Re: [PATCH net] bpf, inode: disallow userns mounts

[David Miller <davem@davemloft.net>]

From: Daniel Borkmann <daniel@iogearbox.net>
Date: Sun, 22 May 2016 23:16:18 +0200

> Follow-up to commit e27f4a942a0e ("bpf: Use mount_nodev not mount_ns
> to mount the bpf filesystem"), which removes the FS_USERNS_MOUNT flag.
> 
> The original idea was to have a per mountns instance instead of a
> single global fs instance, but that didn't work out and we had to
> switch to mount_nodev() model. The intent of that middle ground was
> that we avoid users who don't play nice to create endless instances
> of bpf fs which are difficult to control and discover from an admin
> point of view, but at the same time it would have allowed us to be
> more flexible with regard to namespaces.
> 
> Therefore, since we now did the switch to mount_nodev() as a fix
> where individual instances are created, we also need to remove userns
> mount flag along with it to avoid running into mentioned situation.
> I don't expect any breakage at this early point in time with removing
> the flag and we can revisit this later should the requirement for
> this come up with future users. This and commit e27f4a942a0e have
> been split to facilitate tracking should any of them run into the
> unlikely case of causing a regression.
> 
> Fixes: b2197755b263 ("bpf: add support for persistent maps/progs")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Acked-by: Alexei Starovoitov <ast@kernel.org>

Applied and queued up for -stable, thanks.