[OpenWrt-Devel] Uncompress image: trailing garbage ignored

Rafał Miłecki zajec5 at gmail.com
Mon May 4 04:40:22 EDT 2020

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.

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