KEYS: DH: validate __spare field

commit 4f9dabfa upstream.

Syscalls must validate that their reserved arguments are zero and return
EINVAL otherwise.  Otherwise, it will be impossible to actually use them
for anything in the future because existing programs may be passing
garbage in.  This is standard practice when adding new APIs.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

security/keys/compat_dh.c

@@ -33,6 +33,8 @@ long compat_keyctl_dh_compute(struct keyctl_dh_params __user *params,
 	kdfcopy.hashname = compat_ptr(compat_kdfcopy.hashname);
 	kdfcopy.otherinfo = compat_ptr(compat_kdfcopy.otherinfo);
 	kdfcopy.otherinfolen = compat_kdfcopy.otherinfolen;
+	memcpy(kdfcopy.__spare, compat_kdfcopy.__spare,
+	       sizeof(kdfcopy.__spare));
 
 	return __keyctl_dh_compute(params, buffer, buflen, &kdfcopy);
 }

security/keys/dh.c

@@ -266,6 +266,11 @@ long __keyctl_dh_compute(struct keyctl_dh_params __user *params,
 	if (kdfcopy) {
 		char *hashname;
 
+		if (memchr_inv(kdfcopy->__spare, 0, sizeof(kdfcopy->__spare))) {
+			ret = -EINVAL;
+			goto out1;
+		}
+
 		if (buflen > KEYCTL_KDF_MAX_OUTPUT_LEN ||
 		    kdfcopy->otherinfolen > KEYCTL_KDF_MAX_OI_LEN) {
 			ret = -EMSGSIZE;