KASAN: null-ptr-deref Write in fput

Status: upstream: reported C repro on 2026/08/08 19:56
Subsystems: ocfs2
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+5d4e96acd0febccb5e87@syzkaller.appspotmail.com
First crash: 4d20h, last: 4d12h
Cause bisection: failed (error log, bisect log)
  
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ID Workflow Result Correct Bug Created Started Finished Revision
f22404c7 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: null-ptr-deref Write in fput 2026/08/09 08:16 2026/08/09 08:16 2026/08/09 08:58 5d63f80b
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Title Replies (including bot) Last reply
[syzbot] [ocfs2?] KASAN: null-ptr-deref Write in fput 0 (1) 2026/08/08 19:56

Sample crash report:
(syz-executor157,5664,1):o2hb_bio_end_io:499 ERROR: IO Error 10
(syz-executor157,5664,1):o2hb_region_dev_store:1850 ERROR: status = -5
==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: null-ptr-deref in atomic_long_dec_return include/linux/atomic/atomic-instrumented.h:3766 [inline]
BUG: KASAN: null-ptr-deref in file_ref_put include/linux/file_ref.h:157 [inline]
BUG: KASAN: null-ptr-deref in fput+0x2e/0x100 fs/file_table.c:588
Write of size 8 at addr 0000000000000158 by task syz-executor157/5664

CPU: 1 UID: 0 PID: 5664 Comm: syz-executor157 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:186 [inline]
 kasan_check_range+0x10f/0x1e0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_long_dec_return include/linux/atomic/atomic-instrumented.h:3766 [inline]
 file_ref_put include/linux/file_ref.h:157 [inline]
 fput+0x2e/0x100 fs/file_table.c:588
 o2hb_region_dev_store+0x1230/0x1bc0 fs/ocfs2/cluster/heartbeat.c:1935
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd8eccb5ab9
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc7d881e78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000200000000540 RCX: 00007fd8eccb5ab9
RDX: 0000000000000001 RSI: 00002000000005c0 RDI: 0000000000000004
RBP: 0030706f6f6c2f2e R08: 0000000000000009 R09: 0000000000000009
R10: 0000000000000009 R11: 0000000000000246 R12: 000000000001009b
R13: 00007ffc7d881e8c R14: 00007ffc7d881ea0 R15: 0000200000000008
 </TASK>
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/05 00:44 upstream 848acc8ffe1b d4abbeac .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: null-ptr-deref Write in fput
2026/08/04 16:29 upstream 848acc8ffe1b d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: null-ptr-deref Write in fput
2026/08/04 16:29 upstream 848acc8ffe1b d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: null-ptr-deref Write in fput
* Struck through repros no longer work on HEAD.