Commit fae19893 authored by Nicolai Stange's avatar Nicolai Stange Committed by Herbert Xu
Browse files

crypto: dh - split out deserialization code from crypto_dh_decode() 



A subsequent commit will introduce "dh" wrapping templates of the form
"ffdhe2048(dh)", "ffdhe3072(dh)" and so on in order to provide built-in
support for the well-known safe-prime ffdhe group parameters specified in
RFC 7919.

Those templates' ->set_secret() will wrap the inner "dh" implementation's
->set_secret() and set the ->p and ->g group parameters as appropriate on
the way inwards. More specifically,
- A ffdheXYZ(dh) user would call crypto_dh_encode() on a struct dh instance
  having ->p == ->g == NULL as well as ->p_size == ->g_size == 0 and pass
  the resulting buffer to the outer ->set_secret().
- This outer ->set_secret() would then decode the struct dh via
  crypto_dh_decode_key(), set ->p, ->g, ->p_size as well as ->g_size as
  appropriate for the group in question and encode the struct dh again
  before passing it further down to the inner "dh"'s ->set_secret().

The problem is that crypto_dh_decode_key() implements some basic checks
which would reject parameter sets with ->p_size == 0 and thus, the ffdheXYZ
templates' ->set_secret() cannot use it as-is for decoding the passed
buffer. As the inner "dh"'s ->set_secret() will eventually conduct said
checks on the final parameter set anyway, the outer ->set_secret() really
only needs the decoding functionality.

Split out the pure struct dh decoding part from crypto_dh_decode_key() into
the new __crypto_dh_decode_key().

__crypto_dh_decode_key() gets defined in crypto/dh_helper.c, but will have
to get called from crypto/dh.c and thus, its declaration must be somehow
made available to the latter. Strictly speaking, __crypto_dh_decode_key()
is internal to the dh_generic module, yet it would be a bit over the top
to introduce a new header like e.g. include/crypto/internal/dh.h
containing just a single prototype. Add the __crypto_dh_decode_key()
declaration to include/crypto/dh.h instead.

Provide a proper kernel-doc annotation, even though
__crypto_dh_decode_key() is purposedly not on the function list specified
in Documentation/crypto/api-kpp.rst.

Signed-off-by: default avatarNicolai Stange <nstange@suse.de>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 215bebc8

crypto/dh_helper.c

+19 −8
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ int crypto_dh_encode_key(char *buf, unsigned int len, const struct dh *params) 
}

EXPORT_SYMBOL_GPL(crypto_dh_encode_key);



int crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params)

int __crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params)

{

	const u8 *ptr = buf;

	struct kpp_secret secret;
@@ -81,6 +81,24 @@ int crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params) 
	if (secret.len != crypto_dh_key_len(params))

		return -EINVAL;



	/* Don't allocate memory. Set pointers to data within

	 * the given buffer

	 */

	params->key = (void *)ptr;

	params->p = (void *)(ptr + params->key_size);

	params->g = (void *)(ptr + params->key_size + params->p_size);



	return 0;

}



int crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params)

{

	int err;



	err = __crypto_dh_decode_key(buf, len, params);

	if (err)

		return err;



	/*

	 * Don't permit the buffer for 'key' or 'g' to be larger than 'p', since

	 * some drivers assume otherwise.
@@ -89,13 +107,6 @@ int crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params) 
	    params->g_size > params->p_size)

		return -EINVAL;



	/* Don't allocate memory. Set pointers to data within

	 * the given buffer

	 */

	params->key = (void *)ptr;

	params->p = (void *)(ptr + params->key_size);

	params->g = (void *)(ptr + params->key_size + params->p_size);



	/*

	 * Don't permit 'p' to be 0.  It's not a prime number, and it's subject

	 * to corner cases such as 'mod 0' being undefined or

include/crypto/dh.h

+16 −0
Original line number Diff line number Diff line
@@ -79,4 +79,20 @@ int crypto_dh_encode_key(char *buf, unsigned int len, const struct dh *params); 
 */

int crypto_dh_decode_key(const char *buf, unsigned int len, struct dh *params);



/**

 * __crypto_dh_decode_key() - decode a private key without parameter checks

 * @buf:	Buffer holding a packet key that should be decoded

 * @len:	Length of the packet private key buffer

 * @params:	Buffer allocated by the caller that is filled with the

 *		unpacked DH private key.

 *

 * Internal function providing the same services as the exported

 * crypto_dh_decode_key(), but without any of those basic parameter

 * checks conducted by the latter.

 *

 * Return:	-EINVAL if buffer has insufficient size, 0 on success

 */

int __crypto_dh_decode_key(const char *buf, unsigned int len,

			   struct dh *params);



#endif