Re: [PATCHv5 iproute2] ip route: ignore ENOENT during save if RT_TABLE_MAIN is being dumped

[Roi Dayan <roid@nvidia.com>]

On 2021-07-11 1:59 PM, Roi Dayan wrote:
> 
> 
> On 2021-07-07 5:50 PM, patchwork-bot+netdevbpf@kernel.org wrote:
>> Hello:
>>
>> This patch was applied to iproute2/iproute2.git (refs/heads/main):
>>
>> On Wed,  7 Jul 2021 15:22:01 +0300 you wrote:
>>> We started to use in-kernel filtering feature which allows to get only
>>> needed tables (see iproute_dump_filter()). From the kernel side it's
>>> implemented in net/ipv4/fib_frontend.c (inet_dump_fib), 
>>> net/ipv6/ip6_fib.c
>>> (inet6_dump_fib). The problem here is that behaviour of "ip route save"
>>> was changed after
>>> c7e6371bc ("ip route: Add protocol, table id and device to dump 
>>> request").
>>> If filters are used, then kernel returns ENOENT error if requested table
>>> is absent, but in newly created net namespace even RT_TABLE_MAIN table
>>> doesn't exist. It is really allocated, for instance, after issuing
>>> "ip l set lo up".
>>>
>>> [...]
>>
>> Here is the summary with links:
>>    - [PATCHv5,iproute2] ip route: ignore ENOENT during save if 
>> RT_TABLE_MAIN is being dumped
>>      
>> https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=459ce6e3d792 
>>
>>
>> You are awesome, thank you!
>> -- 
>> Deet-doot-dot, I am a bot.
>> https://korg.docs.kernel.org/patchwork/pwbot.html
>>
>>
> 
> 
> Hi,
> 
> I didn't get a chance to check but after this commit the utility ss
> is crashing from libnetlink.c
> 
> (gdb) bt
> #0  0x0000000000000000 in ?? ()
> #1  0x0000000000418980 in rtnl_dump_done (a=0x7fffffffdc00, h=0x449c80) 
> at libnetlink.c:734
> #2  rtnl_dump_filter_l (rth=rth@entry=0x7fffffffdcf0, 
> arg=arg@entry=0x7fffffffdc00) at libnetlink.c:893
> #3  0x00000000004197a2 in rtnl_dump_filter_nc 
> (rth=rth@entry=0x7fffffffdcf0, filter=filter@entry=0x40cdf0 
> <show_one_inet_sock>,
>      arg1=arg1@entry=0x7fffffffdca0, nc_flags=nc_flags@entry=0) at 
> libnetlink.c:957
> #4  0x0000000000406dc7 in inet_show_netlink (dump_fp=dump_fp@entry=0x0, 
> protocol=protocol@entry=255, f=0x42e900 <current_filter>) at ss.c:3638
> #5  0x0000000000404db3 in raw_show (f=0x42e900 <current_filter>) at 
> ss.c:3939
> 
> 
> if I revert this commit I can run the ss utility ok.
> 
> Thanks,
> Roi

I found for me ss crashed using a->errhndlr but it could be null
in rtnl_dump_done()

I see a second usage of a->errhndlr in rtnl_dump_error()