[PATCH v4 1/7] lib: crypto: add public_key_verify_signature()

[AKASHI Takahiro]

Heinrich,

On Sun, Jul 19, 2020 at 10:20:58AM +0200, Heinrich Schuchardt wrote:
> On 7/17/20 9:16 AM, AKASHI Takahiro wrote:
> > This function will be called from x509_check_for_self_signed() and
> > pkcs7_verify_one(), which will be imported from linux in a later patch.
> >
> > While it does exist in linux code and has a similar functionality of
> > rsa_verify(), it calls further linux-specific interfaces inside.
> > That could lead to more files being imported from linux.
> >
> > So simply re-implement it here instead of re-using the code.
> >
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> > ---
> >  include/crypto/public_key.h |  2 +-
> >  lib/crypto/public_key.c     | 70 ++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 70 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> > index 436a1ee1ee64..3ba90fcc3483 100644
> > --- a/include/crypto/public_key.h
> > +++ b/include/crypto/public_key.h
> > @@ -82,9 +82,9 @@ extern int decrypt_blob(struct kernel_pkey_params *, const void *, void *);
> >  extern int create_signature(struct kernel_pkey_params *, const void *, void *);
> >  extern int verify_signature(const struct key *,
> >  			    const struct public_key_signature *);
> > +#endif /* __UBOOT__ */
> >
> >  int public_key_verify_signature(const struct public_key *pkey,
> >  				const struct public_key_signature *sig);
> > -#endif /* !__UBOOT__ */
> >
> >  #endif /* _LINUX_PUBLIC_KEY_H */
> > diff --git a/lib/crypto/public_key.c b/lib/crypto/public_key.c
> > index e12ebbb3d0c5..71a0e0356beb 100644
> > --- a/lib/crypto/public_key.c
> > +++ b/lib/crypto/public_key.c
> > @@ -25,7 +25,10 @@
> >  #include <keys/asymmetric-subtype.h>
> >  #endif
> >  #include <crypto/public_key.h>
> > -#ifndef __UBOOT__
> > +#ifdef __UBOOT__
> > +#include <image.h>
> > +#include <u-boot/rsa.h>
> > +#else
> >  #include <crypto/akcipher.h>
> >  #endif
> 
> Shouldn't we describe in the header of the file that the code is taken
> (at least partially) from Linux' crypto/asymmetric_keys/public_key.c?
> 
> Please, also state the Linux version number.

Please take a look at the commit c4e961ecec99 ("lib: crypto: add public
key utility") as this file itself was imported in v2020-01. 

While I prefer to add such an information in a commit message,
we should have an explicit rule for inclusion from outer sources
for consistency over the tree if you want to see such an information
in a file.

> >
> > @@ -80,6 +83,71 @@ void public_key_signature_free(struct public_key_signature *sig)
> >  }
> >  EXPORT_SYMBOL_GPL(public_key_signature_free);
> >
> > +/**
> > + * public_key_verify_signature - Verify a signature using a public key.
> > + *
> > + * @pkey:	Public key
> > + * @sig:	Signature
> > + *
> > + * Verify a signature, @sig, using a RSA public key, @pkey.
> > + *
> > + * Return:	0 - verified, non-zero error code - otherwise
> > + */
> > +int public_key_verify_signature(const struct public_key *pkey,
> > +				const struct public_key_signature *sig)
> > +{
> > +	struct image_sign_info info;
> > +	struct image_region region;
> > +	int ret;
> > +
> > +	pr_devel("==>%s()\n", __func__);
> > +
> > +	if (!pkey || !sig)
> > +		return -EINVAL;
> > +
> > +	if (pkey->key_is_private)
> > +		return -EINVAL;
> > +
> > +	memset(&info, '\0', sizeof(info));
> > +	info.padding = image_get_padding_algo("pkcs-1.5");
> > +	/*
> > +	 * Note: image_get_[checksum|crypto]_algo takes a string
> > +	 * argument like "<checksum>,<crypto>"
> > +	 * TODO: support other hash algorithms
> > +	 */
> > +	if (strcmp(sig->pkey_algo, "rsa") || (sig->s_size * 8) != 2048) {
> > +		pr_warn("Encryption is not RSA2048: %s%d\n",
> > +			sig->pkey_algo, sig->s_size * 8);
> > +		return -ENOPKG;
> > +	}
> > +	if (!strcmp(sig->hash_algo, "sha1")) {
> > +		info.checksum = image_get_checksum_algo("sha1,rsa2048");
> > +		info.name = "sha1,rsa2048";
> > +	} else if (!strcmp(sig->hash_algo, "sha256")) {
> > +		info.checksum = image_get_checksum_algo("sha256,rsa2048");
> > +		info.name = "sha256,rsa2048";
> > +	} else {
> > +		pr_warn("unknown msg digest algo: %s\n", sig->hash_algo);
> > +		return -ENOPKG;
> > +	}
> > +	info.crypto = image_get_crypto_algo(info.name);
> > +	if (unlikely(IS_ERR(info.checksum) || IS_ERR(info.crypto)))
> > +		return -ENOPKG;
> 
> scripts/checkpatch.pl complains:
> 
> WARNING: nested (un)?likely() calls, IS_ERR already uses unlikely()
> internally
> #104: FILE: lib/crypto/public_key.c:134:
> +       if (unlikely(IS_ERR(info.checksum) || IS_ERR(info.crypto)))

Probably I missed it out when checking.

> I cannot find this unlikely in the Linux v5.8-rc4
> crypto/asymmetric_keys/public_key.c file. From where did you copy this code?

As I stated in the commit message, the whole code of this function
was written from the scratch rather than by re-using linux code.

-Takahiro Akashi


> Best regards
> 
> Heinrich
> 
> > +
> > +	info.key = pkey->key;
> > +	info.keylen = pkey->keylen;
> > +
> > +	region.data = sig->digest;
> > +	region.size = sig->digest_size;
> > +
> > +	if (rsa_verify_with_pkey(&info, sig->digest, sig->s, sig->s_size))
> > +		ret = -EKEYREJECTED;
> > +	else
> > +		ret = 0;
> > +
> > +	pr_devel("<==%s() = %d\n", __func__, ret);
> > +	return ret;
> > +}
> >  #else
> >  /*
> >   * Destroy a public key algorithm key.
> >
>