dhcpcd-discuss

On 12/11/2020 22:58, Matthew Clarkson wrote:
> Hi Roy,
>
> We are running on an ARM32 with glibc 2.3.0. The distro is custom built using the Linux 4.9 kernel (with patches from our processor vendor) and built/configured using the Yocto project.
>
> I compiled with SECCOMP_FILTER_DEBUG, and saw this output:
> root@RCFA-1048515:~# dhcpcd --nobackground --broadcast --timeout 10 -d br0
> dhcpcd-9.3.2 starting
> chrooting as dhcpcd to /var/lib/dhcpcd
> sandbox: seccomp
> spawned master process on PID 917
> spawned privileged actioneer on PID 918
> spawned controller proxy on PID 919
> DUID 00:01:00:01:27:10:1b:c0:00:02:d9:1f:ff:c3
> br0: executing: /lib/dhcpcd/dhcpcd-run-hooks PREINIT
> br0: executing: /lib/dhcpcd/dhcpcd-run-hooks CARRIER
> br0: IAID d9:1f:ff:c3
> br0: delaying IPv4 for 0.6 seconds
> br0: reading lease: /var/db/dhcpcd/br0.lease
> br0: rebinding lease of 192.168.10.14
> br0: sending REQUEST (xid 0x857d13e9), next in 4.8 seconds
> br0: acknowledged 192.168.10.14 from 192.168.10.1
> br0: probing address 192.168.10.14/24
> br0: probing for 192.168.10.14
> br0: ARP probing 192.168.10.14 (1 of 3), next in 1.7 seconds
> br0: ARP probing 192.168.10.14 (2 of 3), next in 1.2 seconds
> br0: ARP probing 192.168.10.14 (3 of 3), next in 2.0 seconds
> br0: DAD completed for 192.168.10.14
> br0: leased 192.168.10.14 for 300 seconds
> br0: renew in 150 seconds, rebind in 262 seconds
> br0: writing lease: /var/db/dhcpcd/br0.lease
> br0: adding IP address 192.168.10.14/24 broadcast 192.168.10.255
> br0: adding route to 192.168.10.0/24
> br0: adding default route via 192.168.10.1
> br0: ARP announcing 192.168.10.14 (1 of 2), next in 2.0 seconds
> br0: executing: /lib/dhcpcd/dhcpcd-run-hooks BOUND
> spawned listener 192.168.10.14 on PID 953
> br0: ARP announcing 192.168.10.14 (2 of 2)
> ps_seccomp_violation: unexpected syscall 221 (arch=0x40000028)
>
> The unexpected syscall 221 correlates with attempting to dump the lease:
> root@RCFA-1048515:~# dhcpcd --dumplease -4 -d br0
> send OK
> dhcpcd_readdump0: Connection reset by peer
>
> Looks like it is a call to fnctl64. I added fnctl64 to ps_seccomp_filter, and tried again. This time dumping the lease failed with the a different message:
> root@RCFA-1048515:~# dhcpcd --dumplease -4 br0
> ps_seccomp_violation: unexpected syscall 197 (arch=0x40000028)
>
> Syscall 197 is fstat64, so I added that to the filter too and then was able to dump the lease successfully. I've attached the patch file that appears to work for us with privsep enabled.
>
> Thanks for the help.

Thanks for the patch!

Comitted here: 
https://roy.marples.name/cgit/dhcpcd.git/commit/?id=694cb5f7dc6a67008a09a6d1d6002c6154e7742d

Roy