[OpenWrt-Devel] Uncompress image: trailing garbage ignored

Matthias Schiffer mschiffer at universe-factory.net
Sat May 23 07:51:46 EDT 2020

On 5/4/20 10:40 AM, Rafał Miłecki wrote:
> On 27.04.2020 00:48, Paul Spooren wrote:
>> On Thu, 2020-04-23 at 23:29 +0300, Hannu Nyman wrote:
>>> W. Michael Petullo kirjoitti 23.4.2020 klo 19.50:
>>>> I have started to notice a gunzip warning when decompressing the
>>>> OpenWrt images I build. This is with master df27e949:
>>>> gunzip  openwrt/bin/targets/x86/64/openwrt-x86-64-generic-ext4-
>>>> combined.img.gz -c >/dev/null
>>>> gzip: openwrt-aquinas-git/bin/targets/x86/64/openwrt-x86-64-generic-
>>>> ext4-combined.img.gz: decompression OK, trailing garbage ignored
>>>> Aside from the warning, gunzip exits with a code of 2. The gunzip man
>>>> page indicates that an exit code of 2 indicates a warning.
>>>> Is this a result of an intended change? Should I expect this to
>>>> continue? Are we sneaking a hash or signature in there? If so, I
>>>> suppose I will adjust some of the scripts I use to account for the
>>>> non-zero exit code.
>>> Likely we are attaching a signature since commit f81412160 a week ago:
>>> https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=f814121600e5cf43fd75fe93e5b1b54f65b71bcd
>> The sysupgrade process automatically handels compressed images, however the
>> validation does not. Currently fwtool validation in /usr/lib/fwtool.sh
>> reads the
>> sysupgrade(.gz) as is:
>> if ! fwtool -q -s /tmp/sysupgrade.ucert "$1"; then
>> A fix could be to use "append-metadata | gzip" for the firmware images
>> and then
>> unpack the firmware before validating it's signature and metadata, e.g.
>> with the
>> following command in fwtool.sh
>> source /usr/bin/common.sh
>> if ! get_image "$1" | fwtool -q -s /tmp/sysupgrade.ucert -; then
>> This worked in my qemu test, not tested on a real hardware.
>> Rafał Miłecki worked recently on the validation, maybe he can share an
>> opinion.
> My work didn't involve touching fwtool / metadata so unfortunately I
> cannot help with that.

A simple fix that is also in line with what we do on other targets would be
to provide separate factory and sysupgrade images on x86 as well. Only
factory would be meant to be unpacked manually, and only sysupgrade would
have metadata appended.


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