[RFC PATCH 4/7] common/encrypt: add helper for ciphertext verification tests

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Introduce a function _verify_ciphertext_for_encryption_policy() which
verifies the correctness of encryption with the specified settings.

Basically, it does the following:

1. If missing any prerequisites, skip the test.

2. Create files in encrypted directories on the scratch device.

3. Unmount the scratch device and compare the actual ciphertext stored
   on-disk to the ciphertext computed by the fscrypt-crypt-util program.

Both file contents and names are verified, and non-default encryption
modes are supported.  Previously, non-default encryption modes were
untested by xfstests.  Also, while there's an existing test generic/399
that checks that encrypted contents seem random, it doesn't actually
test for correctness, nor does it test filenames encryption.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 common/encrypt | 390 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 390 insertions(+)

diff --git a/common/encrypt b/common/encrypt
index 37f16b94..3e48abc0 100644
--- a/common/encrypt
+++ b/common/encrypt
@@ -263,3 +263,393 @@ _get_encpolicy()
 
 	$XFS_IO_PROG -c "get_encpolicy $*" "$file"
 }
+
+# Retrieve the encryption nonce of the given inode as a hex string.  The nonce
+# was randomly generated by the filesystem and isn't exposed directly to
+# userspace.  But it can be read using the filesystem's debugging tools.
+_get_encryption_nonce()
+{
+	local device=$1
+	local inode=$2
+
+	case $FSTYP in
+	ext4)
+		# Use debugfs to dump the special xattr named "c", which is the
+		# file's fscrypt_context.  This produces a line like:
+		#
+		#	c (28) = 01 01 04 02 00 00 00 00 00 00 00 00 ef bd 18 76 5d f6 41 4e c0 a2 cd 5f 91 29 7e 12
+		#
+		# Then filter it to get just the 16-byte 'nonce' field at the end:
+		#
+		#	efbd18765df6414ec0a2cd5f91297e12
+		#
+		$DEBUGFS_PROG $device -R "ea_get <$inode> c" 2>>$seqres.full \
+			| grep '^c' | sed 's/^.*=//' | tr -d ' \n' | tail -c 32
+		;;
+	f2fs)
+		# dump.f2fs prints the fscrypt_context like:
+		#
+		#	xattr: e_name_index:9 e_name:c e_name_len:1 e_value_size:28 e_value:
+		#	format: 1
+		#	contents_encryption_mode: 0x1
+		#	filenames_encryption_mode: 0x4
+		#	flags: 0x2
+		#	master_key_descriptor: 0000000000000000
+		#	nonce: EFBD18765DF6414EC0A2CD5F91297E12
+		$DUMP_F2FS_PROG -i $inode $device | awk '
+			/\<e_name:c\>/ { found = 1 }
+			/^nonce:/ && found {
+				print substr($0, length($0) - 31, 32);
+				found = 0;
+			}'
+		;;
+	*)
+		_notrun "_get_encryption_nonce() isn't implemented on $FSTYP"
+		;;
+	esac
+}
+
+# Require support for _get_encryption_nonce()
+_require_get_encryption_nonce_support()
+{
+	echo "Checking for _get_encryption_nonce() support for $FSTYP" >> $seqres.full
+	case $FSTYP in
+	ext4)
+		_require_command "$DEBUGFS_PROG" debugfs
+		;;
+	f2fs)
+		_require_command "$DUMP_F2FS_PROG" dump.f2fs
+		;;
+	*)
+		_notrun "_get_encryption_nonce() isn't implemented on $FSTYP"
+		;;
+	esac
+}
+
+# Retrieve the filename stored on-disk for the given file.
+# The name is printed to stdout in binary.
+_get_on_disk_filename()
+{
+	local device=$1
+	local inode=$2
+	local dir_inode=$3
+
+	case $FSTYP in
+	ext4)
+		# Extract the filename from the debugfs output line like:
+		#
+		#  131075  100644 (1)      0      0       0 22-Apr-2019 16:54 \xa2\x85\xb0z\x13\xe9\x09\x86R\xed\xdc\xce\xad\x14d\x19
+		#
+		$DEBUGFS_PROG $device -R "ls -l -r <$dir_inode>" \
