* [PATCH] exfat/001: test that rename and move preserve benign secondary entries
@ 2026-07-23 4:11 Rochan Avlur
2026-08-12 18:06 ` Zorro Lang
0 siblings, 1 reply; 2+ messages in thread
From: Rochan Avlur @ 2026-07-23 4:11 UTC (permalink / raw)
To: fstests; +Cc: linkinjeon, Yuezhang.Mo, zlang, Rochan Avlur
Verify that unrecognized benign secondary directory entries (such as
vendor extensions) survive same-directory rename, cross-directory move,
in-place rename to a shorter name, rename overwriting an existing file,
and operations on files with multiple benign entries.
exFAT spec section 8.2 [1] requires implementations to preserve benign
secondary entries they do not recognize. This is a regression test for
kernel commit 8258ef28001a ("exfat: handle unreconized benign secondary
entries") which incorrectly freed benign entry clusters in the rename
and move paths.
[1]: https://learn.microsoft.com/en-us/windows/win32/fileio/exfat-specification#8-implementation-notes
Signed-off-by: Rochan Avlur <rochan.avlur@gmail.com>
---
src/Makefile | 3 +-
src/exfat_inject_vendor_ext.py | 155 ++++++++++++++++++++++++++++++
src/exfat_verify_vendor_ext.py | 62 ++++++++++++
tests/exfat/001 | 171 +++++++++++++++++++++++++++++++++
tests/exfat/001.out | 6 ++
tests/exfat/Makefile | 23 +++++
6 files changed, 419 insertions(+), 1 deletion(-)
create mode 100755 src/exfat_inject_vendor_ext.py
create mode 100755 src/exfat_verify_vendor_ext.py
create mode 100755 tests/exfat/001
create mode 100644 tests/exfat/001.out
create mode 100644 tests/exfat/Makefile
diff --git a/src/Makefile b/src/Makefile
index 31ac43b2..a42cf96f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -40,7 +40,8 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
btrfs_crc32c_forged_name.py popdir.pl popattr.py \
- soak_duration.awk parse-dev-tree.awk parse-free-space.py
+ soak_duration.awk parse-dev-tree.awk parse-free-space.py \
+ exfat_inject_vendor_ext.py exfat_verify_vendor_ext.py
SUBDIRS = log-writes perf
diff --git a/src/exfat_inject_vendor_ext.py b/src/exfat_inject_vendor_ext.py
new file mode 100755
index 00000000..81350da8
--- /dev/null
+++ b/src/exfat_inject_vendor_ext.py
@@ -0,0 +1,155 @@
+#!/usr/bin/python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Inject vendor extension (0xE0) benign secondary entries into an exFAT
+# directory entry set on an unmounted filesystem image or block device.
+#
+# Usage: exfat_inject_vendor_ext.py <device> <marker> <filename> [count]
+#
+# Adds <count> (default 1) vendor_ext entries carrying <marker> into the
+# entry set of <filename>. The marker is stored in the custom-defined
+# area so it can be verified after kernel operations.
+#
+# exFAT on-disk directory entry layout (each entry is 32 bytes):
+#
+# Entry set for a file:
+# [0] File entry (type 0x85)
+# byte 1: num_ext (number of secondary entries following)
+# bytes 2-3: entry set checksum (covers all entries, skipping these bytes)
+# [1] Stream extension (type 0xC0)
+# byte 3: name_len (filename length in Unicode characters)
+# bytes 4-7: name_hash
+# [2..N] Filename entries (type 0xC1, each holds up to 15 UTF-16LE chars)
+# bytes 2-31: 15 UTF-16LE characters
+# [N+1..] Benign secondary entries (type 0xA0-0xFF, e.g. vendor_ext 0xE0)
+# Implementations MUST preserve these even if unrecognized (spec s8.2)
+#
+# Vendor extension entry (type 0xE0):
+# byte 0: 0xE0 (entry type)
+# bytes 2-15: vendor GUID (we store our marker here)
+# bytes 18-31: vendor-defined data (we duplicate the marker here)
+#
+# Free/unused directory slot: all 32 bytes are 0x00 (type byte == 0x00)
+#
+
+import struct
+import sys
+
+ENTRY_SIZE = 32
+
+# exFAT directory entry type codes
+TYPE_FILE = 0x85
+TYPE_STREAM = 0xC0
+TYPE_FILENAME = 0xC1
+TYPE_VENDOR_EXT = 0xE0
+TYPE_FREE = 0x00
+
+# Offsets within specific entry types
+FILE_NUM_EXT_OFF = 1 # byte offset of num_ext in file entry
+FILE_CHECKSUM_OFF = 2 # byte offset of checksum in file entry
+STREAM_NAME_LEN_OFF = 3 # byte offset of name_len in stream entry
+FILENAME_CHARS_OFF = 2 # byte offset of first char in filename entry
+CHARS_PER_NAME_ENTRY = 15 # UTF-16LE characters per filename entry
+
+
+def find_entry_set(data, fname):
+ """Scan raw data for a FILE+STREAM+NAME entry set matching fname."""
