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 and CIFS in particular but likely others), the client machine or process may not have credentials that allow for setting the mode. In some situations, this can lead to file corruption, an operation failing outright because the setattr fails, or to races that lead to a mode change being reverted. 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 the setattr op 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 adds a new inode operation called "killattr" and has notify change call it if it's defined. The purpose of this inode op is to properly interpret the ATTR_KILL_SUID and ATTR_KILL_SGID bits. Filesystems that do not declare a killattr inode operation will keep the existing behavior, converting these bits into a mode change. The next two patches add a killattr inode op for NFS and CIFS which just clears the bits (to allow the server to handle them). The final patch updates the Documentation dir to describe the new killattr inode operation. This patchset should apply cleanly to 2.6.23-rc3-mm1. 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