+					2>>$seqres.full | perl -ne '
+			next if not /^\s*'$inode'\s+/;
+			s/.*?\d\d:\d\d //;
+			chomp;
+			s/\\x([[:xdigit:]]{2})/chr hex $1/eg;
+			print;'
+		;;
+	f2fs)
+		# Extract the filename from the dump.f2fs output line like:
+		#
+		#  i_name                        		[UpkzIPuts9by1oDmE+Ivfw]
+		#
+		# The name is base64-encoded, so we have to decode it here.
+		#
+		$DUMP_F2FS_PROG $device -i $inode | perl -ne '
+			next if not /^i_name\s+\[([A-Za-z0-9+,]+)\]/;
+			chomp $1;
+			my @chars = split //, $1;
+			my $ac = 0;
+			my $bits = 0;
+			my $table = join "", (A..Z, a..z, 0..9, "+", ",");
+			foreach (@chars) {
+				$ac += index($table, $_) << $bits;
+				$bits += 6;
+				if ($bits >= 8) {
+					print chr($ac & 0xff);
+					$ac >>= 8;
+					$bits -= 8;
+				}
+			}
+			if ($ac != 0) {
+				print STDERR "Invalid base64-encoded string!\n";
+			}'
+		;;
+	*)
+		_notrun "_get_on_disk_filename() isn't implemented on $FSTYP"
+		;;
+	esac
+}
+
+# Require support for _get_on_disk_filename()
+_require_get_on_disk_filename_support()
+{
+	echo "Checking for _get_on_disk_filename() support for $FSTYP" >> $seqres.full
+	case $FSTYP in
+	ext4)
+		# Verify that the "ls -l -r" debugfs command is supported and
+		# hex-encodes non-ASCII characters, rather than using an
+		# ambiguous escaping method.  This requires the e2fsprogs patch
+		# "debugfs: avoid ambiguity when printing filenames"
+		# (https://marc.info/?l=linux-ext4&m=155596495624232&w=2).
+		# TODO: once merged, list the minimum e2fsprogs version here.
+		_require_command "$DEBUGFS_PROG" debugfs
+		_scratch_mount
+		touch $SCRATCH_MNT/$'\xc1'
+		_scratch_unmount
+		if ! $DEBUGFS_PROG $SCRATCH_DEV -R "ls -l -r /" 2>&1 \
+			| tee -a $seqres.full | grep -E -q '\s+\\xc1\s*$'; then
+			_notrun "debugfs (e2fsprogs) is too old; doesn't support showing unambiguous on-disk filenames"
+		fi
+		;;
+	f2fs)
+		# Verify that dump.f2fs shows encrypted filenames in full.  This
+		# requires the patch "f2fs-tools: improve filename printing"
+		# (https://sourceforge.net/p/linux-f2fs/mailman/message/36648641/).
+		# TODO: once merged, list the minimum f2fs-tools version here.
+
+		_require_command "$DUMP_F2FS_PROG" dump.f2fs
+		_require_command "$KEYCTL_PROG" keyctl
+		_scratch_mount
+		_new_session_keyring
+
+		local keydesc=$(_generate_encryption_key)
+		local dir=$SCRATCH_MNT/test.${FUNCNAME[0]}
+		local file=$dir/$(perl -e 'print "A" x 255')
+		mkdir $dir
+		_set_encpolicy $dir $keydesc
+		touch $file
+		local inode=$(stat -c %i $file)
+
+		_scratch_unmount
+		$KEYCTL_PROG clear @s
+
+		# 255-character filename should result in 340 base64 characters.
+		if ! $DUMP_F2FS_PROG -i $inode $SCRATCH_DEV \
+			| grep -E -q '^i_name[[:space:]]+\[[A-Za-z0-9+,]{340}\]'; then
+			_notrun "dump.f2fs (f2fs-tools) is too old; doesn't support showing unambiguous on-disk filenames"
+		fi
+		;;
+	*)
+		_notrun "_get_on_disk_filename() isn't implemented on $FSTYP"
+		;;
+	esac
+}
+
+# Get the file's list of on-disk blocks as a comma-separated list of block
+# offsets from the start of the device.  "Blocks" are 512 bytes each here.
+_get_file_block_list()
+{
+	local file=$1
+
+	sync
+	$XFS_IO_PROG -c fiemap $file | perl -ne '
+		next if not /^\s*\d+: \[\d+\.\.\d+\]: (\d+)\.\.(\d+)/;
+		print $_ . "," foreach $1..$2;' | sed 's/,$//'
+}
+
+# Dump a block list that was previously saved by _get_file_block_list().
+_dump_file_blocks()
+{
+	local device=$1
+	local blocklist=$2
+	local block
+
