[Dnsmasq-discuss] Fwd: no-ping
Simon Kelley
simon at thekelleys.org.uk
Tue Feb 20 09:21:46 UTC 2024
Ah, this is working because you include --dhcp-broadcast, which avoids
the ARP-cache access.
I'm not clear why you want to avoid CAP_NET_ADMIN, but a correct patch
to do that would only not set need_cap_netadmin when --broadcast is set,
and only when it's set unconditionally, without tags.
Cheers,
Simon.
On 20/02/2024 00:50, Martin Ivičič wrote:
> I'm currently running dnsmasq (with my patch applied) using the following script and everything seems to work fine actually - no errors reported.
> (I have only added CAP_NET_BIND_SERVICE in order to be able to bind to port 67.)
>
> #!/bin/bash
> set -euo pipefail
> SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
>
> PID_FILE=$SCRIPT_DIR/dnsmasq.pid
>
> dnsmasq \
> --pid-file=$PID_FILE \
> --dhcp-leasefile=$SCRIPT_DIR/dnsmasq.leases \
> --strict-order \
> --bind-interfaces \
> --dhcp-authoritative \
> --no-ping \
> --dhcp-broadcast \
> --port=0 \
> --conf-file= \
> --no-hosts \
> --interface=br-mgmt \
> --listen-address=10.0.0.254 \
> --dhcp-range=net:mgmt,10.0.0.1,10.0.0.250,255.255.255.0,10.0.0.255 \
> --dhcp-option=mgmt,option:router \
> --dhcp-host=52:54:00:00:00:01,id:*,net:mgmt,10.0.0.1 \
> --dhcp-host=52:54:00:00:00:02,id:*,net:mgmt,10.0.0.2 \
> --dhcp-host=52:54:00:00:00:03,id:*,net:mgmt,10.0.0.3 \
> \
> --interface=br-dth \
> --listen-address=10.0.1.254 \
> --dhcp-range=net:dth,10.0.1.1,10.0.1.250,255.255.255.0,10.0.1.255 \
> --dhcp-option=dth,option:router \
> --dhcp-option=dth,option:classless-static-route,10.235.0.0/16,10.0.1.254 <http://10.235.0.0/16,10.0.1.254> \
> --dhcp-host=52:54:00:00:01:01,id:*,net:dth,10.0.1.1 \
> --dhcp-host=52:54:00:00:01:02,id:*,net:dth,10.0.1.2 \
> --dhcp-host=52:54:00:00:01:03,id:*,net:dth,10.0.1.3 \
> \
> --interface=br-inet \
> --listen-address=10.0.2.254 \
> --dhcp-range=net:inet,10.0.2.1,10.0.2.250,255.255.255.0,10.0.2.255 \
> --dhcp-option=inet,option:router,10.0.2.254 \
> --dhcp-host=52:54:00:00:02:01,id:*,net:inet,10.0.2.1 \
> --dhcp-host=52:54:00:00:02:02,id:*,net:inet,10.0.2.2 \
> --dhcp-host=52:54:00:00:02:03,id:*,net:inet,10.0.2.3 \
> \
> --no-daemon
>
>
> this is the output:
>
> dnsmasq: started, version 2.90deb2-1-g1ed783b DNS disabled
> dnsmasq: compile time options: IPv6 GNU-getopt no-DBus no-UBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset no-nftset auth no-cryptohash no-DNSSEC loop-detect inotify dumpfile
> dnsmasq-dhcp: DHCP, IP range 10.0.2.1 -- 10.0.2.250, lease time 1h
> dnsmasq-dhcp: DHCP, IP range 10.0.1.1 -- 10.0.1.250, lease time 1h
> dnsmasq-dhcp: DHCP, IP range 10.0.0.1 -- 10.0.0.250, lease time 1h
> dnsmasq-dhcp: DHCPDISCOVER(br-mgmt) 52:54:00:00:00:01
> dnsmasq-dhcp: DHCPOFFER(br-mgmt) 10.0.0.1 52:54:00:00:00:01
> dnsmasq-dhcp: DHCPDISCOVER(br-dth) 52:54:00:00:01:01
> dnsmasq-dhcp: DHCPOFFER(br-dth) 10.0.1.1 52:54:00:00:01:01
> dnsmasq-dhcp: DHCPDISCOVER(br-inet) 52:54:00:00:02:01
> dnsmasq-dhcp: DHCPOFFER(br-inet) 10.0.2.1 52:54:00:00:02:01
> dnsmasq-dhcp: DHCPREQUEST(br-mgmt) 10.0.0.1 52:54:00:00:00:01
> dnsmasq-dhcp: DHCPACK(br-mgmt) 10.0.0.1 52:54:00:00:00:01
> dnsmasq-dhcp: DHCPREQUEST(br-inet) 10.0.2.1 52:54:00:00:02:01
> dnsmasq-dhcp: DHCPACK(br-inet) 10.0.2.1 52:54:00:00:02:01
