common/verity

# SPDX-License-Identifier: GPL-2.0
# Copyright 2018 Google LLC
#
# Functions for setting up and testing fs-verity

# btrfs will return IO errors on corrupted data with or without fs-verity.
# to really test fs-verity, use nodatasum.
if [ "$FSTYP" == "btrfs" ]; then
        if [ -z "$MOUNT_OPTIONS" ]; then
                export MOUNT_OPTIONS="-o nodatasum"
        else
                export MOUNT_OPTIONS+=" -o nodatasum"
        fi
fi

# Require fs-verity support on the scratch filesystem.
#
# FSV_BLOCK_SIZE will be set to a Merkle tree block size that is supported by
# the filesystem.  Other sizes may be supported too, but FSV_BLOCK_SIZE is the
# only size that is guaranteed to work without any additional checks.
_require_scratch_verity()
{
	_require_scratch
	_require_command "$FSVERITY_PROG" fsverity

	if ! _scratch_mkfs_verity &>>$seqres.full; then
		# ext4: need e2fsprogs v1.44.5 or later (but actually v1.45.2+
		#       is needed for some tests to pass, due to an e2fsck bug)
		# f2fs: need f2fs-tools v1.11.0 or later
		_notrun "$FSTYP userspace tools don't support fs-verity"
	fi

	# Try to mount the filesystem.  If this fails then either the kernel
	# isn't aware of fs-verity, or the mkfs options were not compatible with
	# verity (e.g. ext4 with block size != PAGE_SIZE on old kernels).
	if ! _try_scratch_mount &>>$seqres.full; then
		_notrun "kernel is unaware of $FSTYP verity feature," \
			"or mkfs options are not compatible with verity"
	fi

	local fstyp=${1:-$FSTYP}
	local scratch_mnt=${2:-$SCRATCH_MNT}

	# The filesystem may be aware of fs-verity but have it disabled by
	# CONFIG_FS_VERITY=n.  Detect support via sysfs.
	if [ ! -e /sys/fs/$fstyp/features/verity ]; then
		_notrun "kernel $fstyp isn't configured with verity support"
	fi

	# Select a default Merkle tree block size for when tests don't
	# explicitly specify one.
	#
	# For consistency reasons, all 'fsverity' subcommands, including
	# 'fsverity enable', default to 4K Merkle tree blocks.  That's generally
	# not ideal for tests, since it's possible that the filesystem doesn't
	# support 4K blocks but does support another size.  Specifically, the
	# kernel originally supported only merkle_tree_block_size ==
	# fs_block_size == page_size, and later it was updated to support
	# merkle_tree_block_size <= min(fs_block_size, page_size).
	#
	# Therefore, we default to merkle_tree_block_size == min(fs_block_size,
	# page_size).  That maximizes the chance of verity actually working.
	local fs_block_size=$(_get_block_size $scratch_mnt)
	local page_size=$(_get_page_size)
	if (( fs_block_size <= page_size )); then
		FSV_BLOCK_SIZE=$fs_block_size
	else
		FSV_BLOCK_SIZE=$page_size
	fi

	# The filesystem may have fs-verity enabled but not actually usable by
	# default.  E.g., ext4 only supports verity on extent-based files, so it
	# doesn't work on ext3-style filesystems.  So, try actually using it.
	if ! _fsv_can_enable $scratch_mnt/tmpfile; then
		_notrun "$fstyp verity isn't usable by default with these mkfs options"
	fi

	_scratch_unmount
}

# Check for CONFIG_FS_VERITY_BUILTIN_SIGNATURES=y, as well as the userspace
# commands needed to generate certificates and add them to the kernel.
_require_fsverity_builtin_signatures()
{
	if [ ! -e /proc/sys/fs/verity/require_signatures ]; then
		_notrun "kernel doesn't support fs-verity builtin signatures"
	fi
	_require_command "$OPENSSL_PROG" openssl
	_require_command "$KEYCTL_PROG" keyctl
}

# Use the openssl program to generate a private key and a X.509 certificate for
# use with fs-verity built-in signature verification, and convert the
# certificate to DER format.
_fsv_generate_cert()
{
	local keyfile=$1
	local certfile=$2
	local certfileder=$3

	if ! $OPENSSL_PROG req -newkey rsa:4096 -nodes -batch -x509 \
			-keyout $keyfile -out $certfile &>> $seqres.full; then
		_fail "Failed to generate certificate and private key (see $seqres.full)"
	fi
	$OPENSSL_PROG x509 -in $certfile -out $certfileder -outform der
}

# Clear the .fs-verity keyring.
_fsv_clear_keyring()
{
	$KEYCTL_PROG clear %keyring:.fs-verity
}

# Load the given X.509 certificate in DER format into the .fs-verity keyring so
# that the kernel can use it to verify built-in signatures.
_fsv_load_cert()
{
	local certfileder=$1

	$KEYCTL_PROG padd asymmetric '' %keyring:.fs-verity \
		< $certfileder >> $seqres.full
}

