NFSD: fix use-after-free in __nfs42_ssc_open()

Problem caused by source's vfsmount being unmounted but remains
on the delayed unmount list. This happens when nfs42_ssc_open()
return errors.

Fixed by removing nfsd4_interssc_connect(), leave the vfsmount
for the laundromat to unmount when idle time expires.

We don't need to call nfs_do_sb_deactive when nfs42_ssc_open
return errors since the file was not opened so nfs_server->active
was not incremented. Same as in nfsd4_copy, if we fail to
launch nfsd4_do_async_copy thread then there's no need to
call nfs_do_sb_deactive
Reported-by: Xingyuan Mo <hdthky0@gmail.com>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Tested-by: Xingyuan Mo <hdthky0@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4proc.c

@@ -1461,13 +1461,6 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
 	return status;
 }
 
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-	nfs_do_sb_deactive(ss_mnt->mnt_sb);
-	mntput(ss_mnt);
-}
-
 /*
  * Verify COPY destination stateid.
  *
@@ -1570,11 +1563,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
 {
 }
 
-static void
-nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
-{
-}
-
 static struct file *nfs42_ssc_open(struct vfsmount *ss_mnt,
 				   struct nfs_fh *src_fh,
 				   nfs4_stateid *stateid)
@@ -1770,7 +1758,7 @@ static int nfsd4_do_async_copy(void *data)
 			default:
 				nfserr = nfserr_offload_denied;
 			}
-			nfsd4_interssc_disconnect(copy->ss_mnt);
+			/* ss_mnt will be unmounted by the laundromat */
 			goto do_callback;
 		}
 		nfserr = nfsd4_do_copy(copy, filp, copy->nf_dst->nf_file,
@@ -1851,8 +1839,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (async_copy)
 		cleanup_async_copy(async_copy);
 	status = nfserrno(-ENOMEM);
-	if (nfsd4_ssc_is_inter(copy))
-		nfsd4_interssc_disconnect(copy->ss_mnt);
+	/*
+	 * source's vfsmount of inter-copy will be unmounted
+	 * by the laundromat
+	 */
 	goto out;
 }