Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Pull overlayfs updates from Miklos Szeredi:
 "This contains several bug fixes and a new mount option
  'default_permissions' that allows read-only exported NFS
  filesystems to be used as lower layer"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: check dentry positiveness in ovl_cleanup_whiteouts()
  ovl: setattr: check permissions before copy-up
  ovl: root: copy attr
  ovl: move super block magic number to magic.h
  ovl: use a minimal buffer in ovl_copy_xattr
  ovl: allow zero size xattr
  ovl: default permissions

1 files changed, 36 insertions, 0 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 964a60fa7afc..bf996e574f3d 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -42,6 +42,19 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 	int err;
 	struct dentry *upperdentry;
 
+	/*
+	 * Check for permissions before trying to copy-up.  This is redundant
+	 * since it will be rechecked later by ->setattr() on upper dentry.  But
+	 * without this, copy-up can be triggered by just about anybody.
+	 *
+	 * We don't initialize inode->size, which just means that
+	 * inode_newsize_ok() will always check against MAX_LFS_FILESIZE and not
+	 * check for a swapfile (which this won't be anyway).
+	 */
+	err = inode_change_ok(dentry->d_inode, attr);
+	if (err)
+		return err;
+
 	err = ovl_want_write(dentry);
 	if (err)
 		goto out;
@@ -95,6 +108,29 @@ int ovl_permission(struct inode *inode, int mask)
 
 	realdentry = ovl_entry_real(oe, &is_upper);
 
+	if (ovl_is_default_permissions(inode)) {
+		struct kstat stat;
+		struct path realpath = { .dentry = realdentry };
+
+		if (mask & MAY_NOT_BLOCK)
+			return -ECHILD;
+
+		realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper);
+
+		err = vfs_getattr(&realpath, &stat);
+		if (err)
+			return err;
+
+		if ((stat.mode ^ inode->i_mode) & S_IFMT)
+			return -ESTALE;
+
+		inode->i_mode = stat.mode;
+		inode->i_uid = stat.uid;
+		inode->i_gid = stat.gid;
+
+		return generic_permission(inode, mask);
+	}
+
 	/* Careful in RCU walk mode */
 	realinode = ACCESS_ONCE(realdentry->d_inode);
 	if (!realinode) {