# Disable mandatory signatures for fs-verity files, if they are supported.
_disable_fsverity_signatures()
{
	if [ -e /proc/sys/fs/verity/require_signatures ]; then
		_set_fsverity_require_signatures 0
	fi
}

# Enable mandatory signatures for fs-verity files.
# This assumes that _require_fsverity_builtin_signatures() was called.
_enable_fsverity_signatures()
{
	_set_fsverity_require_signatures 1
}

# Restore the original value of fs.verity.require_signatures, i.e. the value it
# had at the beginning of the test.
_restore_fsverity_signatures()
{
	if [ -n "$FSVERITY_SIG_CTL_ORIG" ]; then
		_set_fsverity_require_signatures "$FSVERITY_SIG_CTL_ORIG"
	fi
}

# Restore the previous value of fs.verity.require_signatures, i.e. the value it
# had just before it was last written to.
_restore_prev_fsverity_signatures()
{
	if [ -n "$FSVERITY_SIG_CTL_PREV" ]; then
		_set_fsverity_require_signatures "$FSVERITY_SIG_CTL_PREV"
	fi
}

_set_fsverity_require_signatures()
{
	local newval=$1
	local oldval=$(</proc/sys/fs/verity/require_signatures)
	FSVERITY_SIG_CTL_PREV=$oldval
	if [ -z "$FSVERITY_SIG_CTL_ORIG" ]; then
		FSVERITY_SIG_CTL_ORIG=$oldval
	fi
	echo "$newval" > /proc/sys/fs/verity/require_signatures
}

# Require userspace and kernel support for 'fsverity dump_metadata'.
# $1 must be a file with fs-verity enabled.
_require_fsverity_dump_metadata()
{
	local verity_file=$1
	local tmpfile=$tmp.require_fsverity_dump_metadata

	if _fsv_dump_merkle_tree "$verity_file" 2>"$tmpfile" >/dev/null; then
		return
	fi
	if grep -q "^ERROR: unrecognized command: 'dump_metadata'$" "$tmpfile"
	then
		_notrun "Missing 'fsverity dump_metadata' command"
	fi
	if grep -q "^ERROR: FS_IOC_READ_VERITY_METADATA failed on '.*': Inappropriate ioctl for device$" "$tmpfile"
	then
		_notrun "Kernel doesn't support FS_IOC_READ_VERITY_METADATA"
	fi
	_fail "Unexpected output from 'fsverity dump_metadata': $(<"$tmpfile")"
}

# Check for userspace tools needed to corrupt verity data or metadata.
_require_fsverity_corruption()
{
	_require_xfs_io_command "fiemap"
	if [ $FSTYP == "btrfs" ]; then
		_require_btrfs_corrupt_block "value"
	fi
}

_scratch_mkfs_verity()
{
	case $FSTYP in
	ext4|f2fs)
		_scratch_mkfs -O verity
		;;
	btrfs)
		_scratch_mkfs
		;;
	overlay)
		_scratch_mkfs # This relies on the scratch fs supporting verity
                ;;
	*)
		_notrun "No verity support for $FSTYP"
		;;
	esac
}

_scratch_mkfs_encrypted_verity()
{
	case $FSTYP in
	ext4)
		_scratch_mkfs -O encrypt,verity
		;;
	f2fs)
		# f2fs-tools as of v1.11.0 doesn't allow comma-separated
		# features with -O.  Instead -O must be supplied multiple times.
		_scratch_mkfs -O encrypt -O verity
		;;
	*)
		_notrun "$FSTYP not supported in _scratch_mkfs_encrypted_verity"
		;;
	esac
}

_fsv_scratch_begin_subtest()
{
	local msg=$1

	rm -rf "${SCRATCH_MNT:?}"/*
	echo -e "\n# $msg"
}

_fsv_dump_merkle_tree()
{
	$FSVERITY_PROG dump_metadata merkle_tree "$@"
}

_fsv_dump_descriptor()
{
	$FSVERITY_PROG dump_metadata descriptor "$@"
}

_fsv_dump_signature()
{
	$FSVERITY_PROG dump_metadata signature "$@"
}

_fsv_enable()
{
	local args=("$@")
	# If the caller didn't explicitly specify a Merkle tree block size, then
	# use FSV_BLOCK_SIZE.
	if ! [[ " $*" =~ " --block-size" ]]; then
		args+=("--block-size=$FSV_BLOCK_SIZE")
	fi
	$FSVERITY_PROG enable "${args[@]}"
}

_fsv_measure()
{
        $FSVERITY_PROG measure "$@" | awk '{print $1}'
}

_fsv_digest()
{
	local args=("$@")
	# If the caller didn't explicitly specify a Merkle tree block size, then
	# use FSV_BLOCK_SIZE.
	if ! [[ " $*" =~ " --block-size" ]]; then
		args+=("--block-size=$FSV_BLOCK_SIZE")
	fi
	$FSVERITY_PROG digest "${args[@]}" | awk '{print $1}'
}

