[PATCH initramfs-tools 2/3] lsinitramfs: Parse and list files that include early microcode

[Ben Hutchings]

Look for uncompressed cpio headers and padding at the start of the
initramfs image.  If present, pass the initramfs directly to cpio
and then try to decompress a second cpio archive after the padding.

Closes: #717805
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
Thanks: Brett Parker <idu...@sommitrealweird.co.uk>
Thanks: Olivier Berger <olivier.ber...@telecom-sudparis.eu>
---
 lsinitramfs | 51 +++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 47 insertions(+), 4 deletions(-)

diff --git a/lsinitramfs b/lsinitramfs
index db179ca..0f25688 100755
--- a/lsinitramfs
+++ b/lsinitramfs
@@ -51,19 +51,62 @@ listarchive()
                bzip2 -c -d "${archive}" | cpio ${cpio_args}
        elif lzop -t "${archive}" >/dev/null 2>&1 ; then
                lzop -c -d "${archive}" | cpio ${cpio_args}
-       elif file "$initramfs" 2>/dev/null | grep -q "cpio archive" ; then
-               echo "lsinitramfs does not yet support cpio archive initramfs 
files." >&2
-               echo "See http://bugs.debian.org/717805 for more information." 
>&2
        fi
 }
 
+# Read bytes out of a file, checking that they are valid hex digits
+readhex()
+{
+       dd < "$1" bs=1 skip="$2" count="$3" status=none | \
+               LANG=C grep -E "^[0-9A-Fa-f]{$3}\$"
+}
+
+# Check for a zero byte in a file
+checkzero()
+{
+       dd < "$1" bs=1 skip="$2" count=1 status=none | \
+               LANG=C grep -q -z '^$'
+}
+
 for initramfs in "$@" ; do
        if ! [ -r "${initramfs}" ] ; then
                echo "Specified file could not be read." >&2
                exit 1
        else
                echo "${initramfs}"
-               listarchive "${initramfs}"
+
+               # There may be a prepended uncompressed archive.  cpio
+               # won't tell us the true size of this so we have to
+               # parse the headers and padding ourselves.  This is
+               # very roughly based on linux/lib/earlycpio.c
+               offset=0
+               while true; do
+                       if checkzero "$initramfs" $offset; then
+                               offset=$((offset + 4))
+                               continue
+                       fi
+                       magic="$(readhex "$initramfs" $offset 6)" || break
+                       test $magic = 070701 || test $magic = 070702 || break
+                       namesize=0x$(readhex "$initramfs" $((offset + 94)) 8)
+                       filesize=0x$(readhex "$initramfs" $((offset + 54)) 8)
+                       offset=$(((offset + 110)))
+                       offset=$(((offset + $namesize + 3) & ~3))
+                       offset=$(((offset + $filesize + 3) & ~3))
+               done
+
+               if [ $offset -ne 0 ]; then
+                       # List uncompressed archive
+                       cpio ${cpio_args} < "$initramfs"
+
+                       # List main archive
+                       subarchive=$(mktemp 
${TMPDIR:-/var/tmp}/lsinitramfs_XXXXXX)
+                       trap "rm -f $subarchive" EXIT
+                       dd < "$initramfs" bs="$offset" skip=1 status=none \
+                               > $subarchive
+                       listarchive $subarchive
+               else
+                       listarchive "${initramfs}"
+               fi
 
        fi
 done


-- 
Ben Hutchings
The two most common things in the universe are hydrogen and stupidity.

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