62 lines
1.6 KiB
Bash
62 lines
1.6 KiB
Bash
#!/bin/bash
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make_block_device_rw() {
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local block_dev="$1"
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[[ -b "${block_dev}" ]] || return 0
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if [[ $(sudo blockdev --getro "${block_dev}") == "1" ]]; then
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sudo blockdev --setrw "${block_dev}"
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fi
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}
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is_ext2_rw_mount_enabled() {
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local rootfs=$1
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local offset="${2-0}"
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local ro_compat_offset=$((0x464 + 3)) # Get 'highest' byte
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local ro_compat_flag=$(sudo dd if="${rootfs}" \
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skip=$((offset + ro_compat_offset)) bs=1 count=1 status=none \
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2>/dev/null | hexdump -e '1 "%.2x"')
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test "${ro_compat_flag}" = "00"
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}
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# Returns whether the passed rootfs is an extended filesystem by checking the
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# ext2 s_magic field in the superblock.
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is_ext_filesystem() {
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local rootfs=$1
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local offset="${2-0}"
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local ext_magic_offset=$((0x400 + 56))
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local ext_magic=$(sudo dd if="${rootfs}" \
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skip=$((offset + ext_magic_offset)) bs=1 count=2 2>/dev/null |
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hexdump -e '1/2 "%.4x"')
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test "${ext_magic}" = "ef53"
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}
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enable_rw_mount() {
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local rootfs=$1
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local offset="${2-0}"
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local ro_compat_offset=$((0x464 + 3)) # Set 'highest' byte
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is_ext_filesystem "${rootfs}" "${offset}" || return 0
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is_ext2_rw_mount_enabled "${rootfs}" "${offset}" && return 0
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make_block_device_rw "${rootfs}"
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printf '\000' |
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sudo dd of="${rootfs}" seek=$((offset + ro_compat_offset)) \
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conv=notrunc count=1 bs=1 status=none
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# Force all of the file writes to complete, in case it's necessary for
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# crbug.com/954188
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sync
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}
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usage() {
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echo "Usage: <Shim file>"
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}
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if [ "$(id -u)" -ne 0 ]
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then
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echo "Run as root"
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exit 0
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fi
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if [ $# -lt 1 ]
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then
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usage
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exit 0
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fi
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