Subject: Re: [PATCH net-next v2] net: core: enable SO_BINDTODEVICE for non-root users

From: Vincent Bernat <[email-masked]>
Date: Tue, 27 Oct 2020 08:17:41 +0100

❦ 23 octobre 2020 08:40 -06, David Ahern:

>> I am wondering if we should revert the patch for 5.10 while we can,
>> waiting for a better solution (and breaking people relying on the new
>> behavior in 5.9).
>> 
>> Then, I can propose a patch with a sysctl to avoid breaking existing
>> setups.
>> 
>
> I have not walked the details, but it seems like a security policy can
> be installed to get the previous behavior.

libtorrent is using SO_BINDTODEVICE for some reason (code is quite old,
so not git history). Previously, the call was unsuccesful and the error
was logged and ignored. Now, it succeeds and circumvent the routing
policy. Using Netfiler does not help as libtorrent won't act on dropped
packets as the socket is already configured on the wrong interface.
kprobe is unable to modify a syscall and seccomp cannot be applied
globally. LSM are usually distro specific. What kind of security policy
do you have in mind?

Thanks.
-- 
Don't over-comment.
            - The Elements of Programming Style (Kernighan & Plauger)