( Please consider trimming the Cc list if discussing some aspect of this that doesn't concern everyone ) When an unprivileged process attempts to modify a file that has the setuid or setgid bits set, the VFS will attempt to clear these bits. The VFS will set the ATTR_KILL_SUID or ATTR_KILL_SGID bits in the ia_valid mask, and then call notify_change to clear these bits and set the mode accordingly. With a networked filesystem (NFS in particular but most likely others), the client machine may not have credentials that allow for the clearing of these bits. In some situations, this can lead to file corruption, or to an operation failing outright because the setattr fails. In this situation, we'd like to just leave the handling of this to the server and ignore these bits. The problem is that by the time nfs_setattr is called, the VFS has already reinterpreted the ATTR_KILL_* bits into a mode change. We can't fix this in the filesystems where this is a problem, as doing so would leave us having to second-guess what the VFS wants us to do. So we need to change it so that filesystems have more flexibility in how to interpret the ATTR_KILL_* bits. The first patch in the following patchset moves this logic into a helper function, and then only calls this helper function for inodes that do not have a setattr operation defined. The subsequent patches fix up individual filesystem setattr functions to call this helper function. The upshot of this is that with this change, filesystems that define a setattr inode operation are now responsible for handling the ATTR_KILL bits as well. They can trivially do so by calling the helper, but they must do so. Some of the follow-on patches may not be strictly necessary, but I decided that it was better to take the conservative approach and call the helper when I wasn't sure. I've tried to CC the maintainers for the individual filesystems as well where I could find them, please let me know if there are others who should be informed. Comments and suggestions appreciated... Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
