Segmentation fault (core dumped) when running dnsdist client mode and dbpf:excludeRange

[rage4]

• Program: dnsdist
• Issue type: Bug report

Short description

dnsdist client mode crashes with "Segmentation fault (core dumped)" when using eBPF excludeRange

Environment

• Operating system: Ubuntu 16.04 LTS with HWE kernel
• Software version: dnsdist 1.6.0-alpha0.326.master.gd799ea222
• Software source: PowerDNS repository

Steps to reproduce

1. setup dnsdist
2. add the following lines to config, restart

bpf = newBPFFilter(1024, 1024, 1024)
setDefaultBPFFilter(bpf)
bpf:blockQName(newDNSName("."))

dbpf = newDynBPFFilter(bpf)
dbpf:excludeRange({ "88.198.139.2/32", "88.198.139.3/32" })
registerDynBPFFilter(dbpf)

function maintenance()
 addBPFFilterDynBlocks(exceedQRate(100, 1), dbpf, 120)
 dbpf:purgeExpired()
end

3. run dnsdist -c

Expected behaviour

correct access to dnsdist client console

Actual behaviour

Segmentation fault (core dumped)

Other information

[rage4]

side note - as I'm aware the issue was there also in 1.5.x

[rgacogne]

Right, that's because newDynBPFFilter(bpf) returns nullptr (nil) in client mode, and then calling excludeRange on that pointer triggers a null pointer dereference..
We have seen that for other objects already, we can either return a mockup object or check for nullptr in all BPFFilter methods.

[pieterlexis]

I'm wondering if it would make sense to have multiple configs with all options enabled and test the client mode in our CI as well

[rgacogne]

I'm wondering if it would make sense to have multiple configs with all options enabled and test the client mode in our CI as well

That would be very nice to have, yes.