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KEYS: be careful with error codes in public_key_verify_signature()

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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>
This commit is contained in:
Eric Biggers 2017-12-08 15:13:29 +00:00 committed by David Howells
parent a80745a6de
commit 72f9a07b6b
1 changed files with 5 additions and 2 deletions
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7
crypto/asymmetric_keys/public_key.c
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@ -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 @@ error_free_req:
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);