The fwutil command will interpret the final 16 byte of a given firmware
image files as "struct fwimage_trailer".
In case these bytes do look like a valid trailer, we must ensure that we
print them out along with the remainder of the image to not accidentally
truncate non-trailer-images by 16 bytes when they're piped through fwtool,
e.g. as part of an image verification command sequence.
Some command sequences pipe images through fwtool in order to strip any
possible metadata, certificate or signature trailers and do not expect
bare images without any of that metadata to get truncated as other non-
fwtool specific metadata is expected at the end of the file, e.g. an
information block with an md5sum in case of the combined image format.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 889b841048c5eb7f975135cab363f1fdd9b6cfa1)
This allows extracing the firmware + metadata from a signed firmware without
altering the original image file
Signed-off-by: Felix Fietkau <nbd@nbd.name>
This will be used to append extra information to images which allows the
system to verify if an image is compatible with the system.
The extra data is appended to the end of the image, where it will be
ignored when upgrading from systems that do not process this data yet:
If the image is a squashfs or jffs2 image, the extra data will land
after the end-of-filesystem marker, where it will be overwritten once
the system boots for the first timee.
If the image is a sysupgrade tar file, tar will simply ignore the extra
data when unpacking.
The layout of the metadata/signature chunks is constructed in a way
that the last part contains just a magic and size information, so that
the tool can quickly check if any valid data is present without having
to do a pattern search throughout the full image.
Chunks also contain CRC32 information to detect file corruption, even
when the image is not signed.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Jo-Philipp Wich