dlm: make find_rsb() fail gracefully when namelen is too large

We *can* get there from receive_request() and dlm_recover_master_copy()
with namelen too large if incoming request is invalid; BUG() from
DLM_ASSERT() in allocate_rsb() is a bit excessive reaction to that
and in case of dlm_recover_master_copy() we would actually oops before
that while calculating hash of up to 64Kb worth of data - with data
actually being 64 _bytes_ in kmalloc()'ed struct.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/lock.c

@@ -436,11 +436,15 @@ static int find_rsb(struct dlm_ls *ls, char *name, int namelen,
 {
 	struct dlm_rsb *r, *tmp;
 	uint32_t hash, bucket;
-	int error = 0;
+	int error = -EINVAL;
+
+	if (namelen > DLM_RESNAME_MAXLEN)
+		goto out;
 
 	if (dlm_no_directory(ls))
 		flags |= R_CREATE;
 
+	error = 0;
 	hash = jhash(name, namelen, 0);
 	bucket = hash & (ls->ls_rsbtbl_size - 1);