nfsd4: fix crash on writing v4_end_grace before nfsd startup

J. Bruce Fields · J. Bruce Fields · commit 62a063b8e7d1 · 2018-11-28T18:36:02.000-05:00
Anatoly Trosinenko reports that this: 1) Checkout fresh master Linux branch (tested with commit e195ca6) 2) Copy x84_64-config-4.14 to .config, then enable NFS server v4 and build 3) From `kvm-xfstests shell`: results in NULL dereference in locks_end_grace. Check that nfsd has been started before trying to end the grace period. Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
@@ -1126,6 +1126,8 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
 		case 'Y':
 		case 'y':
 		case '1':
+			if (nn->nfsd_serv)
+				return -EBUSY;
 			nfsd4_end_grace(nn);
 			break;
 		default:
