NLM: Defend against file_lock changes after vfs_test_lock()

Instead of trusting that struct file_lock returns completely unchanged
after vfs_test_lock() when there's no conflicting lock, stash away our
nlm_lockowner reference so we can properly release it for all cases.

This defends against another file_lock implementation overwriting fl_owner
when the return type is F_UNLCK.
Reported-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
Tested-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/lockd/svc4proc.c

@@ -87,6 +87,7 @@ __nlm4svc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 	struct nlm_args *argp = rqstp->rq_argp;
 	struct nlm_host	*host;
 	struct nlm_file	*file;
+	struct nlm_lockowner *test_owner;
 	__be32 rc = rpc_success;
 
 	dprintk("lockd: TEST4        called\n");
@@ -96,6 +97,7 @@ __nlm4svc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 	if ((resp->status = nlm4svc_retrieve_args(rqstp, argp, &host, &file)))
 		return resp->status == nlm_drop_reply ? rpc_drop_reply :rpc_success;
 
+	test_owner = argp->lock.fl.fl_owner;
 	/* Now check for conflicting locks */
 	resp->status = nlmsvc_testlock(rqstp, file, host, &argp->lock, &resp->lock, &resp->cookie);
 	if (resp->status == nlm_drop_reply)
@@ -103,7 +105,7 @@ __nlm4svc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 	else
 		dprintk("lockd: TEST4        status %d\n", ntohl(resp->status));
 
-	nlmsvc_release_lockowner(&argp->lock);
+	nlmsvc_put_lockowner(test_owner);
 	nlmsvc_release_host(host);
 	nlm_release_file(file);
 	return rc;

fs/lockd/svclock.c

@@ -340,7 +340,7 @@ nlmsvc_get_lockowner(struct nlm_lockowner *lockowner)
 	return lockowner;
 }
 
-static void nlmsvc_put_lockowner(struct nlm_lockowner *lockowner)
+void nlmsvc_put_lockowner(struct nlm_lockowner *lockowner)
 {
 	if (!refcount_dec_and_lock(&lockowner->count, &lockowner->host->h_lock))
 		return;
@@ -590,7 +590,6 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 	int			error;
 	int			mode;
 	__be32			ret;
-	struct nlm_lockowner	*test_owner;
 
 	dprintk("lockd: nlmsvc_testlock(%s/%ld, ty=%d, %Ld-%Ld)\n",
 				nlmsvc_file_inode(file)->i_sb->s_id,
@@ -604,9 +603,6 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 		goto out;
 	}
 
-	/* If there's a conflicting lock, remember to clean up the test lock */
-	test_owner = (struct nlm_lockowner *)lock->fl.fl_owner;
-
 	mode = lock_to_openmode(&lock->fl);
 	error = vfs_test_lock(file->f_file[mode], &lock->fl);
 	if (error) {
@@ -635,10 +631,6 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 	conflock->fl.fl_end = lock->fl.fl_end;
 	locks_release_private(&lock->fl);
 
-	/* Clean up the test lock */
-	lock->fl.fl_owner = NULL;
-	nlmsvc_put_lockowner(test_owner);
-
 	ret = nlm_lck_denied;
 out:
 	return ret;

fs/lockd/svcproc.c

@@ -116,6 +116,7 @@ __nlmsvc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 	struct nlm_args *argp = rqstp->rq_argp;
 	struct nlm_host	*host;
 	struct nlm_file	*file;
+	struct nlm_lockowner *test_owner;
 	__be32 rc = rpc_success;
 
 	dprintk("lockd: TEST          called\n");
@@ -125,6 +126,8 @@ __nlmsvc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 	if ((resp->status = nlmsvc_retrieve_args(rqstp, argp, &host, &file)))
 		return resp->status == nlm_drop_reply ? rpc_drop_reply :rpc_success;
 
+	test_owner = argp->lock.fl.fl_owner;
+
 	/* Now check for conflicting locks */
 	resp->status = cast_status(nlmsvc_testlock(rqstp, file, host, &argp->lock, &resp->lock, &resp->cookie));
 	if (resp->status == nlm_drop_reply)
@@ -133,7 +136,7 @@ __nlmsvc_proc_test(struct svc_rqst *rqstp, struct nlm_res *resp)
 		dprintk("lockd: TEST          status %d vers %d\n",
 			ntohl(resp->status), rqstp->rq_vers);
 
-	nlmsvc_release_lockowner(&argp->lock);
+	nlmsvc_put_lockowner(test_owner);
 	nlmsvc_release_host(host);
 	nlm_release_file(file);
 	return rc;

include/linux/lockd/lockd.h

@@ -292,6 +292,7 @@ void		  nlmsvc_locks_init_private(struct file_lock *, struct nlm_host *, pid_t);
 __be32		  nlm_lookup_file(struct svc_rqst *, struct nlm_file **,
 					struct nlm_lock *);
 void		  nlm_release_file(struct nlm_file *);
+void		  nlmsvc_put_lockowner(struct nlm_lockowner *);
 void		  nlmsvc_release_lockowner(struct nlm_lock *);
 void		  nlmsvc_mark_resources(struct net *);
 void		  nlmsvc_free_host_resources(struct nlm_host *);