Re: net/ipv6: GPF in rt6_ifdown

On Wed, Jun 21, 2017 at 1:08 PM, Cong Wang [off-list ref] wrote:

On Wed, Jun 21, 2017 at 10:53 AM, Andrey Konovalov
[off-list ref] wrote:

quoted

On Wed, Jun 21, 2017 at 3:09 PM, Andrey Konovalov [off-list ref] wrote:

quoted

On Wed, Jun 21, 2017 at 2:08 PM, Andrey Konovalov [off-list ref] wrote:

quoted

Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

On commit 9705596d08ac87c18aee32cc97f2783b7d14624e (4.12-rc6+).

It might be related to:
https://groups.google.com/forum/#!topic/syzkaller/ZJaqAiFLe3k

I only have a reproducer in the form of a syzkaller program, attached
together with my .config.

I now have a C reproducer as well, attached.

And here's a much simpler reproducer.

Thanks a lot for your reproducer!

I added a few printk's, and find that we somehow have rt->rt6i_idev set
to NULL but still keep it in the uncached list. ip6_dst_destroy() unlinks
it before NULL'ing, so it should not be that case.

Heck... The loopback_dev->ip6_ptr is set to NULL because of
its mtu is set to smaller than IPV6_MIN_MTU, this is why we
have rt->rt6i_idev NULL after a rt6_uncached_list_flush_dev()...

I am thinking about a right fix.