2 # SPDX-License-Identifier: GPL-2.0
3 # Copyright (c) 2016 Google, Inc. All Rights Reserved.
5 # FS QA Test generic/399
7 # Check for weaknesses in filesystem encryption involving the same ciphertext
8 # being repeated. For file contents, we fill a small filesystem with large
9 # files of 0's and verify the filesystem is incompressible. For filenames, we
10 # create an identical symlink in two different directories and verify the
11 # ciphertext filenames and symlink targets are different.
13 # This test can detect some basic cryptographic mistakes such as nonce reuse
14 # (across files), initialization vector reuse (across blocks), or data somehow
15 # being left in plaintext by accident. For example, it detects the
16 # initialization vector reuse bug fixed in commit 02fc59a0d28f ("f2fs/crypto:
17 # fix xts_tweak initialization").
20 seqres=$RESULT_DIR/$seq
21 echo "QA output created by $seq"
25 status=1 # failure is the default!
26 trap "_cleanup; exit \$status" 0 1 2 3 15
34 # get standard environment, filters and checks
39 # remove previous $seqres.full before test
42 # real QA test starts here
45 _require_scratch_encryption
46 _require_command "$XZ_PROG" xz
47 _require_command "$KEYCTL_PROG" keyctl
52 # Set up a small filesystem containing an encrypted directory. 64 MB is enough
53 # for both ext4 and f2fs (f2fs doesn't support a 32 MB filesystem). Before
54 # creating the filesystem, zero out the needed portion of the device so that
55 # existing data on the device doesn't contribute to the compressed size.
58 fs_size=$((fs_size_in_mb * 1024 * 1024))
59 dd if=/dev/zero of=$SCRATCH_DEV bs=$((1024 * 1024)) \
60 count=$fs_size_in_mb &>> $seqres.full
61 _scratch_mkfs_sized_encrypted $fs_size &>> $seqres.full
64 keydesc=$(_generate_encryption_key)
65 mkdir $SCRATCH_MNT/encrypted_dir
66 _set_encpolicy $SCRATCH_MNT/encrypted_dir $keydesc
68 # Create the "same" symlink in two different directories.
69 # Later we'll check both the name and target of the symlink.
70 mkdir $SCRATCH_MNT/encrypted_dir/subdir1
71 mkdir $SCRATCH_MNT/encrypted_dir/subdir2
72 ln -s symlink_target $SCRATCH_MNT/encrypted_dir/subdir1/symlink
73 ln -s symlink_target $SCRATCH_MNT/encrypted_dir/subdir2/symlink
76 # Write files of 1 MB of all the same byte until we hit ENOSPC. Note that we
77 # must not create sparse files, since the contents of sparse files are not
78 # stored on-disk. Also, we create multiple files rather than one big file
79 # because we want to test for reuse of per-file keys.
84 file=$SCRATCH_MNT/encrypted_dir/file$i
85 if ! $XFS_IO_PROG -f $file -c 'pwrite 0 1M' &> $tmp.out; then
86 if ! grep -q 'No space left on device' $tmp.out; then
87 echo "FAIL: unexpected pwrite failure"
89 elif [ -e $file ]; then
90 total_file_size=$((total_file_size + $(stat -c %s $file)))
94 total_file_size=$((total_file_size + $(stat -c %s $file)))
96 if [ $i -gt $fs_size_in_mb ]; then
97 echo "FAIL: filesystem never filled up!"
102 # We shouldn't have been able to write more data than we had space for.
103 if (( $total_file_size > $fs_size )); then
104 echo "FAIL: wrote $total_file_size bytes but should have only" \
105 "had space for $fs_size bytes at most"
109 # Unmount the filesystem and compute its compressed size. It must be no smaller
110 # than the amount of data that was written; otherwise there was a compromise in
111 # the confidentiality of the data. False positives should not be possible
112 # because filesystem metadata will also contribute to the compressed size.
114 # Note: it's important to use a strong compressor such as xz which can detect
115 # redundancy across most or all of the filesystem. We run xz with a 64 MB
116 # sliding window but use some custom settings to make it faster and use less
117 # memory than the '-9' preset. The memory needed with our settings will be
118 # 64 * 6.5 = 416 MB; see xz(1).
120 _unlink_encryption_key $keydesc
122 fs_compressed_size=$(head -c $fs_size $SCRATCH_DEV | \
123 xz --lzma2=dict=64M,mf=hc4,mode=fast,nice=16 | \
126 if (( $fs_compressed_size < $total_file_size )); then
127 echo "FAIL: filesystem was compressible" \
128 "($total_file_size bytes => $fs_compressed_size bytes)"
130 echo "PASS: ciphertexts were not repeated for contents"
133 # Verify that encrypted filenames and symlink targets were not reused. Note
134 # that since the ciphertexts should be unpredictable, we cannot simply include
135 # the expected names in the expected output file.
137 find $SCRATCH_MNT/encrypted_dir -type l | wc -l
138 link1=$(find $SCRATCH_MNT/encrypted_dir -type l | head -1)
139 link2=$(find $SCRATCH_MNT/encrypted_dir -type l | tail -1)
140 [ $(basename $link1) = $(basename $link2) ] && \
141 echo "Encrypted filenames were reused!"
142 [ $(readlink $link1) = $(readlink $link2) ] && \
143 echo "Encrypted symlink targets were reused!"