+	for block in $(tr ',' ' ' <<< $blocklist); do
+		dd if=$device bs=512 count=1 skip=$block status=none
+	done
+}
+
+_do_verify_ciphertext_for_encryption_policy()
+{
+	local contents_encryption_mode=$1
+	local filenames_encryption_mode=$2
+	local policy_flags=$3
+	local set_encpolicy_args=$4
+	local keydesc=$5
+	local raw_key_hex=$6
+	local crypt_cmd="src/fscrypt-crypt-util $7"
+
+	local blocksize=$(_get_block_size $SCRATCH_MNT)
+	local test_contents_files=()
+	local test_filenames_files=()
+	local i src dir dst inode blocklist \
+	      padding_flag padding dir_inode len name f nonce decrypted_name
+
+	# Create files whose encrypted contents we'll verify.  For each, save
+	# the information: (copy of original file, inode number of encrypted
+	# file, comma-separated block list) into test_contents_files[].
+	echo "Creating files for contents verification" >> $seqres.full
+	i=1
+	rm -f $tmp.testfile_*
+	for src in /dev/zero /dev/urandom; do
+		head -c $((4 * blocksize)) $src > $tmp.testfile_$i
+		(( i++ ))
+	done
+	dir=$SCRATCH_MNT/encdir
+	mkdir $dir
+	_set_encpolicy $dir $keydesc $set_encpolicy_args -f $policy_flags
+	for src in $tmp.testfile_*; do
+		dst=$dir/${src##*.}
+		cp $src $dst
+		inode=$(stat -c %i $dst)
+		blocklist=$(_get_file_block_list $dst)
+		test_contents_files+=("$src $inode $blocklist")
+	done
+
+	# Create files whose encrypted names we'll verify.  For each, save the
+	# information: (original filename, inode number of encrypted file, inode
+	# of parent directory, padding amount) into test_filenames_files[].  Try
+	# each padding amount: 4, 8, 16, or 32 bytes.  Also try various filename
+	# lengths, including boundary cases.  Assume NAME_MAX == 255.
+	echo "Creating files for filenames verification" >> $seqres.full
+	for padding_flag in 0 1 2 3; do
+		padding=$((4 << padding_flag))
+		dir=$SCRATCH_MNT/encdir.pad$padding
+		mkdir $dir
+		dir_inode=$(stat -c %i $dir)
+		_set_encpolicy $dir $keydesc $set_encpolicy_args \
+			-f $((policy_flags | padding_flag))
+		for len in 1 3 15 16 17 32 100 254 255; do
+			name=$(tr -d -C a-zA-Z0-9 < /dev/urandom | head -c $len)
+			touch $dir/$name
+			inode=$(stat -c %i $dir/$name)
+			test_filenames_files+=("$name $inode $dir_inode $padding")
+		done
+	done
+
+	# Now unmount the filesystem and verify the ciphertext we just wrote.
+	_scratch_unmount
+
+	echo "Verifying encrypted file contents" >> $seqres.full
+	for f in "${test_contents_files[@]}"; do
+		read -r src inode blocklist <<< "$f"
+		nonce=$(_get_encryption_nonce $SCRATCH_DEV $inode)
+		_dump_file_blocks $SCRATCH_DEV $blocklist > $tmp.actual_contents
+		$crypt_cmd $contents_encryption_mode $raw_key_hex \
+			--file-nonce=$nonce --block-size=$blocksize \
+			< $src > $tmp.expected_contents
+		if ! cmp $tmp.expected_contents $tmp.actual_contents; then
+			_fail "Expected encrypted contents != actual encrypted contents.  File: $f"
+		fi
+		$crypt_cmd $contents_encryption_mode $raw_key_hex --decrypt \
+			--file-nonce=$nonce --block-size=$blocksize \
+			< $tmp.actual_contents > $tmp.decrypted_contents
+		if ! cmp $src $tmp.decrypted_contents; then
+			_fail "Contents decryption sanity check failed.  File: $f"
+		fi
+	done
+
+	echo "Verifying encrypted file names" >> $seqres.full
+	for f in "${test_filenames_files[@]}"; do
+		read -r name inode dir_inode padding <<< "$f"
+		nonce=$(_get_encryption_nonce $SCRATCH_DEV $dir_inode)
+		_get_on_disk_filename $SCRATCH_DEV $inode $dir_inode \
+			> $tmp.actual_name
+		echo -n "$name" | \