+ pos = 0
+ while pos < len(data) - ENTRY_SIZE * 3:
+ if (data[pos] == TYPE_FILE and
+ data[pos + ENTRY_SIZE] == TYPE_STREAM and
+ data[pos + ENTRY_SIZE * 2] == TYPE_FILENAME):
+ name_len = data[pos + ENTRY_SIZE + STREAM_NAME_LEN_OFF]
+ num_name_entries = (name_len + CHARS_PER_NAME_ENTRY - 1) // \
+ CHARS_PER_NAME_ENTRY
+ chars = []
+ for ne in range(num_name_entries):
+ ne_off = pos + ENTRY_SIZE * (2 + ne)
+ for c in range(CHARS_PER_NAME_ENTRY):
+ if len(chars) >= name_len:
+ break
+ ch = struct.unpack_from('<H', data,
+ ne_off + FILENAME_CHARS_OFF +
+ c * 2)[0]
+ chars.append(chr(ch))
+ if ''.join(chars) == fname:
+ return pos
+ pos += ENTRY_SIZE
+ return -1
+
+
+def build_vendor_ext(marker_bytes, index):
+ """Build a single vendor_ext directory entry with marker payload."""
+ entry = bytearray(ENTRY_SIZE)
+ entry[0] = TYPE_VENDOR_EXT
+ tag = marker_bytes + struct.pack('B', index)
+ # Store marker in both the GUID field (bytes 2-15) and
+ # vendor-defined field (bytes 18-31)
+ entry[2:2 + min(len(tag), 14)] = tag[:14]
+ entry[18:18 + min(len(tag), 14)] = tag[:14]
+ return entry
+
+
+def update_checksum(data, file_off, num_ext):
+ """Recompute entry set checksum (skip bytes 2-3 of file entry)."""
+ es_len = ENTRY_SIZE * (1 + num_ext)
+ es_data = data[file_off:file_off + es_len]
+ chksum = 0
+ for i in range(len(es_data)):
+ if i == FILE_CHECKSUM_OFF or i == FILE_CHECKSUM_OFF + 1:
+ continue
+ chksum = (((chksum << 15) | (chksum >> 1)) + es_data[i]) & 0xFFFF
+ return chksum
+
+
+def main():
+ if len(sys.argv) < 4:
+ print("Usage: %s <device> <marker> <filename> [count]" % sys.argv[0],
+ file=sys.stderr)
+ sys.exit(1)
+
+ dev, marker_str, fname = sys.argv[1], sys.argv[2], sys.argv[3]
+ count = int(sys.argv[4]) if len(sys.argv) > 4 else 1
+ marker = marker_str.encode('ascii')
+
+ with open(dev, 'r+b') as f:
+ data = bytearray(f.read())
+
+ file_off = find_entry_set(data, fname)
+ if file_off < 0:
+ print("ERROR: could not find file '%s'" % fname, file=sys.stderr)
+ sys.exit(1)
+
+ num_ext = data[file_off + FILE_NUM_EXT_OFF]
+ es_end = file_off + ENTRY_SIZE * (1 + num_ext)
+
+ # Verify free slots exist after the entry set
+ for i in range(count):
+ slot = es_end + i * ENTRY_SIZE
+ if slot + ENTRY_SIZE > len(data) or data[slot] != TYPE_FREE:
+ print("ERROR: no free slot at offset %d for entry %d" %
+ (slot, i), file=sys.stderr)
+ sys.exit(1)
+
+ # Write vendor_ext entries into the free slots
+ for i in range(count):
+ slot = es_end + i * ENTRY_SIZE
+ entry = build_vendor_ext(marker, i)
+ data[slot:slot + ENTRY_SIZE] = entry
+
+ # Update num_ext in the file entry and recompute checksum
+ num_ext += count
+ data[file_off + FILE_NUM_EXT_OFF] = num_ext
+
+ chksum = update_checksum(data, file_off, num_ext)
+ struct.pack_into('<H', data, file_off + FILE_CHECKSUM_OFF, chksum)
+
+ with open(dev, 'r+b') as f:
+ f.write(data)
+
+ print("Injected %d vendor_ext entries for '%s' at offset %d, num_ext=%d" %
+ (count, fname, es_end, num_ext))
+
+
+if __name__ == '__main__':
+ main()
diff --git a/src/exfat_verify_vendor_ext.py b/src/exfat_verify_vendor_ext.py
new file mode 100755
index 00000000..2d7eb048
--- /dev/null
+++ b/src/exfat_verify_vendor_ext.py
@@ -0,0 +1,62 @@
+#!/usr/bin/python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Verify that vendor extension (0xE0) benign secondary entries with a
+# given marker are present in an exFAT filesystem image or block device.
