psa_export_key: Always set a valid data length
Make psa_export_key() always set a valid data_length when exporting,
even when there are errors. This makes the API easier to use for buggy
programs (like our test code).
Our test code previously used exported_length uninitialized when
checking to see that the buffer returned was all zero in import_export()
in the case where an error was returned from psa_export_key().
Initialize exported_length to an invalid length, and check that it gets
set properly by psa_export_key(), to avoid this using export_length
uninitialized. Note that the mem_is_zero() check is still valid when
psa_export_key() returns an error, e.g. where exported_length is 0, as
we want to check that nothing was written to the buffer on error.
Out test code also previous passed NULL for the data_length parameter of
psa_export_key() when it expected a failure (in key_policy_fail()).
However, data_length is not allowed to be NULL, especially now that we
write to data_length from psa_export_key() even when there are errors.
Update the test code to not pass in a NULL data_length.
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 2670e41..de2bf40 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -636,6 +636,12 @@
{
key_slot_t *slot;
+ /* Set the key to empty now, so that even when there are errors, we always
+ * set data_length to a value between 0 and data_size. On error, setting
+ * the key to empty is a good choice because an empty key representation is
+ * unlikely to be accepted anywhere. */
+ *data_length = 0;
+
if( key == 0 || key > PSA_KEY_SLOT_COUNT )
return( PSA_ERROR_EMPTY_SLOT );
slot = &global_data.key_slots[key];
