[Buildroot] [git commit] busybox: udhcpc.script: fix resolv.conf handling with multiple interfaces

[Arnout Vandecappelle <arnout@mind.be>]

On 26/06/13 15:20, Peter Korsgaard wrote:
> commit: http://git.buildroot.net/buildroot/commit/?id=584f418ec1ae3f0b5e09c10133c82578d78a3e03
> branch: http://git.buildroot.net/buildroot/commit/?id=refs/heads/master
>
> When udhcpc is used on multiple network devices at the same time (or a mix
> of dhcp and fixed configuration), /etc/resolv.conf should contain the
> union of information from all the interfaces.
>
> Currently that's not the case. The udhcpc script simply overwrites
> resolv.conf with the information from the specific interface on each dhcp
> bound/renew event.
>
> Fix it by tagging lines with the interface they came from when added,
> and drop the affected lines on deconfig/renew. As /etc/resolv.conf is
> often a symlink to /tmp (and rootfs might be read only), special care
> has to be taken when it is updated.
>
> Notice that I'm not really aware of any official documentation requiring
> that '#' comments in /etc/resolv.conf must be supported, but atleast
> glibc and uClibc do.
>
> Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
> ---
>   package/busybox/udhcpc.script |   19 ++++++++++++++++---
>   1 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/package/busybox/udhcpc.script b/package/busybox/udhcpc.script
> index f7beb56..43742fb 100755
> --- a/package/busybox/udhcpc.script
> +++ b/package/busybox/udhcpc.script
> @@ -13,6 +13,13 @@ case "$1" in
>   		/sbin/ifconfig $interface up
>   		/sbin/ifconfig $interface 0.0.0.0
>
> +		# drop info from this interface
> +		# resolv.conf may be a symlink to /tmp/, so take care
> +		TMPFILE=$(mktemp)
> +		grep -vE "# $interface\$" $RESOLV_CONF > $TMPFILE
> +		cat $TMPFILE > $RESOLV_CONF

  Isn't the non-atomicity of this line a potential race condition?

mv -f $TMPFILE $(readlink -f $RESOLV_CONF)

might be a better idea.


  Regards,
  Arnout

> +		rm -f $TMPFILE
> +
>   		if [ -x /usr/sbin/avahi-autoipd ]; then
>   			/usr/sbin/avahi-autoipd -k $interface
>   		fi
> @@ -41,11 +48,17 @@ case "$1" in
>   			done
>   		fi
>
> -		echo -n > $RESOLV_CONF
> -		[ -n "$domain" ] && echo search $domain >> $RESOLV_CONF
> +		# drop info from this interface
> +		# resolv.conf may be a symlink to /tmp/, so take care
> +		TMPFILE=$(mktemp)
> +		grep -vE "# $interface\$" $RESOLV_CONF > $TMPFILE
> +		cat $TMPFILE > $RESOLV_CONF
> +		rm -f $TMPFILE
> +
> +		[ -n "$domain" ] && echo "search $domain # $interface" >> $RESOLV_CONF
>   		for i in $dns ; do
>   			echo adding dns $i
> -			echo nameserver $i >> $RESOLV_CONF
> +			echo "nameserver $i # $interface" >> $RESOLV_CONF
>   		done
>   		;;
>   esac
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>


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
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