[syzbot] [serial?] KASAN: slab-out-of-bounds Write in do_con_write (2)

[syzbot <syzbot+1046ca04f5ba70aa8206@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    c8ed9b5c02a5 Merge tag 'drm-fixes-2025-09-05' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=110ca962580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fecbb496f75d3d61
dashboard link: https://syzkaller.appspot.com/bug?extid=1046ca04f5ba70aa8206
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4da8d56aff3a/disk-c8ed9b5c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1366baa37dbc/vmlinux-c8ed9b5c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0674b31d870d/bzImage-c8ed9b5c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1046ca04f5ba70aa8206@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in vc_con_write_normal drivers/tty/vt/vt.c:3086 [inline]
BUG: KASAN: slab-out-of-bounds in do_con_write+0x3839/0x8280 drivers/tty/vt/vt.c:3178
Write of size 2 at addr ffff88803467ff96 by task syz.3.1321/12594

CPU: 0 UID: 0 PID: 12594 Comm: syz.3.1321 Tainted: G     U              syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 vc_con_write_normal drivers/tty/vt/vt.c:3086 [inline]
 do_con_write+0x3839/0x8280 drivers/tty/vt/vt.c:3178
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3516
 process_output_block drivers/tty/n_tty.c:561 [inline]
 n_tty_write+0x41c/0x11e0 drivers/tty/n_tty.c:2377
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write.constprop.0+0x504/0x9b0 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+0xd4/0x150 drivers/tty/tty_io.c:1105
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d3/0x11d0 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efc5798ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007efc58815038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007efc57bc5fa0 RCX: 00007efc5798ebe9
RDX: 0000000000000028 RSI: 00002000000005c0 RDI: 0000000000000003
RBP: 00007efc57a11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efc57bc6038 R14: 00007efc57bc5fa0 R15: 00007ffe3160a858
 </TASK>

Allocated by task 5865:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:405
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4376 [inline]
 __kvmalloc_node_noprof+0x27b/0x620 mm/slub.c:5067
 netif_alloc_rx_queues net/core/dev.c:10936 [inline]
 alloc_netdev_mqs+0xc82/0x1530 net/core/dev.c:11882
 rtnl_create_link+0xc08/0xf90 net/core/rtnetlink.c:3633
 rtnl_newlink_create net/core/rtnetlink.c:3815 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0xb69/0x2000 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 __sys_sendto+0x4a0/0x520 net/socket.c:2228
 __do_sys_sendto net/socket.c:2235 [inline]
 __se_sys_sendto net/socket.c:2231 [inline]
 __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2231
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88803467e000
 which belongs to the cache kmalloc-cg-4k of size 4096
The buggy address is located 3990 bytes to the right of
 allocated 4096-byte region [ffff88803467e000, ffff88803467f000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x34678
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b84b500 0000000000000000 0000000000000001
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b84b500 0000000000000000 0000000000000001
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000d19e01 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 5239, tgid 5239 (udevd), ts 58016202013, free_ts 57921496167
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:2492 [inline]
 allocate_slab mm/slub.c:2660 [inline]
 new_slab+0x247/0x330 mm/slub.c:2714
 ___slab_alloc+0xcf2/0x1750 mm/slub.c:3901
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3992
 __slab_alloc_node mm/slub.c:4067 [inline]
 slab_alloc_node mm/slub.c:4228 [inline]
 __do_kmalloc_node mm/slub.c:4375 [inline]
 __kvmalloc_node_noprof+0x3b1/0x620 mm/slub.c:5067
 seq_buf_alloc fs/seq_file.c:38 [inline]
 seq_read_iter+0x826/0x12c0 fs/seq_file.c:210
 kernfs_fop_read_iter+0x40f/0x5a0 fs/kernfs/file.c:279
 new_sync_read fs/read_write.c:491 [inline]
 vfs_read+0x8bf/0xcf0 fs/read_write.c:572
 ksys_read+0x12a/0x250 fs/read_write.c:715
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5242 tgid 5242 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
 discard_slab mm/slub.c:2758 [inline]
 __put_partials+0x165/0x1c0 mm/slub.c:3223
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4d/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:340
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4191 [inline]
 slab_alloc_node mm/slub.c:4240 [inline]
 __do_kmalloc_node mm/slub.c:4375 [inline]
 __kmalloc_noprof+0x1d4/0x510 mm/slub.c:4388
 kmalloc_noprof include/linux/slab.h:909 [inline]
 tomoyo_realpath_from_path+0xc2/0x6e0 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x274/0x460 security/tomoyo/file.c:822
 security_inode_getattr+0x116/0x290 security/security.c:2377
 vfs_getattr fs/stat.c:259 [inline]
 vfs_statx_path fs/stat.c:299 [inline]
 vfs_statx+0x121/0x3f0 fs/stat.c:356
 vfs_fstatat+0x7b/0xf0 fs/stat.c:375
 __do_sys_newfstatat+0x97/0x120 fs/stat.c:542
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88803467fe80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88803467ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88803467ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                         ^
 ffff888034680000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888034680080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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