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

Status: upstream: reported on 2026/02/26 08:31
Subsystems: serial
[Documentation on labels]
Reported-by: syzbot+8e9c1abac3ceb45abffe@syzkaller.appspotmail.com
First crash: 67d, last: 2d06h
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[syzbot] Monthly serial report (Mar 2026) 0 (1) 2026/03/03 08:07
[syzbot] [serial?] KASAN: slab-out-of-bounds Write in do_con_write (3) 0 (1) 2026/02/26 08:31
▶ ▼ 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 187d 191d 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 324d 402d 0/29 auto-obsoleted due to no activity on 2025/08/04 16:13

Sample crash report:
netlink: 4 bytes leftover after parsing attributes in process `syz.3.2240'.
==================================================================
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+0x386f/0x8540 drivers/tty/vt/vt.c:3226
Write of size 2 at addr ffff88802695bf60 by task syz.3.2240/16271

CPU: 1 UID: 0 PID: 16271 Comm: syz.3.2240 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+0x386f/0x8540 drivers/tty/vt/vt.c:3226
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3558
 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: 0033:0x7f33bb79c799
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:00007f33b99f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f33bba16090 RCX: 00007f33bb79c799
RDX: 000000000000fdef RSI: 0000200000000000 RDI: 0000000000000009
RBP: 00007f33bb832c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f33bba16128 R14: 00007f33bba16090 R15: 00007fff4a9f45a8
 </TASK>

Allocated by task 6837:
 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:5260 [inline]
 __kmalloc_noprof+0x301/0x850 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 vc_do_resize+0x1da/0x10f0 drivers/tty/vt/vt.c:1177
 vc_resize include/linux/vt_kern.h:49 [inline]
 vgacon_init+0x386/0x440 drivers/video/console/vgacon.c:392
 visual_init+0x320/0x620 drivers/tty/vt/vt.c:1014
 do_bind_con_driver.isra.0+0x636/0x9c0 drivers/tty/vt/vt.c:3954
 do_unbind_con_driver+0x536/0x6a0 drivers/tty/vt/vt.c:4063
 vt_unbind drivers/tty/vt/vt.c:4149 [inline]
 store_bind+0x3f8/0x730 drivers/tty/vt/vt.c:4184
 dev_attr_store+0x58/0x80 drivers/base/core.c:2437
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
 do_iter_readv_writev+0x6ee/0x920 fs/read_write.c:829
 vfs_writev+0x360/0xe10 fs/read_write.c:1059
 do_writev+0x13e/0x340 fs/read_write.c:1105
 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 ffff88802695a000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 4032 bytes to the right of
 allocated 4000-byte region [ffff88802695a000, ffff88802695afa0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x26958
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 ffff88813fe3d140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe3d140 dead000000000100 dead000000000122
head: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea00009a5601 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 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6837, tgid 6836 (syz.2.208), ts 128294996840, free_ts 128238341897
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x153/0x170 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x111d/0x3140 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x27c/0x2ba0 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab mm/slub.c:3481 [inline]
 new_slab+0xa6/0x6b0 mm/slub.c:3539
 refill_objects+0x26b/0x400 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x1ab/0x660 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x688/0x850 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 tomoyo_realpath_from_path+0xb6/0x690 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_number_perm+0x23c/0x580 security/tomoyo/file.c:728
 security_file_ioctl+0xd3/0x230 security/security.c:2435
 __do_sys_ioctl fs/ioctl.c:591 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0xb7/0x210 fs/ioctl.c:583
 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
page last free pid 5817 tgid 5817 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0x7e1/0x10d0 mm/page_alloc.c:2978
 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:4538 [inline]
 slab_alloc_node mm/slub.c:4866 [inline]
 kmem_cache_alloc_node_noprof+0x25a/0x6f0 mm/slub.c:4918
 __alloc_skb+0x140/0x710 net/core/skbuff.c:702
 alloc_skb include/linux/skbuff.h:1383 [inline]
 netlink_alloc_large_skb+0x69/0x150 net/netlink/af_netlink.c:1184
 netlink_sendmsg+0x680/0xda0 net/netlink/af_netlink.c:1869
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 ____sys_sendmsg+0x9e1/0xb70 net/socket.c:2592
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2646
 __sys_sendmsg+0x170/0x220 net/socket.c:2678
 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:
 ffff88802695be00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802695be80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802695bf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                       ^
 ffff88802695bf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802695c000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/14 12:07 upstream 1c9982b49613 ee8d34d6 .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
2026/03/14 07:58 upstream 1c9982b49613 ee8d34d6 .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
2026/02/26 08:30 upstream d9d32e5bd5a4 e0f78d93 .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
2026/02/14 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.