Commit 72f9a07b authored Dec 08, 2017 by Eric Biggers Committed by David Howells Dec 08, 2017

KEYS: be careful with error codes in public_key_verify_signature()



In public_key_verify_signature(), if akcipher_request_alloc() fails, we
return -ENOMEM.  But that error code was set 25 lines above, and by
accident someone could easily insert new code in between that assigns to
'ret', which would introduce a signature verification bypass.  Make the
code clearer by moving the -ENOMEM down to where it is used.

Additionally, the callers of public_key_verify_signature() only consider
a negative return value to be an error.  This means that if any positive
return value is accidentally introduced deeper in the call stack (e.g.
'return EBADMSG' instead of 'return -EBADMSG' somewhere in RSA),
signature verification will be bypassed.  Make things more robust by
having public_key_verify_signature() warn about positive errors and
translate them into -EINVAL.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>

parent a80745a6

crypto/asymmetric_keys/public_key.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -73,7 +73,7 @@ int public_key_verify_signature(const struct public_key *pkey,
		char alg_name_buf[CRYPTO_MAX_ALG_NAME];
		void *output;
		unsigned int outlen;
		int ret = -ENOMEM;
		int ret;

		pr_devel("==>%s()\n", __func__);

		@@ -99,6 +99,7 @@ int public_key_verify_signature(const struct public_key *pkey,
		if (IS_ERR(tfm))
		return PTR_ERR(tfm);

		ret = -ENOMEM;
		req = akcipher_request_alloc(tfm, GFP_KERNEL);
		if (!req)
		goto error_free_tfm;
		@@ -127,7 +128,7 @@ int public_key_verify_signature(const struct public_key *pkey,
		* signature and returns that to us.
		*/
		ret = crypto_wait_req(crypto_akcipher_verify(req), &cwait);
		if (ret < 0)
		if (ret)
		goto out_free_output;

		/* Do the actual verification step. */
		@@ -142,6 +143,8 @@ int public_key_verify_signature(const struct public_key *pkey,
		error_free_tfm:
		crypto_free_akcipher(tfm);
		pr_devel("<==%s() = %d\n", __func__, ret);
		if (WARN_ON_ONCE(ret > 0))
		ret = -EINVAL;
		return ret;
		}
		EXPORT_SYMBOL_GPL(public_key_verify_signature);