| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <2c241ea2ede39914d29aa59cd06acfc951aed160.1754833177.git.ojaswin@linux.ibm.com>
Date: Sun, 10 Aug 2025 19:12:02 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Zorro Lang <zlang@...hat.com>, fstests@...r.kernel.org
Cc: Ritesh Harjani <ritesh.list@...il.com>, djwong@...nel.org,
john.g.garry@...cle.com, tytso@....edu, linux-xfs@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: [PATCH v4 11/11] ext4: Atomic write test for extent split across leaf nodes
In ext4, even if an allocated range is physically and logically
contiguous, it can still be split into 2 extents. This is because ext4
does not merge extents across leaf nodes. This is an issue for atomic
writes since even for a continuous extent the map block could (in rare
cases) return a shorter map, hence tearning the write. This test creates
such a file and ensures that the atomic write handles this case
correctly
Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
tests/ext4/063 | 129 +++++++++++++++++++++++++++++++++++++++++++++
tests/ext4/063.out | 2 +
2 files changed, 131 insertions(+)
create mode 100755 tests/ext4/063
create mode 100644 tests/ext4/063.out
diff --git a/tests/ext4/063 b/tests/ext4/063
new file mode 100755
index 00000000..40867acb
--- /dev/null
+++ b/tests/ext4/063
@@ -0,0 +1,129 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2025 IBM Corporation. All Rights Reserved.
+#
+# In ext4, even if an allocated range is physically and logically contiguous,
+# it can still be split into 2 extents. This is because ext4 does not merge
+# extents across leaf nodes. This is an issue for atomic writes since even for
+# a continuous extent the map block could (in rare cases) return a shorter map,
+# hence tearning the write. This test creates such a file and ensures that the
+# atomic write handles this case correctly
+#
+. ./common/preamble
+. ./common/atomicwrites
+_begin_fstest auto atomicwrites
+
+_require_scratch_write_atomic_multi_fsblock
+_require_atomic_write_test_commands
+_require_command "$DEBUGFS_PROG" debugfs
+
+prep() {
+ local bs=`_get_block_size $SCRATCH_MNT`
+ local ex_hdr_bytes=12
+ local ex_entry_bytes=12
+ local entries_per_blk=$(( (bs - ex_hdr_bytes) / ex_entry_bytes ))
+
+ # fill the extent tree leaf with bs len extents at alternate offsets.
+ # The tree should look as follows
+ #
+ # +---------+---------+
+ # | index 1 | index 2 |
+ # +-----+---+-----+---+
+ # +------+ +-----------+
+ # | |
+ # +-------+-------+---+---------+ +-----+----+
+ # | ex 1 | ex 2 | | ex n | | ex n+1 |
+ # | off:0 | off:2 |...| off:678 | | off:680 |
+ # | len:1 | len:1 | | len:1 | | len:1 |
+ # +-------+-------+---+---------+ +----------+
+ #
+ for i in $(seq 0 $entries_per_blk)
+ do
+ $XFS_IO_PROG -fc "pwrite -b $bs $((i * 2 * bs)) $bs" $testfile > /dev/null
+ done
+ sync $testfile
+
+ echo >> $seqres.full
+ echo "Create file with extents spanning 2 leaves. Extents:">> $seqres.full
+ echo "...">> $seqres.full
+ $DEBUGFS_PROG -R "ex `basename $testfile`" $SCRATCH_DEV |& tail >> $seqres.full
+
+ # Now try to insert a new extent ex(new) between ex(n) and ex(n+1).
+ # Since this is a new FS the allocator would find continuous blocks
+ # such that ex(n) ex(new) ex(n+1) are physically(and logically)
+ # contiguous. However, since we dont merge extents across leaf we will
+ # end up with a tree as:
+ #
+ # +---------+---------+
+ # | index 1 | index 2 |
+ # +-----+---+-----+---+
+ # +------+ +------------+
+ # | |
+ # +-------+-------+---+---------+ +------+-----------+
+ # | ex 1 | ex 2 | | ex n | | ex n+1 (merged) |
+ # | off:0 | off:2 |...| off:678 | | off:679 |
+ # | len:1 | len:1 | | len:1 | | len:2 |
+ # +-------+-------+---+---------+ +------------------+
+ #
+ echo >> $seqres.full
+ torn_ex_offset=$((((entries_per_blk * 2) - 1) * bs))
+ $XFS_IO_PROG -c "pwrite $torn_ex_offset $bs" $testfile >> /dev/null
+ sync $testfile
+
+ echo >> $seqres.full
+ echo "Perform 1 block write at $torn_ex_offset to create torn extent. Extents:">> $seqres.full
+ echo "...">> $seqres.full
+ $DEBUGFS_PROG -R "ex `basename $testfile`" $SCRATCH_DEV |& tail >> $seqres.full
+
+ _scratch_cycle_mount
+}
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount >> $seqres.full
+
+testfile=$SCRATCH_MNT/testfile
+touch $testfile
+awu_max=$(_get_atomic_write_unit_max $testfile)
+
+echo >> $seqres.full
+echo "# Prepping the file" >> $seqres.full
+prep
+
+torn_aw_offset=$((torn_ex_offset - (torn_ex_offset % awu_max)))
+
+echo >> $seqres.full
+echo "# Performing atomic IO on the torn extent range. Command: " >> $seqres.full
+echo $XFS_IO_PROG -c "open -fsd $testfile" -c "pwrite -S 0x61 -DA -V1 -b $awu_max $torn_aw_offset $awu_max" >> $seqres.full
+$XFS_IO_PROG -c "open -fsd $testfile" -c "pwrite -S 0x61 -DA -V1 -b $awu_max $torn_aw_offset $awu_max" >> $seqres.full
+
+echo >> $seqres.full
+echo "Extent state after atomic write:">> $seqres.full
+echo "...">> $seqres.full
+$DEBUGFS_PROG -R "ex `basename $testfile`" $SCRATCH_DEV |& tail >> $seqres.full
+
+echo >> $seqres.full
+echo "# Checking data integrity" >> $seqres.full
+
+# create a dummy file with expected data
+$XFS_IO_PROG -fc "pwrite -S 0x61 -b $awu_max 0 $awu_max" $testfile.exp >> /dev/null
+expected_data=$(od -An -t x1 -j 0 -N $awu_max $testfile.exp)
+
+# We ensure that the data after atomic writes should match the expected data
+actual_data=$(od -An -t x1 -j $torn_aw_offset -N $awu_max $testfile)
+if [[ "$actual_data" != "$expected_data" ]]
+then
+ echo "Checksum match failed at off: $torn_aw_offset size: $awu_max"
+ echo
+ echo "Expected: "
+ echo "$expected_data"
+ echo
+ echo "Actual contents: "
+ echo "$actual_data"
+
+ _fail
+fi
+
+echo -n "Data verification at offset $torn_aw_offset suceeded!" >> $seqres.full
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/ext4/063.out b/tests/ext4/063.out
new file mode 100644
index 00000000..de35fc52
--- /dev/null
+++ b/tests/ext4/063.out
@@ -0,0 +1,2 @@
+QA output created by 063
+Silence is golden
--
2.49.0
Powered by blists - more mailing lists