KASAN: slab-use-after-free Read in ring_buffer_iter_advance

Status: upstream: reported on 2026/08/04 00:52
Subsystems: trace
Labels: prio:normal actionable
[Documentation on labels]
Reported-by: syzbot+e0cc44465d6bae735679@syzkaller.appspotmail.com
Fix commit: bf98d7b0d5a9 ring-buffer: Prevent subbuf order change when resizing is disabled
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-snapshot-upstream-root ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb], missing on: [ci-qemu-native-arm64-kvm ci-qemu2-riscv64 ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-rust-kasan-gce]
First crash: 16d, last: 16d
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
3f539c45 repro-c Reproduced: ✅ ❓ KASAN: slab-use-after-free Read in ring_buffer_iter_advance 2026/08/06 12:59 2026/08/07 08:39 2026/08/07 09:04 c38879ea
2fb69049 moderation Actionable: ✅ ❓ KASAN: slab-use-after-free Read in ring_buffer_iter_advance 2026/08/04 00:40 2026/08/04 00:40 2026/08/04 00:51 cb1adeae
19cd1299 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in ring_buffer_iter_advance 2026/08/01 00:55 2026/08/01 00:55 2026/08/01 01:01 7664cf44
▶ ▼ Discussions (4)
Title Replies (including bot) Last reply
[for-linus][PATCH 10/12] ring-buffer: Prevent subbuf order change when resizing is disabled 1 (1) 2026/08/09 02:31
[PATCH 2/6] ring-buffer: Prevent subbuf order change when resizing is disabled 1 (1) 2026/08/06 21:13
[syzbot] [trace?] KASAN: slab-use-after-free Read in ring_buffer_iter_advance 1 (2) 2026/08/06 12:58
[PATCH] ring-buffer: Prevent subbuf order change when resizing is disabled 3 (3) 2026/08/05 19:15

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in rb_page_size kernel/trace/ring_buffer.c:391 [inline]
BUG: KASAN: slab-use-after-free in rb_advance_iter+0x40e/0x460 kernel/trace/ring_buffer.c:6024
Read of size 8 at addr ffff88802d79b8b8 by task syz.4.389/6869

CPU: 0 UID: 0 PID: 6869 Comm: syz.4.389 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
 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
 rb_page_size kernel/trace/ring_buffer.c:391 [inline]
 rb_advance_iter+0x40e/0x460 kernel/trace/ring_buffer.c:6024
 ring_buffer_iter_advance+0x69/0x90 kernel/trace/ring_buffer.c:6445
 trace_find_next_entry_inc kernel/trace/trace.c:2679 [inline]
 s_next+0x270/0x410 kernel/trace/trace.c:2711
 seq_read_iter+0xac5/0x1270 fs/seq_file.c:263
 seq_read+0x344/0x4d0 fs/seq_file.c:163
 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: 0033:0x7f734c99df99
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:00007f734d820028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f734cc25fa0 RCX: 00007f734c99df99
RDX: 0000000000001000 RSI: 0000200000000340 RDI: 0000000000000005
RBP: 00007f734ca34ec4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f734cc26038 R14: 00007f734cc25fa0 R15: 00007ffcf813c748
 </TASK>

Allocated by task 6869:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5334 [inline]
 __kmalloc_node_noprof+0x339/0x830 mm/slub.c:5346
 _kmalloc_node_noprof include/linux/slab.h:1197 [inline]
 __rb_allocate_pages+0x399/0x10a0 kernel/trace/ring_buffer.c:2402
 ring_buffer_subbuf_order_set+0x3ef/0x18a0 kernel/trace/ring_buffer.c:7379
 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

Freed by task 6871:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x22b/0x6c0 mm/slub.c:6692
 free_buffer_page kernel/trace/ring_buffer.c:399 [inline]
 ring_buffer_subbuf_order_set+0x116b/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

The buggy address belongs to the object at ffff88802d79b880
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 56 bytes inside of
 freed 64-byte region [ffff88802d79b880, ffff88802d79b8c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2d79b
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fe238c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 13416095140, free_ts 0
 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_slab_page mm/slub.c:3266 [inline]
 allocate_slab mm/slub.c:3380 [inline]
 new_slab+0xa2/0x640 mm/slub.c:3426
 refill_objects+0xe3/0x410 mm/slub.c:7310
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x376/0x680 mm/slub.c:4675
 alloc_from_pcs mm/slub.c:4773 [inline]
 slab_alloc_node mm/slub.c:4905 [inline]
 __do_kmalloc_node mm/slub.c:5333 [inline]
 __kmalloc_noprof+0x66d/0x820 mm/slub.c:5359
 _kmalloc_noprof include/linux/slab.h:992 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 handler_new_ref+0x1ab/0xc60 drivers/media/v4l2-core/v4l2-ctrls-core.c:1895
 v4l2_ctrl_add_handler drivers/media/v4l2-core/v4l2-ctrls-core.c:2456 [inline]
 v4l2_ctrl_add_handler+0x223/0x300 drivers/media/v4l2-core/v4l2-ctrls-core.c:2430
 vivid_create_controls+0x33ce/0x3e80 drivers/media/test-drivers/vivid/vivid-ctrls.c:2072
 vivid_create_instance drivers/media/test-drivers/vivid/vivid-core.c:1933 [inline]
 vivid_probe.cold+0x4f1e/0x921e drivers/media/test-drivers/vivid/vivid-core.c:2095
 platform_probe+0x106/0x1d0 drivers/base/platform.c:1439
 call_driver_probe drivers/base/dd.c:628 [inline]
 really_probe+0x241/0xa60 drivers/base/dd.c:706
 __driver_probe_device+0x20e/0x450 drivers/base/dd.c:868
 driver_probe_device+0x4a/0x140 drivers/base/dd.c:898
 __driver_attach+0x21f/0x5b0 drivers/base/dd.c:1292
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88802d79b780: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88802d79b800: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff88802d79b880: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88802d79b900: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88802d79b980: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/30 12:54 upstream 11028ab62899 2377cd3d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: slab-use-after-free Read in ring_buffer_iter_advance
* Struck through repros no longer work on HEAD.