ima: fix freeing ongoing ahash_request

integrity_kernel_read() can fail in which case we forward to call
ahash_request_free() on a currently running request. We have to wait
for its completion before we can free the request.

This was observed by interrupting a "find / -type f -xdev -print0 | xargs -0
cat 1>/dev/null" with ctrl-c on an IMA enabled filesystem.

Signed-off-by: Sascha Hauer <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

security/integrity/ima/ima_crypto.c

···
 		if (rc != rbuf_len) {
 			if (rc >= 0)
 				rc = -EINVAL;
+			/*
+			 * Forward current rc, do not overwrite with return value
+			 * from ahash_wait()
+			 */
+			ahash_wait(ahash_rc, &wait);
 			goto out3;
 		}