6. Lập trình Bash shell + Can thiệp vào Linux kernel image

#!/bin/sh
# SPDX-License-Identifier: GPL-2.0-only
# ----------------------------------------------------------------------
# extract-vmlinux - Extract uncompressed vmlinux from a kernel image
#
# Inspired from extract-ikconfig
# (c) 2009,2010 Dick Streefland <dick@streefland.net>
#
# (c) 2011      Corentin Chary <corentin.chary@gmail.com>
#
# ----------------------------------------------------------------------

check_vmlinux()
{
	# Use readelf to check if it's a valid ELF
	# TODO: find a better to way to check that it's really vmlinux
	#       and not just an elf
	readelf -h $1 > /dev/null 2>&1 || return 1

	cat $1
	exit 0
}

try_decompress()
{
	# The obscure use of the "tr" filter is to work around older versions of
	# "grep" that report the byte offset of the line instead of the pattern.

	# Try to find the header ($1) and decompress from here
	for	pos in `tr "$1n$2" "n$2=" < "$img" | grep -abo "^$2"`
	do
		pos=${pos%%:*}
		tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
		check_vmlinux $tmp
	done
}

# Check invocation:
me=${0##*/}
img=$1
if	[ $# -ne 1 -o ! -s "$img" ]
then
	echo "Usage: $me <kernel-image>" >&2
	exit 2
fi

# Prepare temp files:
tmp=$(mktemp /tmp/vmlinux-XXX)
trap "rm -f $tmp" 0

# That didn't work, so retry after decompression.
try_decompress '3721310' xy    gunzip
try_decompress '3757zXZ00' abcde unxz
try_decompress 'BZh'          xy    bunzip2
try_decompress '135'   xxx   unlzma
try_decompress '211114132' xy    'lzop -d'
try_decompress '02!L30'   xxx   'lz4 -d'
try_decompress '(265/375'   xxx   unzstd

# Finally check for uncompressed images or objects:
check_vmlinux $img

# Bail out:
echo "$me: Cannot find vmlinux." >&2

#!/bin/sh
# ----------------------------------------------------------------------
# extract-ikconfig - Extract the .config file from a kernel image
#
# This will only work when the kernel was compiled with CONFIG_IKCONFIG.
#
# The obscure use of the "tr" filter is to work around older versions of
# "grep" that report the byte offset of the line instead of the pattern.
#
# (c) 2009,2010 Dick Streefland <dick@streefland.net>
# Licensed under the terms of the GNU General Public License.
# ----------------------------------------------------------------------

cf1='IKCFG_ST3721310'
cf2='0123456789'

dump_config()
{
	if	pos=`tr "$cf1n$cf2" "n$cf2=" < "$1" | grep -abo "^$cf2"`
	then
		pos=${pos%%:*}
		tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
		if	[ $? != 1 ]
		then	# exit status must be 0 or 2 (trailing garbage warning)
			cat $tmp1
			exit 0
		fi
	fi
}

try_decompress()
{
	for	pos in `tr "$1n$2" "n$2=" < "$img" | grep -abo "^$2"`
	do
		pos=${pos%%:*}
		tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
		dump_config $tmp2
	done
}

# Check invocation:
me=${0##*/}
img=$1
if	[ $# -ne 1 -o ! -s "$img" ]
then
	echo "Usage: $me <kernel-image>" >&2
	exit 2
fi

# Prepare temp files:
tmp1=/tmp/ikconfig$$.1
tmp2=/tmp/ikconfig$$.2
trap "rm -f $tmp1 $tmp2" 0

# Initial attempt for uncompressed images or objects:
dump_config "$img"

# That didn't work, so retry after decompression.
try_decompress '3721310' xy    gunzip
try_decompress '3757zXZ00' abcde unxz
try_decompress 'BZh'          xy    bunzip2
try_decompress '135'   xxx   unlzma
try_decompress '211114132' xy    'lzop -d'
try_decompress '024111430' xyy 'lz4 -d -l'
try_decompress '5026557375' xxx unzstd

# Bail out:
echo "$me: Cannot find kernel config." >&2
exit 1