nfsd: fix auth_domain reference leak on nlm operations

Well, that one was fun to track down.... And how did it manage to lurk for nearly 10 years?

--b.

commit 38069804ed036adbf23aa94eafd5400c4f92fe6b

Author: J. Bruce Fields <[email protected]>
Date:   Thu Mar 24 22:51:14 2011 -0400

nfsd: fix auth_domain reference leak on nlm operations

This was noticed by users who performed more than 2^32 lock operations and hence made this counter overflow (eventually leading to use-after-free's). Setting rq_client to NULL here means that it won't later get auth_domain_put() when it should be.

Appears to have been introduced in 2.5.42 by "[PATCH] kNFSd: Move auth domain lookup into svcauth" which moved most of the rq_client handling to common svcauth code, but left behind this one line.

index 0c6d816..7c831a2 100644
@@ -38,7 +38,6 @@ nlm_fopen(struct svc_rqst *rqstp, struct nfs_fh *f, struct file **filp)
 	exp_readlock();
 	nfserr = nfsd_open(rqstp, &fh, S_IFREG, NFSD_MAY_LOCK, filp);
 	fh_put(&fh);
-	rqstp->rq_client = NULL;
 	exp_readunlock();
  	/* We return nlm error codes as nlm doesn't know
 	 * about nfsd, but nfsd does know about nlm..