FS#785 - dnsmasq: /tmp/resolv.conf not set to localhost when noresolv=1 and resolvfile is unset #6597
Comments
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por: A patch with a fix has been posted on the dev mailing list. |
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por: In the end to fix this issue
The patch and the PR make sure that resolv.conf is managed by the resolver instance if and only if it owns 127.0.0.1#53. The dnsmasq patch also makes the handling of resolvfile independent of the value of noresolv. |
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por: The dnsmasq init patch submitted was discussed by @jow and @dedeckeh and they decided to not merge the patch because:
A possible fix for the port rewrite use-case has been proposed (an extra UCI option) and for the atomicity issue none truly but the changes that issue (also with the current version) occurs seems small. After this another v5 of the patch was submitted that changed some minor issues, but did not solve the two issues above. Related to the issue of atomicity of setting resolv.conf is likely another issue, that of synchronisation of setting the resolv.conf file only after the resolver really has been started. Currently no such thing is guaranteed after the call to procd_close_instance(). Also see [[http://lists.infradead.org/pipermail/lede-dev/2017-July/008249.html|[LEDE-DEV] Procd questions]] |
por:
For up-stream name resolution dnsmasq normally uses the name servers in the resolvfile, unless noresolv is true (and then a up-stream DNS server should explicitly have been configured).
The file /etc/resolv.conf defines the name servers to be used by processes that run on the router. This file is a soft link to /tmp/resolv.conf.
The dnsmasq init script dnsmasq_start() routine normally writes the file /tmp/resolv.conf and sets the name server to 127.0.0.1; the dnsmasq_stop() routine restores /tmp/resolv.conf to its previous state (being a soft link to /tmp/resolv.conf.auto)
These init script routines execute these steps only when UCI dhcp.dnsmasq.resolvfile equals '/tmp/resolv.conf.auto', but resolvfile only defaults to that value when UCI dhcp.dnsmasq.noresolv is not set to '1'.
Not using the local running DNS service when noresolv is true does not make sence; the semantics of that config value do not imply this.
The latter may typically occur when using unbound as DNS service with dnsmasq as dpcp-link (see unbound documentation).
work-around: explicitly set UCI dhcp.dnsmasq.resolvfile to '/tmp/resolv.conf.auto'.
possible fixes:
Write (and restore) /tmp/resolv.conf also when noresolv is true, e.g. guard it with:
[ "$noreolv" -eq '1' -o "$resolvfile" = "/tmp/resolv.conf.auto" ]or, probably a better fix, just test if a service runs on 127.0.0.1:53; advise on how to accomplish that are welcome.
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