+#
+# Usage: exfat_verify_vendor_ext.py <device> <marker> [count]
+#
+# Scans for a live (non-deleted) FILE entry set containing <count>
+# (default 1) vendor_ext entries with <marker>. Prints "PASS" or "FAIL".
+#
+# See exfat_inject_vendor_ext.py for the on-disk layout description.
+
+import sys
+
+ENTRY_SIZE = 32
+
+# exFAT directory entry type codes
+TYPE_FILE = 0x85
+TYPE_VENDOR_EXT = 0xE0
+
+# Offsets within the file entry
+FILE_NUM_EXT_OFF = 1
+
+
+def main():
+ if len(sys.argv) < 3:
+ print("Usage: %s <device> <marker> [count]" % sys.argv[0],
+ file=sys.stderr)
+ sys.exit(1)
+
+ dev, marker_str = sys.argv[1], sys.argv[2]
+ expected = int(sys.argv[3]) if len(sys.argv) > 3 else 1
+ marker = marker_str.encode('ascii')
+
+ with open(dev, 'rb') as f:
+ data = f.read()
+
+ # Walk directory entries looking for a FILE entry set that contains
+ # the expected number of vendor_ext entries with our marker.
+ for i in range(0, len(data) - ENTRY_SIZE, ENTRY_SIZE):
+ if data[i] != TYPE_FILE:
+ continue
+ num_ext = data[i + FILE_NUM_EXT_OFF]
+ found = 0
+ for j in range(1, num_ext + 1):
+ off = i + j * ENTRY_SIZE
+ if off + ENTRY_SIZE > len(data):
+ break
+ if data[off] == TYPE_VENDOR_EXT and \
+ marker in data[off:off + ENTRY_SIZE]:
+ found += 1
+ if found >= expected:
+ print("PASS")
+ sys.exit(0)
+
+ print("FAIL")
+ sys.exit(1)
+
+
+if __name__ == '__main__':
+ main()
diff --git a/tests/exfat/001 b/tests/exfat/001
new file mode 100755
index 00000000..858e9750
--- /dev/null
+++ b/tests/exfat/001
@@ -0,0 +1,171 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 Rochan Avlur. All Rights Reserved.
+#
+# FS QA Test No. exfat/001
+#
+# Verify that rename and cross-directory move do not destroy
+# unrecognized benign secondary directory entries. exFAT spec section 8.2
+# requires implementations to preserve benign secondary entries they
+# do not recognize.
+#
+# Regression test for kernel commit 8258ef28001a
+# ("exfat: handle unreconized benign secondary entries") which added
+# cluster freeing for benign secondary entries inside
+# exfat_remove_entries(), but that function is also called by the
+# rename and move paths where freeing is incorrect.
+#
+. ./common/preamble
+_begin_fstest auto quick
+
+# Override the default cleanup function.
+_cleanup()
+{
+ cd /
+ _unmount $loop_mnt 2>/dev/null
+ [ -n "$loop_dev" ] && _destroy_loop_device $loop_dev
+ rm -rf $loop_mnt $img_file $tmp.*
+}
+
+_fixed_by_kernel_commit 942296784b2a \
+ "exfat: preserve benign secondary entries during rename and move"
+
+_require_test
+_require_loop
+_require_command "$PYTHON3_PROG" python3
+
+img_file=$TEST_DIR/$seq.exfat.img
+loop_mnt=$TEST_DIR/$seq.mnt
+loop_dev=""
+
+INJECT=$here/src/exfat_inject_vendor_ext.py
+VERIFY=$here/src/exfat_verify_vendor_ext.py
+MARKER="XFST_BENIGN_01"
+
+create_exfat_image()
+{
+ rm -f $img_file
+ truncate -s 10M $img_file
+ loop_dev=$(_create_loop_device $img_file)
+ _mkfs_dev $loop_dev >> $seqres.full 2>&1
+ mkdir -p $loop_mnt
+}
+
+mount_image()
+{
+ _mount $loop_dev $loop_mnt
+}
+
+unmount_image()
+{
+ _unmount $loop_mnt
+}
+
+teardown_image()
+{
+ _unmount $loop_mnt 2>/dev/null
+ _destroy_loop_device $loop_dev
+ loop_dev=""
+}
+
+verify_benign_preserved()
+{
+ local label="$1"
+ local count="${2:-1}"
+
+ result=$($PYTHON3_PROG $VERIFY $loop_dev "$MARKER" "$count" \
+ 2>>$seqres.full)
+ if [ "$result" = "PASS" ]; then
+ echo "PASS: benign secondary entries preserved after $label"
+ else
+ echo "FAIL: benign secondary entries destroyed by $label"
+ fi
+}
+
+# Test 1: rename to longer name (entry set must be relocated)
+create_exfat_image
+mount_image
+echo "payload" > $loop_mnt/a
+unmount_image
+
+$PYTHON3_PROG $INJECT $loop_dev "$MARKER" a \
+ >> $seqres.full 2>&1 || _fail "inject failed for test 1"
+
+mount_image
+mv $loop_mnt/a "$loop_mnt/a_long_name_to_force_entry_set_relocation"
+unmount_image
+
+verify_benign_preserved "rename to longer name"
