From 754f8cb72b42a3a6100d2bbb1cb885361a7310dd Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 1 Jul 2016 16:34:29 -0400 Subject: [PATCH] ovl: do not require mounter to have MAY_WRITE on lower Now we have two levels of checks in ovl_permission(). overlay inode is checked with the creds of task while underlying inode is checked with the creds of mounter. Looks like mounter does not have to have WRITE access to files on lower/. So remove the MAY_WRITE from access mask for checks on underlying lower inode. This means task should still have the MAY_WRITE permission on lower inode and mounter is not required to have MAY_WRITE. It also solves the problem of read only NFS mounts being used as lower. If __inode_permission(lower_inode, MAY_WRITE) is called on read only NFS, it fails. By resetting MAY_WRITE, check succeeds and case of read only NFS shold work with overlay without having to specify any special mount options (default permission). Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/overlayfs/inode.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 5becbaf1cec7..8f7dd547cfb3 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -184,6 +184,8 @@ int ovl_permission(struct inode *inode, int mask) return err; old_cred = ovl_override_creds(inode->i_sb); + if (!is_upper) + mask &= ~(MAY_WRITE | MAY_APPEND); err = __inode_permission(realinode, mask); revert_creds(old_cred); -- 2.20.1