+			$crypt_cmd $filenames_encryption_mode $raw_key_hex \
+			--file-nonce=$nonce --padding=$padding \
+			--block-size=255 > $tmp.expected_name
+		if ! cmp $tmp.expected_name $tmp.actual_name; then
+			_fail "Expected encrypted filename != actual encrypted filename.  File: $f"
+		fi
+		$crypt_cmd $filenames_encryption_mode $raw_key_hex --decrypt \
+			--file-nonce=$nonce --padding=$padding \
+			--block-size=255 < $tmp.actual_name \
+			> $tmp.decrypted_name
+		decrypted_name=$(tr -d '\0' < $tmp.decrypted_name)
+		if [ "$name" != "$decrypted_name" ]; then
+			_fail "Filename decryption sanity check failed ($name != $decrypted_name).  File: $f"
+		fi
+	done
+}
+
+_fscrypt_mode_name_to_num()
+{
+	local name=$1
+
+	case "$name" in
+	AES-256-XTS)		echo 1 ;; # FS_ENCRYPTION_MODE_AES_256_XTS
+	AES-256-CTS-CBC)	echo 4 ;; # FS_ENCRYPTION_MODE_AES_256_CTS
+	AES-128-CBC-ESSIV)	echo 5 ;; # FS_ENCRYPTION_MODE_AES_128_CBC
+	AES-128-CTS-CBC)	echo 6 ;; # FS_ENCRYPTION_MODE_AES_128_CTS
+	Adiantum)		echo 9 ;; # FS_ENCRYPTION_MODE_ADIANTUM
+	*)			_fail "Unknown fscrypt mode: $name" ;;
+	esac
+}
+
+# Verify that file contents and names are encrypted correctly when an encryption
+# policy of the specified type is used.
+#
+# The first two parameters are the contents and filenames encryption modes to
+# test.  Optionally, also specify 'direct' to test the DIRECT_KEY flag.
+_verify_ciphertext_for_encryption_policy()
+{
+	local contents_encryption_mode=$1
+	local filenames_encryption_mode=$2
+	local opt
+	local policy_flags=0
+	local set_encpolicy_args=""
+	local crypt_util_args=""
+
+	shift 2
+	for opt; do
+		case "$opt" in
+		direct)
+			if [ $contents_encryption_mode != \
+			     $filenames_encryption_mode ]; then
+				_fail "For direct key mode, contents and filenames modes must match"
+			fi
+			(( policy_flags |= 0x04 )) # FS_POLICY_FLAG_DIRECT_KEY
+			;;
+		*)
+			_fail "Unknown option '$opt' passed to ${FUNCNAME[0]}"
+			;;
+		esac
+	done
+	local contents_mode_num=$(_fscrypt_mode_name_to_num $contents_encryption_mode)
+	local filenames_mode_num=$(_fscrypt_mode_name_to_num $filenames_encryption_mode)
+
+	set_encpolicy_args+=" -c $contents_mode_num"
+	set_encpolicy_args+=" -n $filenames_mode_num"
+
+	if (( policy_flags & 0x04 )); then
+		crypt_util_args+=" --kdf=none"
+	else
+		crypt_util_args+=" --kdf=AES-128-ECB"
+	fi
+	set_encpolicy_args=${set_encpolicy_args# }
+
+	_require_scratch_encryption $set_encpolicy_args
+	_require_test_program "fscrypt-crypt-util"
+	_require_xfs_io_command "fiemap"
+	_require_get_encryption_nonce_support
+	_require_get_on_disk_filename_support
+	_require_command "$KEYCTL_PROG" keyctl
+
+	echo "Creating encryption-capable filesystem" >> $seqres.full
+	_scratch_mkfs_encrypted &>> $seqres.full
+	_scratch_mount
+
+	echo "Generating encryption key" >> $seqres.full
+	local raw_key=$(_generate_raw_encryption_key)
+	local keydesc=$(_generate_key_descriptor)
+	_new_session_keyring
+	_add_encryption_key $keydesc $raw_key
+	local raw_key_hex=$(echo "$raw_key" | tr -d '\\x')
+
+	echo
+	echo -e "Verifying ciphertext with parameters:"
+	echo -e "\tcontents_encryption_mode: $contents_encryption_mode"
+	echo -e "\tfilenames_encryption_mode: $filenames_encryption_mode"
+	[ $# -ne 0 ] && echo -e "\toptions: $*"
+
+	_do_verify_ciphertext_for_encryption_policy \
+		"$contents_encryption_mode" \
+		"$filenames_encryption_mode" \
+		"$policy_flags" \
+		"$set_encpolicy_args" \
+		"$keydesc" \
+		"$raw_key_hex" \
+		"$crypt_util_args"
+}
-- 
2.21.0.593.g511ec345e18-goog