_fsv_sign()
{
	local args=("$@")
	# If the caller didn't explicitly specify a Merkle tree block size, then
	# use FSV_BLOCK_SIZE.
	if ! [[ " $*" =~ " --block-size" ]]; then
		args+=("--block-size=$FSV_BLOCK_SIZE")
	fi
	$FSVERITY_PROG sign "${args[@]}"
}

# Generate a file, then enable verity on it.
_fsv_create_enable_file()
{
	local file=$1
	shift

	head -c $((FSV_BLOCK_SIZE * 2)) /dev/zero > "$file"
	_fsv_enable "$file" "$@"
}

_fsv_can_enable()
{
	local test_file=$1
	shift
	local params=("$@")

	_disable_fsverity_signatures
	rm -f $test_file
	head -c 4096 /dev/zero > $test_file
	_fsv_enable $test_file "${params[@]}" &>> $seqres.full
	local status=$?
	_restore_prev_fsverity_signatures
	rm -f $test_file
	return $status
}

#
# _fsv_scratch_corrupt_bytes - Write some bytes to a file, bypassing the filesystem
#
# Write the bytes sent on stdin to the given offset in the given file, but do so
# by writing directly to the extents on the block device, with the filesystem
# unmounted.  This can be used to corrupt a verity file for testing purposes,
# bypassing the restrictions imposed by the filesystem.
#
# The file is assumed to be located on $SCRATCH_DEV.
#
_fsv_scratch_corrupt_bytes()
{
	local file=$1
	local offset=$2
	local lstart lend pstart pend
	local dd_cmds=()
	local cmd

	_scratch_sync	# Sync to avoid unwritten extents

	cat > $tmp.bytes
	local end=$(( offset + $(_get_filesize $tmp.bytes ) ))

	# For each extent that intersects the requested range in order, add a
	# command that writes the next part of the data to that extent.
	while read -r lstart lend pstart pend; do
		lstart=$((lstart * 512))
		lend=$(((lend + 1) * 512))
		pstart=$((pstart * 512))
		pend=$(((pend + 1) * 512))

		if (( lend - lstart != pend - pstart )); then
			_fail "Logical and physical extent lengths differ for file '$file'"
		elif (( offset < lstart )); then
			_fail "Hole in file '$file' at byte $offset.  Next extent begins at byte $lstart"
		elif (( offset < lend )); then
			local len=$((lend - offset))
			local seek=$((pstart + (offset - lstart)))
			dd_cmds+=("head -c $len | dd of=$SCRATCH_DEV oflag=seek_bytes seek=$seek status=none")
			(( offset += len ))
		fi
	done < <($XFS_IO_PROG -r -c "fiemap $offset $((end - offset))" "$file" \
		 | _filter_xfs_io_fiemap)

	if (( offset < end )); then
		_fail "Extents of file '$file' ended at byte $offset, but needed until $end"
	fi

	# Execute the commands to write the data
	_scratch_unmount
	for cmd in "${dd_cmds[@]}"; do
		eval "$cmd"
	done < $tmp.bytes
	sync	# Sync to flush the block device's pagecache
	_scratch_mount
}

#
# _fsv_scratch_corrupt_merkle_tree - Corrupt a file's Merkle tree
#
# Like _fsv_scratch_corrupt_bytes(), but this corrupts the file's fs-verity
# Merkle tree.  The offset is given as a byte offset into the Merkle tree.
#
_fsv_scratch_corrupt_merkle_tree()
{
	local file=$1
	local offset=$2

	case $FSTYP in
	ext4|f2fs)
		# ext4 and f2fs store the Merkle tree after the file contents
		# itself, starting at the next 65536-byte aligned boundary.
		(( offset += ($(_get_filesize $file) + 65535) & ~65535 ))
		_fsv_scratch_corrupt_bytes $file $offset
		;;
	btrfs)
		local ino=$(stat -c '%i' $file)
		_scratch_unmount
		local byte=""
		while read -n 1 byte; do
			local ascii=$(printf "%d" "'$byte'")
			# This command will find a Merkle tree item for the inode (-I $ino,37,0)
			# in the default filesystem tree (-r 5) and corrupt one byte (-b 1) at
			# $offset (-o $offset) with the ascii representation of the byte we read
			# (-v $ascii)
			$BTRFS_CORRUPT_BLOCK_PROG -r 5 -I $ino,37,0 \
			       --value $ascii --offset $offset -b 1 $SCRATCH_DEV
			(( offset += 1 ))
		done
		_scratch_mount
		;;
	*)
		_fail "_fsv_scratch_corrupt_merkle_tree() unimplemented on $FSTYP"
		;;
	esac
}

_require_fsverity_max_file_size_limit()
{
	case $FSTYP in
	btrfs|ext4|f2fs)
		;;
	*)
		_notrun "$FSTYP does not store verity data past EOF; no special file size limit"
		;;
	esac
}

# Replace fs-verity digests, as formatted by the 'fsverity' tool, with <digest>.
# This function can be used by tests where fs-verity digests depend on the
# default Merkle tree block size (FSV_BLOCK_SIZE).
_filter_fsverity_digest()
{
	sed -E 's/\b(sha(256|512)):[a-f0-9]{64,}\b/\1:<digest>/'
}