nfsd: make V4ROOT exports read-only

I can't see any use for writeable V4ROOT exports.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/export.c

@@ -355,7 +355,7 @@ static struct svc_export *svc_export_update(struct svc_export *new,
 					    struct svc_export *old);
 static struct svc_export *svc_export_lookup(struct svc_export *);
 
-static int check_export(struct inode *inode, int flags, unsigned char *uuid)
+static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
 {
 
 	/*
@@ -367,6 +367,13 @@ static int check_export(struct inode *inode, int flags, unsigned char *uuid)
 	    !S_ISREG(inode->i_mode))
 		return -ENOTDIR;
 
+	/*
+	 * Mountd should never pass down a writeable V4ROOT export, but,
+	 * just to make sure:
+	 */
+	if (*flags & NFSEXP_V4ROOT)
+		*flags |= NFSEXP_READONLY;
+
 	/* There are two requirements on a filesystem to be exportable.
 	 * 1:  We must be able to identify the filesystem from a number.
 	 *       either a device number (so FS_REQUIRES_DEV needed)
@@ -375,7 +382,7 @@ static int check_export(struct inode *inode, int flags, unsigned char *uuid)
 	 *       This means that s_export_op must be set.
 	 */
 	if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) &&
-	    !(flags & NFSEXP_FSID) &&
+	    !(*flags & NFSEXP_FSID) &&
 	    uuid == NULL) {
 		dprintk("exp_export: export of non-dev fs without fsid\n");
 		return -EINVAL;
@@ -590,7 +597,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
 				goto out4;
 		}
 
-		err = check_export(exp.ex_path.dentry->d_inode, exp.ex_flags,
+		err = check_export(exp.ex_path.dentry->d_inode, &exp.ex_flags,
 				   exp.ex_uuid);
 		if (err)
 			goto out4;
@@ -1029,7 +1036,7 @@ exp_export(struct nfsctl_export *nxp)
 		goto finish;
 	}
 
-	err = check_export(path.dentry->d_inode, nxp->ex_flags, NULL);
+	err = check_export(path.dentry->d_inode, &nxp->ex_flags, NULL);
 	if (err) goto finish;
 
 	err = -ENOMEM;