Re: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 bpf: prevent out of bounds speculation on pointer arithmetic

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 11, 2019 at 07:13:14PM +0800, Jason Yan wrote:
> 
> 
> On 2019/3/11 17:41, Daniel Borkmann wrote:
> > Hi Jason,
> > 
> > On 03/11/2019 10:18 AM, Jason Yan wrote:
> > > Hi, Daniel & Greg
> > > 
> > > This patch (979d63d50c0c bpf: prevent out of bounds speculation on pointer arithmetic) was assigned a CVE (CVE-2019-7308) with a high score:
> > > 
> > > CVSS v3.0 Severity and Metrics:
> > > Base Score: 9.8 CRITICAL
> > > 
> > > And this patch is not in stable-4.4, would you please backport this patch to 4.4?
> > 
> > We don't handle kernels as old as 4.4, so someone else would need to
> > do the backporting e.g. from your side. The series has been backported
> > to the last two most-recent stable kernels at that time (we usually
> > follow netdev practice here), and there have been asks about 4.14 as
> > well; I've been looking into backporting for the latter last two weeks
> > on and off, but there are conflicts all over the place in fragile core
> > areas where I didn't have enough free cycles to complete it yet. For
> > old kernels, you're probably better off doing something like this in
> > your tree instead of the huge complexity with a backport:
> > 
> 
> Thanks for you kindly reply.
> 
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index bc34cf9..2cea2de 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -47,7 +47,7 @@ static DEFINE_SPINLOCK(prog_idr_lock);
> >   static DEFINE_IDR(map_idr);
> >   static DEFINE_SPINLOCK(map_idr_lock);
> > 
> > -int sysctl_unprivileged_bpf_disabled __read_mostly;
> > +int sysctl_unprivileged_bpf_disabled __read_mostly = 1;
> > 
> 
> Greg, is it possible to get this kind of mitigation into 4.4?

Why are you using a 4.4 kernel with untrusted userspace?  The only
reason to use 4.4.y at this point in time is if you have a huge SoC tree
patchset that is not upstream.  If you are using x86, you should be
using 4.14.y or newer right now.

That being said, no, I am not going to change the default here, that
could break people's working setups.  I would recommend you just setting
this value in your initrd/setup scripts if you want it, that's why it is
a sysctl :)

thanks,

greg k-h