Hello, Few months ago I discussed with Steve that Linux SMB client has some problems during removal of directory which has read-only attribute set. I was looking what exactly the read-only windows attribute means, how it is interpreted by Linux and in my opinion it is wrongly used in Linux at all. Windows filesystems NTFS and ReFS, and also exported over SMB supports two ways how to present some file or directory as read-only. First option is by setting ACL permissions (for particular or all users) to GENERIC_READ-only. Second option is by setting the read-only attribute. Second option is available also for (ex)FAT filesystems (first option via ACL is not possible on (ex)FAT as it does not have ACLs). First option (ACL) is basically same as clearing all "w" bits in mode and ACL (if present) on Linux. It enforces security permission behavior. Note that if the parent directory grants for user delete child permission then the file can be deleted. This behavior is same for Linux and Windows (on Windows there is separate ACL for delete child, on Linux it is part of directory's write permission). Second option (Windows read-only attribute) means that the file/dir cannot be opened in write mode, its metadata attribute cannot be changed and the file/dir cannot be deleted at all. But anybody who has WRITE_ATTRIBUTES ACL permission can clear this attribute and do whatever wants. Linux filesystems has similar thing to Windows read-only attribute (FILE_ATTRIBUTE_READONLY). It is "immutable" bit (FS_IMMUTABLE_FL), which can be set by the "chattr" tool. Seems that the only difference between Windows read-only and Linux immutable is that on Linux only process with CAP_LINUX_IMMUTABLE can set or clear this bit. On Windows it can be anybody who has write ACL. Now I'm thinking, how should be Windows read-only bit interpreted by Linux filesystems drivers (FAT, exFAT, NTFS, SMB)? I see few options: 0) Simply ignored. Disadvantage is that over network fs, user would not be able to do modify or delete such file, even as root. 1) Smartly ignored. Meaning that for local fs, it is ignored and for network fs it has to be cleared before any write/modify/delete operation. 2) Translated to Linux mode/ACL. So the user has some ability to see it or change it via chmod. Disadvantage is that it mix ACL/mode. 3) Translated to Linux FS_IMMUTABLE_FL. So the user can use lsattr / chattr to see or change it. Disadvantage is that this bit can be changed only by root or by CAP_LINUX_IMMUTABLE process. 4) Exported via some new xattr. User can see or change it. But for example recursive removal via rm -rf would be failing as rm would not know about this special new xattr. In any case, in my opinion, all Linux fs drivers for these filesystems (FAT, exFAT, NTFS, SMB, are there some others?) should handle this windows read-only bit in the same way. What do you think, what should be the best option? I have another idea. What about introducing a new FS_IMMUTABLE_USER_FL bit which have same behavior as FS_IMMUTABLE_FL, just it would be possible to set it for any user who has granted "write" permission? Instead of requiring CAP_LINUX_IMMUTABLE. I see a nice usecase that even ordinary user could be able to mark file as protected against removal or modification (for example some backup data). Pali
