On Fri, Dec 07, 2018 at 08:49:16PM +0100, Alexander Lochmann wrote: > > _What_ SUID bit? We are talking about a write to block device, for fsck sake... > > > That's the way I understood Jan's explanation: > " > Thinking more about this I'm not sure if this is actually the right > solution. Because for example the write(2) can set S_NOSEC flag wrongly > when it would race with chmod adding SUID bit. So probably we rather need > to acquire i_rwsem in blkdev_write_iter() if file does not have S_NOSEC set > (we don't want to acquire it unconditionally as that would heavily impact > scalability of block device writes). IDGI. We are talking about a block device here. What business could file_remove_privs() have doing _anything_ to it? should_remove_suid() returns to return 0 for those; what case do you have in mind? Somebody setting security.capabilities on a block device inode? IMO the bug here is file_remove_privs() not buggering off immediately after having observed that we are dealing with a block device. It really has nothing useful to do.
