[Bug 1291369] [NEW] dnsmasq can't send OFFERS missing capabilities but doesn't check

[fish]

Public bug reported:

Hi,

I'm running dnsmasq in a (docker) container. If I tried to start dnsmasq
without arguments and it failed with:

    dnsmasq: setting capabilities failed: Operation not permitted

Guess this is expected because the container has limited privileges. The
odd thing is, if I start it with --no-daemon it starts just fine, it
receives the DISCOVERs and says it's sending the OFFERS. The log shows:

dnsmasq-dhcp: DHCPDISCOVER(eth1) a4:ba:db:0a:3f:ef 
dnsmasq-dhcp: DHCPOFFER(eth1) 192.168.101.183 a4:ba:db:0a:3f:ef 

But according to tcpdump it's trying to send this as unicast which isn't
possible (I only see arp requests to resolve 192.168.101.183).  This is
a strace when answering the request:
https://gist.github.com/discordianfish/687f4cb5756c9cf3d841

No idea whether this is just a obscure bug or dnsmasq trying to be
smart.  So guess in the end it needs just better error handling/checks
for capabilities.

** Affects: dnsmasq (Ubuntu)
     Importance: Undecided
         Status: New

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Title:
  dnsmasq can't send OFFERS missing capabilities but doesn't check

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