+teardown_image
+
+# Test 2: cross-directory move
+create_exfat_image
+mount_image
+echo "payload" > $loop_mnt/b
+unmount_image
+
+$PYTHON3_PROG $INJECT $loop_dev "$MARKER" b \
+ >> $seqres.full 2>&1 || _fail "inject failed for test 2"
+
+mount_image
+mkdir $loop_mnt/subdir
+mv $loop_mnt/b $loop_mnt/subdir/b
+unmount_image
+
+verify_benign_preserved "cross-directory move"
+teardown_image
+
+# Test 3: rename to shorter name (entry set is updated in place)
+create_exfat_image
+mount_image
+echo "payload" > "$loop_mnt/a_long_name_to_force_multiple_name_entries"
+unmount_image
+
+$PYTHON3_PROG $INJECT $loop_dev "$MARKER" \
+ a_long_name_to_force_multiple_name_entries \
+ >> $seqres.full 2>&1 || _fail "inject failed for test 3"
+
+mount_image
+mv "$loop_mnt/a_long_name_to_force_multiple_name_entries" $loop_mnt/c
+unmount_image
+
+verify_benign_preserved "rename to shorter name"
+teardown_image
+
+# Test 4: rename overwriting an existing file (source's benign entries
+# must survive even though the target's entries are deleted)
+create_exfat_image
+mount_image
+echo "target" > $loop_mnt/dst
+echo "source" > $loop_mnt/src
+unmount_image
+
+$PYTHON3_PROG $INJECT $loop_dev "$MARKER" src \
+ >> $seqres.full 2>&1 || _fail "inject failed for test 4 (src)"
+
+mount_image
+mv $loop_mnt/src $loop_mnt/dst
+unmount_image
+
+verify_benign_preserved "rename overwriting existing file"
+teardown_image
+
+# Test 5: multiple benign entries (verifies all are copied, not just one)
+create_exfat_image
+mount_image
+echo "payload" > $loop_mnt/m
+unmount_image
+
+$PYTHON3_PROG $INJECT $loop_dev "$MARKER" m 3 \
+ >> $seqres.full 2>&1 || _fail "inject failed for test 5"
+
+mount_image
+mv $loop_mnt/m "$loop_mnt/m_longer_name_for_relocation"
+unmount_image
+
+verify_benign_preserved "rename with multiple benign entries" 3
+teardown_image
+
+# success, all done
+status=0
+exit
diff --git a/tests/exfat/001.out b/tests/exfat/001.out
new file mode 100644
index 00000000..f82ea010
--- /dev/null
+++ b/tests/exfat/001.out
@@ -0,0 +1,6 @@
+QA output created by 001
+PASS: benign secondary entries preserved after rename to longer name
+PASS: benign secondary entries preserved after cross-directory move
+PASS: benign secondary entries preserved after rename to shorter name
+PASS: benign secondary entries preserved after rename overwriting existing file
+PASS: benign secondary entries preserved after rename with multiple benign entries
diff --git a/tests/exfat/Makefile b/tests/exfat/Makefile
new file mode 100644
index 00000000..9322f797
--- /dev/null
+++ b/tests/exfat/Makefile
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 Rochan Avlur. All Rights Reserved.
+
+TOPDIR = ../..
+include $(TOPDIR)/include/builddefs
+include $(TOPDIR)/include/buildgrouplist
+
+EXFAT_DIR = exfat
+TARGET_DIR = $(PKG_LIB_DIR)/$(TESTS_DIR)/$(EXFAT_DIR)
+DIRT = group.list
+
+default: $(DIRT)
+
+include $(BUILDRULES)
+
+install: default
+ $(INSTALL) -m 755 -d $(TARGET_DIR)
+ $(INSTALL) -m 755 $(TESTS) $(TARGET_DIR)
+ $(INSTALL) -m 644 group.list $(TARGET_DIR)
+ $(INSTALL) -m 644 $(OUTFILES) $(TARGET_DIR)
+
+# Nothing.
+install-dev install-lib:
--
2.45.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] exfat/001: test that rename and move preserve benign secondary entries
2026-07-23 4:11 [PATCH] exfat/001: test that rename and move preserve benign secondary entries Rochan Avlur
@ 2026-08-12 18:06 ` Zorro Lang
0 siblings, 0 replies; 2+ messages in thread
From: Zorro Lang @ 2026-08-12 18:06 UTC (permalink / raw)
To: Rochan Avlur; +Cc: fstests, linkinjeon, Yuezhang.Mo
On Wed, Jul 22, 2026 at 09:11:55PM -0700, Rochan Avlur wrote:
> Verify that unrecognized benign secondary directory entries (such as
> vendor extensions) survive same-directory rename, cross-directory move,
> in-place rename to a shorter name, rename overwriting an existing file,
> and operations on files with multiple benign entries.
