[syzbot] [serial?] KASAN: slab-out-of-bounds Read in vc_uniscr_check

From: syzbot
Date: Fri Mar 07 2025 - 19:04:23 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 7eb172143d55 Linux 6.14-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14c4a7a0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bed8205d3b84ef81
dashboard link: https://syzkaller.appspot.com/bug?extid=ad83bc4086a46e2b322b
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/06a492964134/disk-7eb17214.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/83adeaa22219/vmlinux-7eb17214.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7386164633ed/bzImage-7eb17214.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ad83bc4086a46e2b322b@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: slab-out-of-bounds in vc_uniscr_check+0x4bf/0x5b0 drivers/tty/vt/vt.c:513
Read of size 2 at addr ffff888062b96760 by task syz.3.7501/793

CPU: 1 UID: 0 PID: 793 Comm: syz.3.7501 Not tainted 6.14.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
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:408 [inline]
print_report+0xc3/0x670 mm/kasan/report.c:521
kasan_report+0xd9/0x110 mm/kasan/report.c:634
vc_uniscr_check+0x4bf/0x5b0 drivers/tty/vt/vt.c:513
vcs_read_buf_uni drivers/tty/vt/vc_screen.c:254 [inline]
vcs_read+0x6c5/0xbd0 drivers/tty/vt/vc_screen.c:436
vfs_read+0x1df/0xbf0 fs/read_write.c:563
ksys_read+0x12b/0x250 fs/read_write.c:708
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa8c5d8d169
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:00007fa8c6c94038 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fa8c5fa5fa0 RCX: 00007fa8c5d8d169
RDX: 0000000000000080 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fa8c5e0e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fa8c5fa5fa0 R15: 00007fff5809c238
</TASK>

Allocated by task 31685:
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:377 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
kmalloc_noprof include/linux/slab.h:901 [inline]
kzalloc_noprof include/linux/slab.h:1037 [inline]
batadv_hardif_add_interface net/batman-adv/hard-interface.c:882 [inline]
batadv_hard_if_event+0xb94/0x1640 net/batman-adv/hard-interface.c:970
notifier_call_chain+0xb7/0x410 kernel/notifier.c:85
call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2206
call_netdevice_notifiers_extack net/core/dev.c:2244 [inline]
call_netdevice_notifiers net/core/dev.c:2258 [inline]
register_netdevice+0x17c2/0x1eb0 net/core/dev.c:10978
macvlan_common_newlink+0x1046/0x1940 drivers/net/macvlan.c:1536
rtnl_newlink_create net/core/rtnetlink.c:3796 [inline]
__rtnl_newlink net/core/rtnetlink.c:3907 [inline]
rtnl_newlink+0xb95/0x1d60 net/core/rtnetlink.c:4022
rtnetlink_rcv_msg+0x95b/0xea0 net/core/rtnetlink.c:6912
netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2533
netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1338
netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1882
sock_sendmsg_nosec net/socket.c:718 [inline]
__sock_sendmsg net/socket.c:733 [inline]
__sys_sendto+0x488/0x4f0 net/socket.c:2187
__do_sys_sendto net/socket.c:2194 [inline]
__se_sys_sendto net/socket.c:2190 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2190
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888062b96000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 1048 bytes to the right of
allocated 840-byte region [ffff888062b96000, ffff888062b96348)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888062b92000 pfn:0x62b90
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88801b041dc0 ffffea0001a1cc10 ffffea0000a5c210
raw: ffff888062b92000 0000000000100008 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88801b041dc0 ffffea0001a1cc10 ffffea0000a5c210
head: ffff888062b92000 0000000000100008 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea00018ae401 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
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 5831, tgid 5831 (syz-executor), ts 72139438838, free_ts 24347774881
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
prep_new_page mm/page_alloc.c:1559 [inline]
get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3477
__alloc_frozen_pages_noprof+0x221/0x2470 mm/page_alloc.c:4739
alloc_pages_mpol+0x1fc/0x540 mm/mempolicy.c:2270
alloc_slab_page mm/slub.c:2423 [inline]
allocate_slab mm/slub.c:2587 [inline]
new_slab+0x23d/0x330 mm/slub.c:2640
___slab_alloc+0xc5d/0x1720 mm/slub.c:3826
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3916
__slab_alloc_node mm/slub.c:3991 [inline]
slab_alloc_node mm/slub.c:4152 [inline]
__do_kmalloc_node mm/slub.c:4293 [inline]
__kmalloc_node_noprof+0x2f0/0x510 mm/slub.c:4300
kmalloc_node_noprof include/linux/slab.h:928 [inline]
qdisc_alloc+0xbb/0xc50 net/sched/sch_generic.c:947
qdisc_create_dflt+0x73/0x430 net/sched/sch_generic.c:1009
attach_one_default_qdisc net/sched/sch_generic.c:1175 [inline]
netdev_for_each_tx_queue include/linux/netdevice.h:2590 [inline]
attach_default_qdiscs net/sched/sch_generic.c:1193 [inline]
dev_activate+0x63a/0x12b0 net/sched/sch_generic.c:1252
__dev_open+0x3e4/0x540 net/core/dev.c:1644
__dev_change_flags+0x561/0x720 net/core/dev.c:9254
dev_change_flags+0x8f/0x160 net/core/dev.c:9326
do_setlink.constprop.0+0x699/0x3f80 net/core/rtnetlink.c:3118
rtnl_changelink net/core/rtnetlink.c:3733 [inline]
__rtnl_newlink net/core/rtnetlink.c:3885 [inline]
rtnl_newlink+0x1306/0x1d60 net/core/rtnetlink.c:4022
page last free pid 1 tgid 1 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1127 [inline]
free_frozen_pages+0x6db/0xfb0 mm/page_alloc.c:2660
free_contig_range+0x133/0x3f0 mm/page_alloc.c:6678
destroy_args+0x66f/0x830 mm/debug_vm_pgtable.c:1017
debug_vm_pgtable+0x130f/0x2d60 mm/debug_vm_pgtable.c:1397
do_one_initcall+0x128/0x700 init/main.c:1257
do_initcall_level init/main.c:1319 [inline]
do_initcalls init/main.c:1335 [inline]
do_basic_setup init/main.c:1354 [inline]
kernel_init_freeable+0x5c7/0x900 init/main.c:1568
kernel_init+0x1c/0x2b0 init/main.c:1457
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Memory state around the buggy address:
ffff888062b96600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888062b96680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888062b96700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff888062b96780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888062b96800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

---
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Next message: Boqun Feng: "Re: [PATCH locking 00/11] LOCKDEP and Rust locking changes for v6.15"
Previous message: syzbot: "[syzbot] [selinux?] KCSAN: data-race in selinux_socket_post_create / selinux_socket_sock_rcv_skb"
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