> 
> Such code already exists in x509_load_certificate_list(), so move it
> into a new helper for reuse by SPDM.
> 
> No functional change intended.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>

Good find :)  I vaguely remember carrying a hack for this so
good to do something more general + save on the duplication.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>


> ---
>  crypto/asymmetric_keys/x509_loader.c | 38 +++++++++++++++++++---------
>  include/keys/asymmetric-type.h       |  2 ++
>  2 files changed, 28 insertions(+), 12 deletions(-)
> 
> diff --git a/crypto/asymmetric_keys/x509_loader.c b/crypto/asymmetric_keys/x509_loader.c
> index a41741326998..121460a0de46 100644
> --- a/crypto/asymmetric_keys/x509_loader.c
> +++ b/crypto/asymmetric_keys/x509_loader.c
> @@ -4,28 +4,42 @@
>  #include <linux/key.h>
>  #include <keys/asymmetric-type.h>
>  
> +int x509_get_certificate_length(const u8 *p, unsigned long buflen)
> +{
> +	int plen;
> +
> +	/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
> +	 * than 256 bytes in size.
> +	 */
> +	if (buflen < 4)
> +		return -EINVAL;
> +
> +	if (p[0] != 0x30 &&
> +	    p[1] != 0x82)
> +		return -EINVAL;
> +
> +	plen = (p[2] << 8) | p[3];
> +	plen += 4;
> +	if (plen > buflen)
> +		return -EINVAL;
> +
> +	return plen;
> +}
> +EXPORT_SYMBOL_GPL(x509_get_certificate_length);
> +
>  int x509_load_certificate_list(const u8 cert_list[],
>  			       const unsigned long list_size,
>  			       const struct key *keyring)
>  {
>  	key_ref_t key;
>  	const u8 *p, *end;
> -	size_t plen;
> +	int plen;
>  
>  	p = cert_list;
>  	end = p + list_size;
>  	while (p < end) {
> -		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
> -		 * than 256 bytes in size.
> -		 */
> -		if (end - p < 4)
> -			goto dodgy_cert;
> -		if (p[0] != 0x30 &&
> -		    p[1] != 0x82)
> -			goto dodgy_cert;
> -		plen = (p[2] << 8) | p[3];
> -		plen += 4;
> -		if (plen > end - p)
> +		plen = x509_get_certificate_length(p, end - p);
> +		if (plen < 0)
>  			goto dodgy_cert;
>  
>  		key = key_create_or_update(make_key_ref(keyring, 1),
> diff --git a/include/keys/asymmetric-type.h b/include/keys/asymmetric-type.h
> index 69a13e1e5b2e..6705cfde25b9 100644
> --- a/include/keys/asymmetric-type.h
> +++ b/include/keys/asymmetric-type.h
> @@ -84,6 +84,8 @@ extern struct key *find_asymmetric_key(struct key *keyring,
>  				       const struct asymmetric_key_id *id_2,
>  				       bool partial);
>  
> +int x509_get_certificate_length(const u8 *p, unsigned long buflen);
> +
>  int x509_load_certificate_list(const u8 cert_list[], const unsigned long list_size,
>  			       const struct key *keyring);
>