nfsd: fix possible oops on re-insertion of rpcsec_gss modules

The handling of the re-registration case is wrong here; the "test" that was
returned from auth_domain_lookup will not be used again, so that reference
should be put.  And auth_domain_lookup never did anything with "new" in
this case, so we should just clean it up ourself.

Thanks to Akinobu Mita for bug report, analysis, and testing.

Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

net/sunrpc/auth_gss/svcauth_gss.c

@@ -769,11 +769,12 @@ svcauth_gss_register_pseudoflavor(u32 pseudoflavor, char * name)
 	new->h.flavour = &svcauthops_gss;
 	new->pseudoflavor = pseudoflavor;
 
+	stat = 0;
 	test = auth_domain_lookup(name, &new->h);
-	if (test != &new->h) { /* XXX Duplicate registration? */
-		auth_domain_put(&new->h);
-		/* dangling ref-count... */
-		goto out;
+	if (test != &new->h) { /* Duplicate registration */
+		auth_domain_put(test);
+		kfree(new->h.name);
+		goto out_free_dom;
 	}
 	return 0;