From: Taehee Yoo <[email protected]>
Date: Wed, 12 Dec 2018 10:19:26 +0900
> When bpfilter error occurred bpfilter_umh will be stopped via __stop_umh().
> The bpfilter_umh() couldn't start again because there is no restart
> routine.
>
> The section of bpfilter_umh_{start/end} is no longer .init.rodata
> because these area should be reused in the restart routine. hence
> the section name is changed to .bpfilter_umh.
>
> Test commands:
> $ iptables -vnL
> $ kill -9 <pid of bpfilter_umh>
> $ iptables -vnL
> [ 480.045136] bpfilter: write fail -32
>
> $ iptables -vnL
> iptables v1.8.1 (legacy): can't initialize iptables table `filter': No
> child processes
> Perhaps iptables or your kernel needs to be upgraded.
>
> Then, iptables command is always failed.
>
> Fixes: d2ba09c17a06 ("net: add skeleton of bpfilter kernel module")
> Signed-off-by: Taehee Yoo <[email protected]>
Thank you for this fix, but I am unsure if this is a complete solution.
First of all, you can only kill the bpfilter_umh as root right?
It is a big problem to allow the userspace to kill the umh program
because that will result in the pipes being leaked. Normally the
kernel takes down bpfilter_umh and calls fput() on the pipe file
descriptors via shutdown_umh().
In the kill -9 example above, that does not happen and that is why
we get the fd leak.
In this situation it will not reset info->pid to zero, and it also
will leave bpfilter_process_socktop non-NULL.
Therefore, it seems like the kernel has to perform these cleanup
actions if the bpfilter_umh process dies (from kill -9, or just
crashing). And I think if you manage that properly it will fix this
bug too.
