KASAN: use-after-free Read in ignore_event

Status: moderation: reported on 2026/08/05 00:23
Subsystems: trace
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+3d4924f21a3902be1be4@syzkaller.appspotmail.com
First crash: 7d06h, last: 7d06h
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ID Workflow Result Correct Bug Created Started Finished Revision
ffc309e2 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: use-after-free Read in ignore_event 2026/08/02 01:44 2026/08/02 01:44 2026/08/02 02:21 e611ffe1

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ignore_event+0x83e/0xaa0 kernel/trace/trace.c:2526
Read of size 2 at addr ffff88804705a1ac by task syz.6.1383/11771

CPU: 0 UID: 0 PID: 11771 Comm: syz.6.1383 Tainted: G S                  syzkaller #0 PREEMPT(full) 
Tainted: [S]=CPU_OUT_OF_SPEC
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
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 ignore_event+0x83e/0xaa0 kernel/trace/trace.c:2526
 trace_event_printf+0xb5/0x160 kernel/trace/trace_output.c:356
 trace_raw_output_sys_enter+0x4c/0x60 include/trace/events/syscalls.h:18
 print_trace_fmt kernel/trace/trace.c:3071 [inline]
 print_trace_line+0x97d/0x1790 kernel/trace/trace.c:3237
 tracing_read_pipe+0x586/0xd60 kernel/trace/trace.c:5444
 vfs_read+0x1e4/0xb40 fs/read_write.c:572
 ksys_read+0x12a/0x250 fs/read_write.c:716
 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: 0033:0x7f48cdd9e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f48cebb5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f48ce025fa0 RCX: 00007f48cdd9e019
RDX: 0000000000002000 RSI: 0000200000001000 RDI: 0000000000000003
RBP: 00007f48cde3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f48ce026038 R14: 00007f48ce025fa0 R15: 00007ffe7508fde8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4705a
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00009a6048 ffffea00007bac08 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x44dc0(GFP_KERNEL|__GFP_ZERO|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 9023, tgid 9022 (syz.6.770), ts 304966657874, free_ts 587151444439
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859
 prep_new_page mm/page_alloc.c:1867 [inline]
 get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304
 __alloc_pages_noprof+0xb/0x110 mm/page_alloc.c:5338
 __alloc_pages_node_noprof include/linux/gfp.h:291 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:318 [inline]
 alloc_cpu_data+0x60/0x160 kernel/trace/ring_buffer.c:427
 __rb_allocate_pages+0xbd5/0x10a0 kernel/trace/ring_buffer.c:2436
 ring_buffer_resize+0x6df/0x1e80 kernel/trace/ring_buffer.c:3270
 __tracing_resize_ring_buffer.part.0+0x52/0x1f0 kernel/trace/trace.c:4738
 __tracing_resize_ring_buffer kernel/trace/trace.c:4732 [inline]
 tracing_update_buffers+0xd4/0xf0 kernel/trace/trace.c:4977
 event_enable_write+0x23f/0x340 kernel/trace/trace_events.c:1926
 vfs_write+0x2aa/0x1050 fs/read_write.c:685
 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
page last free pid 11775 tgid 11774 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1406 [inline]
 __free_frozen_pages+0x79f/0x1090 mm/page_alloc.c:2950
 free_buffer_page kernel/trace/ring_buffer.c:398 [inline]
 ring_buffer_subbuf_order_set+0x12d5/0x18a0 kernel/trace/ring_buffer.c:7439
 buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221
 vfs_write+0x2aa/0x1050 fs/read_write.c:685
 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

Memory state around the buggy address:
 ffff88804705a080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804705a100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804705a180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                  ^
 ffff88804705a200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804705a280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/31 07:19 upstream 3708dd948844 aaffb173 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in ignore_event
* Struck through repros no longer work on HEAD.