[PATCH] firmware_loader: load files from the mount namespace of init

[Topi Miettinen]

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Hi,

I have an experimental setup where almost every possible system service 
(even early startup ones) runs in separate namespace, using a dedicated, 
minimal file system. In process of minimizing the contents of the file 
systems with regards to modules and firmware files, I noticed that in my 
system, the firmware files are loaded from three different mount 
namespaces, those of systemd-udevd, init and systemd-networkd. The logic 
of the source namespace is not very clear, it seems to depend on the 
driver, but the namespace of the current process is used.

So, this patch tries to make things a bit clearer and changes the 
loading of firmware files only from the mount namespace of init. This 
may also improve security, though I think that using firmware files as 
attack vector could be too impractical anyway.

Later, it might make sense to make the mount namespace configurable, for 
example with a new file in
/proc/sys/kernel/firmware_config/. That would allow a dedicated file 
system only for firmware files and those need not be present anywhere 
else. This configurability would make more sense if made also for kernel 
modules and /sbin/modprobe. Modules are already loaded from init 
namespace (usermodehelper uses kthreadd namespace) except when directly 
loaded by systemd-udevd.

-Topi