>
> exFAT spec section 8.2 [1] requires implementations to preserve benign
> secondary entries they do not recognize. This is a regression test for
> kernel commit 8258ef28001a ("exfat: handle unreconized benign secondary
> entries") which incorrectly freed benign entry clusters in the rename
> and move paths.
>
> [1]: https://learn.microsoft.com/en-us/windows/win32/fileio/exfat-specification#8-implementation-notes
>
> Signed-off-by: Rochan Avlur <rochan.avlur@gmail.com>
> ---
> src/Makefile | 3 +-
> src/exfat_inject_vendor_ext.py | 155 ++++++++++++++++++++++++++++++
> src/exfat_verify_vendor_ext.py | 62 ++++++++++++
> tests/exfat/001 | 171 +++++++++++++++++++++++++++++++++
> tests/exfat/001.out | 6 ++
> tests/exfat/Makefile | 23 +++++
> 6 files changed, 419 insertions(+), 1 deletion(-)
> create mode 100755 src/exfat_inject_vendor_ext.py
> create mode 100755 src/exfat_verify_vendor_ext.py
> create mode 100755 tests/exfat/001
> create mode 100644 tests/exfat/001.out
> create mode 100644 tests/exfat/Makefile
>
> diff --git a/src/Makefile b/src/Makefile
> index 31ac43b2..a42cf96f 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -40,7 +40,8 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
>
> EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
> btrfs_crc32c_forged_name.py popdir.pl popattr.py \
> - soak_duration.awk parse-dev-tree.awk parse-free-space.py
> + soak_duration.awk parse-dev-tree.awk parse-free-space.py \
> + exfat_inject_vendor_ext.py exfat_verify_vendor_ext.py
>
> SUBDIRS = log-writes perf
>
> diff --git a/src/exfat_inject_vendor_ext.py b/src/exfat_inject_vendor_ext.py
> new file mode 100755
> index 00000000..81350da8
> --- /dev/null
> +++ b/src/exfat_inject_vendor_ext.py
> @@ -0,0 +1,155 @@
> +#!/usr/bin/python3
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Inject vendor extension (0xE0) benign secondary entries into an exFAT
> +# directory entry set on an unmounted filesystem image or block device.
> +#
> +# Usage: exfat_inject_vendor_ext.py <device> <marker> <filename> [count]
> +#
> +# Adds <count> (default 1) vendor_ext entries carrying <marker> into the
> +# entry set of <filename>. The marker is stored in the custom-defined
> +# area so it can be verified after kernel operations.
> +#
> +# exFAT on-disk directory entry layout (each entry is 32 bytes):
> +#
> +# Entry set for a file:
> +# [0] File entry (type 0x85)
> +# byte 1: num_ext (number of secondary entries following)
> +# bytes 2-3: entry set checksum (covers all entries, skipping these bytes)
> +# [1] Stream extension (type 0xC0)
> +# byte 3: name_len (filename length in Unicode characters)
> +# bytes 4-7: name_hash
> +# [2..N] Filename entries (type 0xC1, each holds up to 15 UTF-16LE chars)
> +# bytes 2-31: 15 UTF-16LE characters
> +# [N+1..] Benign secondary entries (type 0xA0-0xFF, e.g. vendor_ext 0xE0)
> +# Implementations MUST preserve these even if unrecognized (spec s8.2)
> +#
> +# Vendor extension entry (type 0xE0):
> +# byte 0: 0xE0 (entry type)
> +# bytes 2-15: vendor GUID (we store our marker here)
> +# bytes 18-31: vendor-defined data (we duplicate the marker here)
> +#
> +# Free/unused directory slot: all 32 bytes are 0x00 (type byte == 0x00)
> +#
> +
> +import struct
> +import sys
> +
> +ENTRY_SIZE = 32
> +
> +# exFAT directory entry type codes
> +TYPE_FILE = 0x85
> +TYPE_STREAM = 0xC0
> +TYPE_FILENAME = 0xC1
> +TYPE_VENDOR_EXT = 0xE0
> +TYPE_FREE = 0x00
> +
> +# Offsets within specific entry types
> +FILE_NUM_EXT_OFF = 1 # byte offset of num_ext in file entry
> +FILE_CHECKSUM_OFF = 2 # byte offset of checksum in file entry
> +STREAM_NAME_LEN_OFF = 3 # byte offset of name_len in stream entry
> +FILENAME_CHARS_OFF = 2 # byte offset of first char in filename entry
> +CHARS_PER_NAME_ENTRY = 15 # UTF-16LE characters per filename entry
> +
> +
> +def find_entry_set(data, fname):
> + """Scan raw data for a FILE+STREAM+NAME entry set matching fname."""
