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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: be48bcf004f9 Merge tag 'for-6.17-rc2-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1055a7a2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fecbb496f75d3d61
dashboard link: https://syzkaller.appspot.com/bug?extid=f16f353b701fe8be7445
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2c3a6bd5dc97/disk-be48bcf0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ecf3bb068fc8/vmlinux-be48bcf0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/65a5f2dd3ffb/bzImage-be48bcf0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f16f35...@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 ffff888079119f60 by task syz.0.1742/14459

CPU: 0 UID: 0 PID: 14459 Comm: syz.0.1742 Not tainted syzkaller #0 PREEMPT(full)
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+0x41f/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: 0033:0x7f940db8ebe9
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:00007f940ea1a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f940ddb6090 RCX: 00007f940db8ebe9
RDX: 0000000000000004 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007f940dc11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f940ddb6128 R14: 00007f940ddb6090 R15: 00007ffc29431ec8
</TASK>

Allocated by task 12277:
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:4365 [inline]
__kmalloc_node_track_caller_noprof+0x221/0x510 mm/slub.c:4384
kmalloc_reserve+0xef/0x2c0 net/core/skbuff.c:600
__alloc_skb+0x166/0x380 net/core/skbuff.c:669
alloc_skb include/linux/skbuff.h:1336 [inline]
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:763 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:820 [inline]
nsim_dev_trap_report_work+0x2b1/0xcf0 drivers/net/netdevsim/dev.c:866
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c2/0x780 kernel/kthread.c:463
ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 12277:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x60/0x70 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2417 [inline]
slab_free mm/slub.c:4680 [inline]
kfree+0x2b4/0x4d0 mm/slub.c:4879
skb_kfree_head net/core/skbuff.c:1047 [inline]
skb_free_head+0x114/0x210 net/core/skbuff.c:1059
skb_release_data+0x795/0x9e0 net/core/skbuff.c:1086
skb_release_all net/core/skbuff.c:1151 [inline]
__kfree_skb net/core/skbuff.c:1165 [inline]
consume_skb net/core/skbuff.c:1397 [inline]
consume_skb+0xbf/0x100 net/core/skbuff.c:1391
nsim_dev_trap_report drivers/net/netdevsim/dev.c:836 [inline]
nsim_dev_trap_report_work+0x8bd/0xcf0 drivers/net/netdevsim/dev.c:866
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c2/0x780 kernel/kthread.c:463
ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888079118000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 3936 bytes to the right of
allocated 4096-byte region [ffff888079118000, ffff888079119000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x79118
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 ffff88801b842140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b842140 dead000000000100 dead000000000122
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001e44601 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 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 49, tgid 49 (kworker/u8:3), ts 108977261943, free_ts 107143244344
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:2487 [inline]
allocate_slab mm/slub.c:2655 [inline]
new_slab+0x247/0x330 mm/slub.c:2709
___slab_alloc+0xcf2/0x1740 mm/slub.c:3891
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3981
__slab_alloc_node mm/slub.c:4056 [inline]
slab_alloc_node mm/slub.c:4217 [inline]
__do_kmalloc_node mm/slub.c:4364 [inline]
__kmalloc_node_track_caller_noprof+0x2ee/0x510 mm/slub.c:4384
kmalloc_reserve+0xef/0x2c0 net/core/skbuff.c:600
__alloc_skb+0x166/0x380 net/core/skbuff.c:669
alloc_skb include/linux/skbuff.h:1336 [inline]
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:763 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:820 [inline]
nsim_dev_trap_report_work+0x2b1/0xcf0 drivers/net/netdevsim/dev.c:866
process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c2/0x780 kernel/kthread.c:463
ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page last free pid 5231 tgid 5231 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:2753 [inline]
__put_partials+0x165/0x1c0 mm/slub.c:3218
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:4180 [inline]
slab_alloc_node mm/slub.c:4229 [inline]
kmem_cache_alloc_noprof+0x1cb/0x3b0 mm/slub.c:4236
getname_flags.part.0+0x4c/0x550 fs/namei.c:146
getname_flags+0x93/0xf0 include/linux/audit.h:322
do_readlinkat+0xb4/0x3a0 fs/stat.c:575
__do_sys_readlink fs/stat.c:613 [inline]
__se_sys_readlink fs/stat.c:610 [inline]
__x64_sys_readlink+0x78/0xc0 fs/stat.c:610
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:
ffff888079119e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888079119e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888079119f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff888079119f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88807911a000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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