[moderation] [fbdev?] KASAN: slab-out-of-bounds Read in vgacon_save_screen (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b29fb8829bff Merge tag 'v7.0-rc3-ksmbd-server-fixes' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17fa575a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=163cf0fb07ea84d3
dashboard link: https://syzkaller.appspot.com/bug?extid=d729083fe578e62c8603
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
CC: [del...@gmx.de dri-...@lists.freedesktop.org gre...@linuxfoundation.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/d031abe6d097/disk-b29fb882.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0357a6ee7a21/vmlinux-b29fb882.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e53eec9d067a/bzImage-b29fb882.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d72908...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in scr_memcpyw include/linux/vt_buffer.h:38 [inline]
BUG: KASAN: slab-out-of-bounds in vgacon_save_screen drivers/video/console/vgacon.c:1132 [inline]
BUG: KASAN: slab-out-of-bounds in vgacon_save_screen+0x1b8/0x230 drivers/video/console/vgacon.c:1114
Read of size 4000 at addr ffff88802369df60 by task syz.0.3269/20470

CPU: 0 UID: 0 PID: 20470 Comm: syz.0.3269 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026
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
check_region_inline mm/kasan/generic.c:186 [inline]
kasan_check_range+0x10f/0x1e0 mm/kasan/generic.c:200
__asan_memcpy+0x23/0x60 mm/kasan/shadow.c:105
scr_memcpyw include/linux/vt_buffer.h:38 [inline]
vgacon_save_screen drivers/video/console/vgacon.c:1132 [inline]
vgacon_save_screen+0x1b8/0x230 drivers/video/console/vgacon.c:1114
save_screen+0xc5/0x160 drivers/tty/vt/vt.c:886
do_bind_con_driver.isra.0+0x7e6/0x9c0 drivers/tty/vt/vt.c:3948
do_take_over_console+0x501/0x5d0 drivers/tty/vt/vt.c:4494
do_fbcon_takeover+0xe9/0x210 drivers/video/fbdev/core/fbcon.c:581
set_con2fb_map+0x862/0x1040 drivers/video/fbdev/core/fbcon.c:889
fbcon_set_con2fb_map_ioctl+0x16c/0x220 drivers/video/fbdev/core/fbcon.c:3146
do_fb_ioctl+0x25b/0x7e0 drivers/video/fbdev/core/fb_chrdev.c:138
fb_ioctl+0xe5/0x150 drivers/video/fbdev/core/fb_chrdev.c:169
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/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
RIP: 0033:0x7f777299c799
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:00007f7773885028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7772c16090 RCX: 00007f777299c799
RDX: 0000000000000000 RSI: 0000000000004610 RDI: 0000000000000007
RBP: 00007f7772a32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7772c16128 R14: 00007f7772c16090 R15: 00007ffd5c2cd558
</TASK>

Allocated by task 17013:
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:5263 [inline]
__kmalloc_node_track_caller_noprof+0x304/0x850 mm/slub.c:5371
kmalloc_reserve+0xe8/0x350 net/core/skbuff.c:635
__alloc_skb+0x185/0x710 net/core/skbuff.c:713
alloc_skb include/linux/skbuff.h:1383 [inline]
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:819 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:876 [inline]
nsim_dev_trap_report_work+0x2af/0xd10 drivers/net/netdevsim/dev.c:922
process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
process_scheduled_works kernel/workqueue.c:3358 [inline]
worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 17013:
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:2692 [inline]
slab_free mm/slub.c:6168 [inline]
kfree+0x1f6/0x6b0 mm/slub.c:6486
skb_kfree_head net/core/skbuff.c:1089 [inline]
skb_free_head+0x119/0x220 net/core/skbuff.c:1101
skb_release_data+0x79b/0x9d0 net/core/skbuff.c:1128
skb_release_all net/core/skbuff.c:1203 [inline]
__kfree_skb net/core/skbuff.c:1217 [inline]
consume_skb net/core/skbuff.c:1450 [inline]
consume_skb+0xc4/0x110 net/core/skbuff.c:1444
nsim_dev_trap_report drivers/net/netdevsim/dev.c:892 [inline]
nsim_dev_trap_report_work+0x8cf/0xd10 drivers/net/netdevsim/dev.c:922
process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
process_scheduled_works kernel/workqueue.c:3358 [inline]
worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88802369c000
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 [ffff88802369c000, ffff88802369d000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x23698
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 ffffea00008da601 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 5206, tgid 5206 (udevd), ts 52160108561, free_ts 52093031211
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:3296 [inline]
allocate_slab mm/slub.c:3485 [inline]
new_slab+0xa6/0x6c0 mm/slub.c:3543
refill_objects+0x26b/0x400 mm/slub.c:7178
refill_sheaf mm/slub.c:2818 [inline]
alloc_full_sheaf mm/slub.c:2839 [inline]
__pcs_replace_empty_main+0x1ab/0x600 mm/slub.c:4629
alloc_from_pcs mm/slub.c:4720 [inline]
slab_alloc_node mm/slub.c:4854 [inline]
__kmalloc_cache_noprof+0x493/0x6f0 mm/slub.c:5378
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
kernfs_iop_get_link fs/kernfs/symlink.c:137 [inline]
kernfs_iop_get_link+0x65/0x16a0 fs/kernfs/symlink.c:128
vfs_readlink+0x213/0x440 fs/namei.c:6237
do_readlinkat+0x250/0x370 fs/stat.c:583
__do_sys_readlink fs/stat.c:605 [inline]
__se_sys_readlink fs/stat.c:602 [inline]
__x64_sys_readlink+0x78/0xc0 fs/stat.c:602
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 5193 tgid 5193 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:4542 [inline]
slab_alloc_node mm/slub.c:4869 [inline]
kmem_cache_alloc_node_noprof+0x25a/0x6f0 mm/slub.c:4921
__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:
ffff88802369de00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802369de80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802369df00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88802369df80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802369e000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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