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KASAN: slab-out-of-bounds Write in do_con_write (3)

Status: moderation: reported on 2026/01/11 21:51
Subsystems: serial
[Documentation on labels]
Reported-by: syzbot+40b8f12e9f9080f59990@syzkaller.appspotmail.com
First crash: 42d, last: 4d20h
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Write in do_con_write (2) serial 21 6 161d 165d 0/29 auto-obsoleted due to no activity on 2025/12/19 08:09
upstream KASAN: slab-out-of-bounds Write in do_con_write serial 21 4 298d 376d 0/29 auto-obsoleted due to no activity on 2025/08/04 16:13

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in vc_con_write_normal drivers/tty/vt/vt.c:3135 [inline]
BUG: KASAN: slab-out-of-bounds in do_con_write+0x3874/0x8550 drivers/tty/vt/vt.c:3226
Write of size 2 at addr ffff888022723a70 by task syz.3.1404/12588

CPU: 0 UID: 0 PID: 12588 Comm: syz.3.1404 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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+0x156/0x4c9 mm/kasan/report.c:482
 kasan_report+0xdf/0x1e0 mm/kasan/report.c:595
 vc_con_write_normal drivers/tty/vt/vt.c:3135 [inline]
 do_con_write+0x3874/0x8550 drivers/tty/vt/vt.c:3226
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3559
 process_output_block drivers/tty/n_tty.c:557 [inline]
 n_tty_write+0x44f/0x12d0 drivers/tty/n_tty.c:2366
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write.isra.0+0x4d2/0x890 drivers/tty/tty_io.c:1081
 tty_write drivers/tty/tty_io.c:1102 [inline]
 redirected_tty_write drivers/tty/tty_io.c:1125 [inline]
 redirected_tty_write+0xd4/0x120 drivers/tty/tty_io.c:1105
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f68f099bf79
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:00007f68f1859028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f68f0c16180 RCX: 00007f68f099bf79
RDX: 000000000000fdef RSI: 0000200000000000 RDI: 0000000000000006
RBP: 00007f68f0a327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f68f0c16218 R14: 00007f68f0c16180 R15: 00007ffeec7775c8
 </TASK>

Allocated by task 5815:
 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:5177 [inline]
 __kmalloc_noprof+0x301/0x850 mm/slub.c:5189
 kmalloc_noprof include/linux/slab.h:966 [inline]
 tomoyo_realpath_from_path+0xb6/0x690 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path2_perm+0x366/0x700 security/tomoyo/file.c:928
 tomoyo_path_rename+0xfc/0x1a0 security/tomoyo/tomoyo.c:300
 security_path_rename+0x18e/0x3c0 security/security.c:1518
 filename_renameat2+0x731/0xa60 fs/namei.c:6139
 __do_sys_rename fs/namei.c:6188 [inline]
 __se_sys_rename fs/namei.c:6184 [inline]
 __x64_sys_rename+0x81/0xb0 fs/namei.c:6184
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5815:
 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:2670 [inline]
 slab_free mm/slub.c:6082 [inline]
 kfree+0x1f6/0x6b0 mm/slub.c:6399
 tomoyo_realpath_from_path+0x19c/0x690 security/tomoyo/realpath.c:286
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path2_perm+0x366/0x700 security/tomoyo/file.c:928
 tomoyo_path_rename+0xfc/0x1a0 security/tomoyo/tomoyo.c:300
 security_path_rename+0x18e/0x3c0 security/security.c:1518
 filename_renameat2+0x731/0xa60 fs/namei.c:6139
 __do_sys_rename fs/namei.c:6188 [inline]
 __se_sys_rename fs/namei.c:6184 [inline]
 __x64_sys_rename+0x81/0xb0 fs/namei.c:6184
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888022722000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2672 bytes to the right of
 allocated 4096-byte region [ffff888022722000, ffff888022723000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x22720
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fe37140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe37140 dead000000000100 dead000000000122
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea000089c801 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5193, tgid 5193 (udevadm), ts 27779442158, free_ts 27772553095
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x153/0x170 mm/page_alloc.c:1888
 prep_new_page mm/page_alloc.c:1896 [inline]
 get_page_from_freelist+0x111d/0x3140 mm/page_alloc.c:3961
 __alloc_frozen_pages_noprof+0x27c/0x2ba0 mm/page_alloc.c:5249
 alloc_slab_page mm/slub.c:3238 [inline]
 allocate_slab mm/slub.c:3411 [inline]
 new_slab+0xa6/0x6e0 mm/slub.c:3469
 refill_objects+0x26b/0x400 mm/slub.c:7091
 refill_sheaf mm/slub.c:2787 [inline]
 alloc_full_sheaf mm/slub.c:2808 [inline]
 __pcs_replace_empty_main+0x19f/0x600 mm/slub.c:4546
 alloc_from_pcs mm/slub.c:4639 [inline]
 slab_alloc_node mm/slub.c:4773 [inline]
 __kmalloc_cache_noprof+0x493/0x6f0 mm/slub.c:5292
 kmalloc_noprof include/linux/slab.h:962 [inline]
 kzalloc_noprof include/linux/slab.h:1204 [inline]
 kobject_uevent_env+0x263/0x18b0 lib/kobject_uevent.c:540
 kobject_synth_uevent+0x6f0/0x7d0 lib/kobject_uevent.c:207
 uevent_store+0x46/0x90 drivers/base/bus.c:675
 drv_attr_store+0x74/0xb0 drivers/base/bus.c:125
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
page last free pid 5193 tgid 5193 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1432 [inline]
 __free_frozen_pages+0x7ca/0x10a0 mm/page_alloc.c:2977
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xe0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4459 [inline]
 slab_alloc_node mm/slub.c:4788 [inline]
 kmem_cache_alloc_noprof+0x241/0x6e0 mm/slub.c:4795
 seq_open+0x55/0x170 fs/seq_file.c:64
 kernfs_fop_open+0x590/0xd50 fs/kernfs/file.c:704
 do_dentry_open+0x6d8/0x1660 fs/open.c:949
 vfs_open+0x82/0x3f0 fs/open.c:1081
 do_open fs/namei.c:4671 [inline]
 path_openat+0x208c/0x31a0 fs/namei.c:4830
 do_file_open+0x20e/0x430 fs/namei.c:4859
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888022723900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888022723980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888022723a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                             ^
 ffff888022723a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888022723b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/14 07:12 upstream 770aaedb461a 1e62d198 .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto KASAN: slab-out-of-bounds Write in do_con_write
2026/02/08 03:49 upstream e7aa57247700 4c131dc4 .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto KASAN: slab-out-of-bounds Write in do_con_write
2026/01/30 20:27 upstream 4d310797262f ea6dba22 .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto KASAN: slab-out-of-bounds Write in do_con_write
2026/01/07 21:49 upstream f0b9d8eb98df d1b870e1 .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto KASAN: slab-out-of-bounds Write in do_con_write
* Struck through repros no longer work on HEAD.