[systemd-devel] [RFC][PATCH 1/2] resolve: resolved-manager: Avoid null dereference

[Tom Gundersen]

On Wed, Oct 22, 2014 at 10:39 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Wed, 22.10.14 22:12, Tom Gundersen (teg at jklm.no) wrote:
>
>> On Wed, Oct 22, 2014 at 12:19 PM, Lennart Poettering
>> <lennart at poettering.net> wrote:
>> > On Sat, 13.09.14 20:40, Tom Gundersen (teg at jklm.no) wrote:
>> >
>> >> Yeah, this could happen. It so happens that the loopback link will
>> >> always have ifindex 1, so I guess we could just fall back to checking
>> >> for that if we don't have the real flags.
>> >
>> > Is that true even in network namespaces? Is this really exported API?
>> > I really don't want to rely on behaviour here that is not considered
>> > official API of Linux.
>> >
>> > If it is safe API of Linux, then we really should drop
>> > manager_ifindex_is_loopback() entirely, and just always compare the
>> > ifindex.
>> >
>> > Anyone has some pointers where this is made API?
>>
>> We may want to ask the kernel guys to export LOOPBACK_IFINDEX, as it
>> is not at the moment. However, I think relying on it is fine even
>> without that as the kernel will BUG_ON if "lo" does not have ifindex
>> 1[0], and no other netdev can have ifindex 1[1]:
>>
>>         /* The loopback device is special if any other network devices
>>          * is present in a network namespace the loopback device must
>>          * be present.
>
> BTW, I changed resolved now to only use LOOPBACK_IFINDEX when
> identifying loopback devices, and dropped the code that checks for
> IFF_LOOPBACK. That should simplify things a bit.
>
> I also documented the situation around LOOPBACK_IFINDEX in the
> comments.


Thanks!

-t