> + pos = 0
> + while pos < len(data) - ENTRY_SIZE * 3:
> + if (data[pos] == TYPE_FILE and
> + data[pos + ENTRY_SIZE] == TYPE_STREAM and
> + data[pos + ENTRY_SIZE * 2] == TYPE_FILENAME):
> + name_len = data[pos + ENTRY_SIZE + STREAM_NAME_LEN_OFF]
> + num_name_entries = (name_len + CHARS_PER_NAME_ENTRY - 1) // \
> + CHARS_PER_NAME_ENTRY
> + chars = []
> + for ne in range(num_name_entries):
> + ne_off = pos + ENTRY_SIZE * (2 + ne)
> + for c in range(CHARS_PER_NAME_ENTRY):
> + if len(chars) >= name_len:
> + break
> + ch = struct.unpack_from('<H', data,
> + ne_off + FILENAME_CHARS_OFF +
> + c * 2)[0]
> + chars.append(chr(ch))
> + if ''.join(chars) == fname:
> + return pos
> + pos += ENTRY_SIZE
> + return -1
> +
> +
> +def build_vendor_ext(marker_bytes, index):
> + """Build a single vendor_ext directory entry with marker payload."""
> + entry = bytearray(ENTRY_SIZE)
> + entry[0] = TYPE_VENDOR_EXT
> + tag = marker_bytes + struct.pack('B', index)
> + # Store marker in both the GUID field (bytes 2-15) and
> + # vendor-defined field (bytes 18-31)
> + entry[2:2 + min(len(tag), 14)] = tag[:14]
> + entry[18:18 + min(len(tag), 14)] = tag[:14]
> + return entry
> +
> +
> +def update_checksum(data, file_off, num_ext):
> + """Recompute entry set checksum (skip bytes 2-3 of file entry)."""
> + es_len = ENTRY_SIZE * (1 + num_ext)
> + es_data = data[file_off:file_off + es_len]
> + chksum = 0
> + for i in range(len(es_data)):
> + if i == FILE_CHECKSUM_OFF or i == FILE_CHECKSUM_OFF + 1:
> + continue
> + chksum = (((chksum << 15) | (chksum >> 1)) + es_data[i]) & 0xFFFF
> + return chksum
> +
> +
> +def main():
> + if len(sys.argv) < 4:
> + print("Usage: %s <device> <marker> <filename> [count]" % sys.argv[0],
> + file=sys.stderr)
> + sys.exit(1)
> +
> + dev, marker_str, fname = sys.argv[1], sys.argv[2], sys.argv[3]
> + count = int(sys.argv[4]) if len(sys.argv) > 4 else 1
> + marker = marker_str.encode('ascii')
> +
> + with open(dev, 'r+b') as f:
> + data = bytearray(f.read())
It looks like exfat needs a tool like xfs_db or debugfs :) Reading the entire
disk into memory at once only works for tiny filesystem sizes, that is why
you chose a loop device over SCRATCH_DEV as the test device below.
For this specific exfat test case, I think this patch's logic is acceptable,
especially since it covers a known regression bug. If there are no further
review comments from exfat developers, I will merge this patch. More exfat
test coverage is always welcome.
Reviewed-by: Zorro Lang <zlang@kernel.org>
> +
> + file_off = find_entry_set(data, fname)
> + if file_off < 0:
> + print("ERROR: could not find file '%s'" % fname, file=sys.stderr)
> + sys.exit(1)
> +
> + num_ext = data[file_off + FILE_NUM_EXT_OFF]
> + es_end = file_off + ENTRY_SIZE * (1 + num_ext)
> +
> + # Verify free slots exist after the entry set
> + for i in range(count):
> + slot = es_end + i * ENTRY_SIZE
> + if slot + ENTRY_SIZE > len(data) or data[slot] != TYPE_FREE:
> + print("ERROR: no free slot at offset %d for entry %d" %
> + (slot, i), file=sys.stderr)
> + sys.exit(1)
> +
> + # Write vendor_ext entries into the free slots
> + for i in range(count):
> + slot = es_end + i * ENTRY_SIZE
> + entry = build_vendor_ext(marker, i)
> + data[slot:slot + ENTRY_SIZE] = entry
> +
> + # Update num_ext in the file entry and recompute checksum
> + num_ext += count
> + data[file_off + FILE_NUM_EXT_OFF] = num_ext
> +
> + chksum = update_checksum(data, file_off, num_ext)
> + struct.pack_into('<H', data, file_off + FILE_CHECKSUM_OFF, chksum)
> +
> + with open(dev, 'r+b') as f:
> + f.write(data)
> +
> + print("Injected %d vendor_ext entries for '%s' at offset %d, num_ext=%d" %
> + (count, fname, es_end, num_ext))
> +
> +
> +if __name__ == '__main__':
> + main()
> diff --git a/src/exfat_verify_vendor_ext.py b/src/exfat_verify_vendor_ext.py
> new file mode 100755
> index 00000000..2d7eb048
> --- /dev/null
> +++ b/src/exfat_verify_vendor_ext.py
> @@ -0,0 +1,62 @@
> +#!/usr/bin/python3
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Verify that vendor extension (0xE0) benign secondary entries with a
> +# given marker are present in an exFAT filesystem image or block device.