> dnsmasq-dhcp: DHCPREQUEST(br-dth) 10.0.1.1 52:54:00:00:01:01
> dnsmasq-dhcp: DHCPACK(br-dth) 10.0.1.1 52:54:00:00:01:01
>
>
> inside the VM:
>
> root at localhost:~# ip addr
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
> link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> inet127.0.0.1/8 <http://127.0.0.1/8> scope host lo
> valid_lft forever preferred_lft forever
> 2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:00:00:01 brd ff:ff:ff:ff:ff:ff
> inet10.0.0.1/24 <http://10.0.0.1/24> metric 1024 brd 10.0.0.255 scope global dynamic enp0s1
> valid_lft 3525sec preferred_lft 3525sec
> 3: enp0s2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:00:01:01 brd ff:ff:ff:ff:ff:ff
> inet10.0.1.1/24 <http://10.0.1.1/24> metric 1024 brd 10.0.1.255 scope global dynamic enp0s2
> valid_lft 3525sec preferred_lft 3525sec
> 4: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:00:02:01 brd ff:ff:ff:ff:ff:ff
> inet10.0.2.1/24 <http://10.0.2.1/24> metric 1024 brd 10.0.2.255 scope global dynamic enp0s3
> valid_lft 3525sec preferred_lft 3525sec
>
>
> Best regards,
> Martin
>
>
> On Tue, Feb 20, 2024 at 1:46 AM Simon Kelley <simon at thekelleys.org.uk
> <mailto:simon at thekelleys.org.uk>> wrote:
>
> If you're doing DHCP, even if you're not sending ICMP ping packets, you
> still need CAP_NET_ADMIN, because the DHCP server has to be able to
> manipulate the ARP table.
>
> I guess you're starting dnsmasq without CAP_NET_ADMIN, dnsmasq is
> determining that it needs CPA_NET_ADMIN to run the DHCP server, and
> erroring out because it doesn't have it.
>
>
> Simon.
>
>
> On 19/02/2024 15:32, Martin Ivičič wrote:
> > Hello,
> >
> > I might have stumbled upon a minor bug in dnsmasq which causes
> NET_ADMIN
> > capability being required even if it's actually not needed
> (according to
> > provided command line arguments).
> >
> > diff --git a/src/dnsmasq.c b/src/dnsmasq.c
> > index 30fb419..cef42f6 100644
> > --- a/src/dnsmasq.c
> > +++ b/src/dnsmasq.c
> > @@ -313,9 +313,10 @@ int main (int argc, char **argv)
> > {
> > dhcp_init();
> > # ifdef HAVE_LINUX_NETWORK
> > - if (!option_bool(OPT_NO_PING))
> > - need_cap_net_raw = 1;
> > - need_cap_net_admin = 1;
> > + if (!option_bool(OPT_NO_PING)) {
> > + need_cap_net_raw = 1;
> > + need_cap_net_admin = 1;
> > + }
> > # endif
> > }
> >
> > Without this patch, with following arguments, dnsmasq ends with
> > "dnsmasq: process is missing required capability NET_ADMIN"
> >
> > src/dnsmasq \
> > --strict-order \
> > --bind-interfaces \
> > --interface=br-mgmt \
> > --listen-address=10.0.0.254 \
> > --dhcp-range=10.0.0.1,10.0.0.250 \
> > --dhcp-authoritative \
> > --no-ping \
> > --dhcp-broadcast \
> > --port=0 \
> > --conf-file= \
> > --pid-file=/tmp/dnsmasq.pid \
> > --dhcp-leasefile=/tmp/dnsmasq.leases \
> > --dhcp-no-override \
> > --no-daemon
> >
> > After applying the patch dnsmasq starts and runs fine.
> >
> > Best regards,
> > Martin
> >
> >
> > _______________________________________________
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> > Dnsmasq-discuss at lists.thekelleys.org.uk
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> >
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>
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