On Tue, Jul 18, 2017 at 02:13:51PM +0800, Herbert Xu wrote: > On Fri, Jun 30, 2017 at 05:27:34PM +0200, Richard Weinberger wrote: > > Hi! > > > > David and I faced a deadlock with switch_root when fscrypt was in use. > > When /sbin/modprobe is encrypted using fscrypt and no other kernel component > > requested an AES cipher before, first access to an encrypted file will trigger the > > module_request() function, which will execute usermode helper /sbin/modprobe. > > Is /sbin/modprobe also encrypted the kernel will deadlock because executing > > it will again enter the module_request() path... > > > > As workaround we currently do something like "ls /new_root > /dev/null" in our > > initramfs to make request_module() happen before we change the root directory > > to /new_root. > > > > While this workaround is legit we think that this could be handled better. > > Is there a way to request these ciphers before first usage? Herbert? > > e.g. such that the filesystem can request them upon mount time. > > > > Btw: This happens even when AES modules are builtins. > > I think you're running into the problem because of templates, where > the first instantiation will always be preceded by a request_module. > > We should be able to fix this by doing two template probes instead > of one. So instead of the current order: > > 1. Look up registered algorithms. > 2. Request module. > 3. Find templates (may request module). > > We can do > > 1. Look up registered algorithms. > 2. Find templates without loading modules. > 3. Request module. > 4. Find templates (may request module). > While that should solve the problem, isn't it possible to actually have a module which supplies an algorithm like "xts(aes)"? In that case it wouldn't be desirable to instantiate the generic "xts" template. Eric