> +#
> +# Usage: exfat_verify_vendor_ext.py <device> <marker> [count]
> +#
> +# Scans for a live (non-deleted) FILE entry set containing <count>
> +# (default 1) vendor_ext entries with <marker>. Prints "PASS" or "FAIL".
> +#
> +# See exfat_inject_vendor_ext.py for the on-disk layout description.
> +
> +import sys
> +
> +ENTRY_SIZE = 32
> +
> +# exFAT directory entry type codes
> +TYPE_FILE = 0x85
> +TYPE_VENDOR_EXT = 0xE0
> +
> +# Offsets within the file entry
> +FILE_NUM_EXT_OFF = 1
> +
> +
> +def main():
> + if len(sys.argv) < 3:
> + print("Usage: %s <device> <marker> [count]" % sys.argv[0],
> + file=sys.stderr)
> + sys.exit(1)
> +
> + dev, marker_str = sys.argv[1], sys.argv[2]
> + expected = int(sys.argv[3]) if len(sys.argv) > 3 else 1
> + marker = marker_str.encode('ascii')
> +
> + with open(dev, 'rb') as f:
> + data = f.read()
> +
> + # Walk directory entries looking for a FILE entry set that contains
> + # the expected number of vendor_ext entries with our marker.
> + for i in range(0, len(data) - ENTRY_SIZE, ENTRY_SIZE):
> + if data[i] != TYPE_FILE:
> + continue
> + num_ext = data[i + FILE_NUM_EXT_OFF]
> + found = 0
> + for j in range(1, num_ext + 1):
> + off = i + j * ENTRY_SIZE
> + if off + ENTRY_SIZE > len(data):
> + break
> + if data[off] == TYPE_VENDOR_EXT and \
> + marker in data[off:off + ENTRY_SIZE]:
> + found += 1
> + if found >= expected:
> + print("PASS")
> + sys.exit(0)
> +
> + print("FAIL")
> + sys.exit(1)
> +
> +
> +if __name__ == '__main__':
> + main()
> diff --git a/tests/exfat/001 b/tests/exfat/001
> new file mode 100755
> index 00000000..858e9750
> --- /dev/null
> +++ b/tests/exfat/001
> @@ -0,0 +1,171 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 Rochan Avlur. All Rights Reserved.
> +#
> +# FS QA Test No. exfat/001
> +#
> +# Verify that rename and cross-directory move do not destroy
> +# unrecognized benign secondary directory entries. exFAT spec section 8.2
> +# requires implementations to preserve benign secondary entries they
> +# do not recognize.
> +#
> +# Regression test for kernel commit 8258ef28001a
> +# ("exfat: handle unreconized benign secondary entries") which added
> +# cluster freeing for benign secondary entries inside
> +# exfat_remove_entries(), but that function is also called by the
> +# rename and move paths where freeing is incorrect.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick
> +
> +# Override the default cleanup function.
> +_cleanup()
> +{
> + cd /
> + _unmount $loop_mnt 2>/dev/null
> + [ -n "$loop_dev" ] && _destroy_loop_device $loop_dev
> + rm -rf $loop_mnt $img_file $tmp.*
> +}
> +
> +_fixed_by_kernel_commit 942296784b2a \
> + "exfat: preserve benign secondary entries during rename and move"
> +
> +_require_test
> +_require_loop
> +_require_command "$PYTHON3_PROG" python3
> +
> +img_file=$TEST_DIR/$seq.exfat.img
> +loop_mnt=$TEST_DIR/$seq.mnt
> +loop_dev=""
> +
> +INJECT=$here/src/exfat_inject_vendor_ext.py
> +VERIFY=$here/src/exfat_verify_vendor_ext.py
> +MARKER="XFST_BENIGN_01"
> +
> +create_exfat_image()
> +{
> + rm -f $img_file
> + truncate -s 10M $img_file
> + loop_dev=$(_create_loop_device $img_file)
> + _mkfs_dev $loop_dev >> $seqres.full 2>&1
> + mkdir -p $loop_mnt
> +}
> +
> +mount_image()
> +{
> + _mount $loop_dev $loop_mnt
> +}
> +
> +unmount_image()
> +{
> + _unmount $loop_mnt
> +}
> +
> +teardown_image()
> +{
> + _unmount $loop_mnt 2>/dev/null
> + _destroy_loop_device $loop_dev
> + loop_dev=""
> +}
> +
> +verify_benign_preserved()
> +{
> + local label="$1"
> + local count="${2:-1}"
> +
> + result=$($PYTHON3_PROG $VERIFY $loop_dev "$MARKER" "$count" \
> + 2>>$seqres.full)
> + if [ "$result" = "PASS" ]; then
> + echo "PASS: benign secondary entries preserved after $label"
> + else
> + echo "FAIL: benign secondary entries destroyed by $label"
> + fi
> +}
> +
> +# Test 1: rename to longer name (entry set must be relocated)
> +create_exfat_image
> +mount_image
