[PATCH v2 14/28] mbedtls/external: support decoding multiple signer's cert

[Raymond Mao]

Hi Ilias,

On Wed, 8 May 2024 at 10:35, Ilias Apalodimas <ilias.apalodimas at linaro.org>
wrote:

> Hi Raymond
>
> On Tue, 7 May 2024 at 20:57, Raymond Mao <raymond.mao at linaro.org> wrote:
> >
> > Support decoding multiple signer's cert in the signed data within
> > a PKCS7 message.
>
> For all similar external mbedTLS patches, try to explain which belong
> to mbedTLS must be sent upstream and which ones we need to carry
> internally. I don't expect us to have to carry anything in U-Boot
>
> I can add a reference link to the MbedTLS PR for the patches marked with
"mbedtls/external".
But for enabling the features, we still need to merge them before the next
git
subtree update when those patches are merged in a MbedTLS release.

Regards,
Raymond

Thanks
> /Ilias
>
> >
> > Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
> > ---
> > Changes in v2
> > - None.
> >
> >  lib/mbedtls/external/mbedtls/library/pkcs7.c | 75 ++++++++++++--------
> >  1 file changed, 47 insertions(+), 28 deletions(-)
> >
> > diff --git a/lib/mbedtls/external/mbedtls/library/pkcs7.c
> b/lib/mbedtls/external/mbedtls/library/pkcs7.c
> > index da73fb341d6..01105227d7a 100644
> > --- a/lib/mbedtls/external/mbedtls/library/pkcs7.c
> > +++ b/lib/mbedtls/external/mbedtls/library/pkcs7.c
> > @@ -61,6 +61,36 @@ static int pkcs7_get_next_content_len(unsigned char
> **p, unsigned char *end,
> >      return ret;
> >  }
> >
> > +/**
> > + * Get and decode one cert from a sequence.
> > + * Return 0 for success,
> > + * Return negative error code for failure.
> > + **/
> > +static int pkcs7_get_one_cert(unsigned char **p, unsigned char *end,
> > +                              mbedtls_x509_crt *certs)
> > +{
> > +    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
> > +    size_t len = 0;
> > +    unsigned char *start = *p;
> > +    unsigned char *end_cert;
> > +
> > +    ret = mbedtls_asn1_get_tag(p, end, &len, MBEDTLS_ASN1_CONSTRUCTED
> > +                               | MBEDTLS_ASN1_SEQUENCE);
> > +    if (ret != 0) {
> > +        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_CERT, ret);
> > +    }
> > +
> > +    end_cert = *p + len;
> > +
> > +    if ((ret = mbedtls_x509_crt_parse_der(certs, start, end_cert -
> start)) < 0) {
> > +        return MBEDTLS_ERR_PKCS7_INVALID_CERT;
> > +    }
> > +
> > +    *p = end_cert;
> > +
> > +    return 0;
> > +}
> > +
> >  /**
> >   * version Version
> >   * Version ::= INTEGER
> > @@ -178,11 +208,12 @@ static int pkcs7_get_certificates(unsigned char
> **p, unsigned char *end,
> >                                    mbedtls_x509_crt *certs)
> >  {
> >      int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
> > -    size_t len1 = 0;
> > -    size_t len2 = 0;
> > -    unsigned char *end_set, *end_cert, *start;
> > +    size_t len = 0;
> > +    unsigned char *end_set;
> > +    int num_of_certs = 0;
> >
> > -    ret = mbedtls_asn1_get_tag(p, end, &len1, MBEDTLS_ASN1_CONSTRUCTED
> > +    /* Get the set of certs */
> > +    ret = mbedtls_asn1_get_tag(p, end, &len, MBEDTLS_ASN1_CONSTRUCTED
> >                                 | MBEDTLS_ASN1_CONTEXT_SPECIFIC);
> >      if (ret == MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
> >          return 0;
> > @@ -190,38 +221,26 @@ static int pkcs7_get_certificates(unsigned char
> **p, unsigned char *end,
> >      if (ret != 0) {
> >          return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_FORMAT, ret);
> >      }
> > -    start = *p;
> > -    end_set = *p + len1;
> > +    end_set = *p + len;
> >
> > -    ret = mbedtls_asn1_get_tag(p, end_set, &len2,
> MBEDTLS_ASN1_CONSTRUCTED
> > -                               | MBEDTLS_ASN1_SEQUENCE);
> > +    ret = pkcs7_get_one_cert(p, end_set, certs);
> >      if (ret != 0) {
> > -        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_CERT, ret);
> > +        return ret;
> >      }
> >
> > -    end_cert = *p + len2;
> > +    num_of_certs++;
> >
> > -    /*
> > -     * This is to verify that there is only one signer certificate. It
> seems it is
> > -     * not easy to differentiate between the chain vs different
> signer's certificate.
> > -     * So, we support only the root certificate and the single signer.
> > -     * The behaviour would be improved with addition of multiple signer
> support.
> > -     */
> > -    if (end_cert != end_set) {
> > -        return MBEDTLS_ERR_PKCS7_FEATURE_UNAVAILABLE;
> > -    }
> > -
> > -    if ((ret = mbedtls_x509_crt_parse_der(certs, start, len1)) < 0) {
> > -        return MBEDTLS_ERR_PKCS7_INVALID_CERT;
> > +    while (*p != end_set) {
> > +        ret = pkcs7_get_one_cert(p, end_set, certs);
> > +        if (ret != 0) {
> > +            return ret;
> > +        }
> > +        num_of_certs++;
> >      }
> >
> > -    *p = end_cert;
> > +    *p = end_set;
> >
> > -    /*
> > -     * Since in this version we strictly support single certificate,
> and reaching
> > -     * here implies we have parsed successfully, we return 1.
> > -     */
> > -    return 1;
> > +    return num_of_certs;
> >  }
> >
> >  /**
> > --
> > 2.25.1
> >
>