[Toybox] banging on ping

[Rob Landley]

On 07/17/2017 09:55 AM, enh wrote:
> On Mon, Jul 17, 2017 at 3:33 AM, Rob Landley <rob at landley.net> wrote:
>> Over the weekend I started looking at ping.c again thinking "this seems
>> really easy, why haven't I already done it". And I figured out why (I
>> wanted the code to autodetect ipv4 or ipv6 without you having to
>> specify, but you could go "ping -I lo 127.0.0.1" and it could see ::1 as
>> the first address of lo so you have to defer the decision of which type
>> to use while detecting, AND I still wanted -4 and -6 to work to force
>> the decision meaning it fails if source or dest can't do that, except
>> supplying source address is optional.)
>>
>> So I finally untangled all that crap, and then I started in on the next
>> thing I wantedit to do, use the "unprivileged ping sockets" stuff Linux
>> merged back in 2011:
>>
>>   https://lwn.net/Articles/422330/
>>
>> It's almost been 7 years, no need to support the old "needs root" stuff
>> if this should be ubiquitously deployed.
>>
>> Yes that description's wrong, there's no such thing as PROT_ICMP, they
>> mean IPPROTO_ICMP but good luck finding example code using that because
>> nobody uses it. Why does nobody use it? Because the API is stupidly
>> disabled for no apparent reason.
> 
> Android uses it all over the place. i even made it available to Java.
> 
> in particular, external/iputils' ping/ping6 uses it.

Did you patch the stupid out of the kernel, or does your init script
just "echo 0 65535 > /proc/sys/net/ipv4/ping_group_range"?

(Honestly, what's the point or creating a new API to do the same thing
without requiring root access, and then not even let ROOT use it by
default? I thought busybox was using this, but they yanked it back OUT
in 2014: https://git.busybox.net/busybox/commit/?id=f0058b1b1fe9
because of this nonsense.)

Right. The kernel patch to fix this is:

--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1712,12 +1712,8 @@ static __net_init int inet_init_net(struct net *net)
        net->ipv4.ip_local_ports.range[1] =  60999;
 
        seqlock_init(&net->ipv4.ping_group_range.lock);
-       /*
-        * Sane defaults - nobody may create ping sockets.
-        * Boot scripts should set this to distro-specific group.
-        */
-       net->ipv4.ping_group_range.range[0] = make_kgid(&init_user_ns, 1);
-       net->ipv4.ping_group_range.range[1] = make_kgid(&init_user_ns, 0);
+       net->ipv4.ping_group_range.range[0] = make_kgid(&init_user_ns, 0);
+       net->ipv4.ping_group_range.range[1] = make_kgid(&init_user_ns, 65535);
 
        /* Default values for sysctl-controlled parameters.
         * We set them here, in case sysctl is not compiled.

And I think I'll just put that patch in the toybox FAQ rather than
implementing two APIs to do the same darn thing. I've asked the kernel
guys what they were thinking (with my usual "I'm tracking down a bug
and I found PEOPLE at the end of it" diplomacy, ala
http://lkml.iu.edu/hypermail/linux/kernel/1707.2/01797.html ) and
I have no _idea_ what they'll say because this makes no sense to me.

Rob