> +echo "payload" > $loop_mnt/a
> +unmount_image
> +
> +$PYTHON3_PROG $INJECT $loop_dev "$MARKER" a \
> + >> $seqres.full 2>&1 || _fail "inject failed for test 1"
> +
> +mount_image
> +mv $loop_mnt/a "$loop_mnt/a_long_name_to_force_entry_set_relocation"
> +unmount_image
> +
> +verify_benign_preserved "rename to longer name"
> +teardown_image
> +
> +# Test 2: cross-directory move
> +create_exfat_image
> +mount_image
> +echo "payload" > $loop_mnt/b
> +unmount_image
> +
> +$PYTHON3_PROG $INJECT $loop_dev "$MARKER" b \
> + >> $seqres.full 2>&1 || _fail "inject failed for test 2"
> +
> +mount_image
> +mkdir $loop_mnt/subdir
> +mv $loop_mnt/b $loop_mnt/subdir/b
> +unmount_image
> +
> +verify_benign_preserved "cross-directory move"
> +teardown_image
> +
> +# Test 3: rename to shorter name (entry set is updated in place)
> +create_exfat_image
> +mount_image
> +echo "payload" > "$loop_mnt/a_long_name_to_force_multiple_name_entries"
> +unmount_image
> +
> +$PYTHON3_PROG $INJECT $loop_dev "$MARKER" \
> + a_long_name_to_force_multiple_name_entries \
> + >> $seqres.full 2>&1 || _fail "inject failed for test 3"
> +
> +mount_image
> +mv "$loop_mnt/a_long_name_to_force_multiple_name_entries" $loop_mnt/c
> +unmount_image
> +
> +verify_benign_preserved "rename to shorter name"
> +teardown_image
> +
> +# Test 4: rename overwriting an existing file (source's benign entries
> +# must survive even though the target's entries are deleted)
> +create_exfat_image
> +mount_image
> +echo "target" > $loop_mnt/dst
> +echo "source" > $loop_mnt/src
> +unmount_image
> +
> +$PYTHON3_PROG $INJECT $loop_dev "$MARKER" src \
> + >> $seqres.full 2>&1 || _fail "inject failed for test 4 (src)"
> +
> +mount_image
> +mv $loop_mnt/src $loop_mnt/dst
> +unmount_image
> +
> +verify_benign_preserved "rename overwriting existing file"
> +teardown_image
> +
> +# Test 5: multiple benign entries (verifies all are copied, not just one)
> +create_exfat_image
> +mount_image
> +echo "payload" > $loop_mnt/m
> +unmount_image
> +
> +$PYTHON3_PROG $INJECT $loop_dev "$MARKER" m 3 \
> + >> $seqres.full 2>&1 || _fail "inject failed for test 5"
> +
> +mount_image
> +mv $loop_mnt/m "$loop_mnt/m_longer_name_for_relocation"
> +unmount_image
> +
> +verify_benign_preserved "rename with multiple benign entries" 3
> +teardown_image
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/exfat/001.out b/tests/exfat/001.out
> new file mode 100644
> index 00000000..f82ea010
> --- /dev/null
> +++ b/tests/exfat/001.out
> @@ -0,0 +1,6 @@
> +QA output created by 001
> +PASS: benign secondary entries preserved after rename to longer name
> +PASS: benign secondary entries preserved after cross-directory move
> +PASS: benign secondary entries preserved after rename to shorter name
> +PASS: benign secondary entries preserved after rename overwriting existing file
> +PASS: benign secondary entries preserved after rename with multiple benign entries
> diff --git a/tests/exfat/Makefile b/tests/exfat/Makefile
> new file mode 100644
> index 00000000..9322f797
> --- /dev/null
> +++ b/tests/exfat/Makefile
> @@ -0,0 +1,23 @@
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 Rochan Avlur. All Rights Reserved.
> +
> +TOPDIR = ../..
> +include $(TOPDIR)/include/builddefs
> +include $(TOPDIR)/include/buildgrouplist
> +
> +EXFAT_DIR = exfat
> +TARGET_DIR = $(PKG_LIB_DIR)/$(TESTS_DIR)/$(EXFAT_DIR)
> +DIRT = group.list
> +
> +default: $(DIRT)
> +
> +include $(BUILDRULES)
> +
> +install: default
> + $(INSTALL) -m 755 -d $(TARGET_DIR)
> + $(INSTALL) -m 755 $(TESTS) $(TARGET_DIR)
> + $(INSTALL) -m 644 group.list $(TARGET_DIR)
> + $(INSTALL) -m 644 $(OUTFILES) $(TARGET_DIR)
> +
> +# Nothing.
> +install-dev install-lib:
> --
> 2.45.2
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-07-23 4:11 [PATCH] exfat/001: test that rename and move preserve benign secondary entries Rochan Avlur
2026-08-12 18:06 ` Zorro Lang
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