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KASAN: slab-out-of-bounds Read in soft_cursor (2)

Status: upstream: reported on 2025/09/22 12:50
Subsystems: fbdev
[Documentation on labels]
Reported-by: syzbot+ae44b38396335bd847cd@syzkaller.appspotmail.com
First crash: 101d, last: 19d
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[syzbot] Monthly fbdev report (Dec 2025) 0 (1) 2025/12/16 01:32
[syzbot] [fbdev?] KASAN: slab-out-of-bounds Read in soft_cursor (2) 0 (1) 2025/09/22 12:50
▶ ▼ Similar bugs (11)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor (2) 17 C done 8 1679d 1801d 1/1 fixed on 2021/06/23 17:43
linux-4.14 KASAN: slab-out-of-bounds Read in soft_cursor 17 C unreliable 57 1684d 2215d 0/1 upstream: reported C repro on 2019/12/03 14:54
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor 17 C done 61 1877d 2215d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor fbdev 17 C done 218 1905d 2214d 15/29 fixed on 2020/11/16 12:12
linux-5.15 KASAN: null-ptr-deref Read in soft_cursor origin:lts-only 11 syz error 1 943d 943d 0/3 auto-obsoleted due to no activity on 2024/12/24 15:39
linux-4.14 KASAN: use-after-free Read in soft_cursor 19 C inconclusive 7 1703d 2214d 0/1 upstream: reported C repro on 2019/12/04 13:11
upstream general protection fault in soft_cursor fbdev 11 C 3 944d 944d 22/29 fixed on 2023/07/01 16:05
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 307d 303d 0/29 auto-obsoleted due to no activity on 2025/05/23 01:13
linux-4.19 KASAN: global-out-of-bounds Read in soft_cursor 17 C done 22 1676d 2144d 1/1 fixed on 2021/06/24 08:01
linux-4.14 KASAN: global-out-of-bounds Read in soft_cursor 17 C error 19 1203d 2202d 0/1 upstream: reported C repro on 2019/12/16 00:09
upstream KASAN: global-out-of-bounds Read in soft_cursor fbdev 17 11 1980d 2206d 0/29 auto-closed as invalid on 2020/11/22 03:01

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x458/0xa10 drivers/video/fbdev/core/softcursor.c:70
Read of size 26 at addr ffff888026dbe2cc by task syz.3.1565/16817

CPU: 0 UID: 0 PID: 16817 Comm: syz.3.1565 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
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
 check_region_inline mm/kasan/generic.c:194 [inline]
 kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:200
 __asan_memcpy+0x23/0x60 mm/kasan/shadow.c:105
 soft_cursor+0x458/0xa10 drivers/video/fbdev/core/softcursor.c:70
 bit_cursor+0xe8c/0x17e0 drivers/video/fbdev/core/bitblit.c:395
 fbcon_cursor+0x40c/0x5a0 drivers/video/fbdev/core/fbcon.c:1357
 hide_cursor+0x87/0x220 drivers/tty/vt/vt.c:855
 do_con_write+0x240c/0x8290 drivers/tty/vt/vt.c:3204
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3565
 process_output_block drivers/tty/n_tty.c:561 [inline]
 n_tty_write+0x41e/0x11e0 drivers/tty/n_tty.c:2377
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write.constprop.0+0x503/0x9b0 drivers/tty/tty_io.c:1081
 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/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe69a18f7c9
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:00007fe69b094038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fe69a3e5fa0 RCX: 00007fe69a18f7c9
RDX: 0000000000001006 RSI: 0000200000001040 RDI: 0000000000000004
RBP: 00007fe69a213f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe69a3e6038 R14: 00007fe69a3e5fa0 R15: 00007fffeee020b8
 </TASK>

Allocated by task 13006:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
 kasan_save_track+0x14/0x30 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5650 [inline]
 __kmalloc_noprof+0x32f/0x880 mm/slub.c:5662
 kmalloc_noprof include/linux/slab.h:961 [inline]
 fbcon_set_font+0x42e/0xc90 drivers/video/fbdev/core/fbcon.c:2538
 con_font_set drivers/tty/vt/vt.c:4919 [inline]
 con_font_op+0x77e/0x1040 drivers/tty/vt/vt.c:4959
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:472 [inline]
 vt_ioctl+0x48f/0x30a0 drivers/tty/vt/vt_ioctl.c:743
 tty_ioctl+0x661/0x1680 drivers/tty/tty_io.c:2792
 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+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888026dbc000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 2236 bytes to the right of
 allocated 6672-byte region [ffff888026dbc000, ffff888026dbda10)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x26db8
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 ffff88801b443180 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b443180 dead000000000100 dead000000000122
head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea00009b6e01 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 5298, tgid 5298 (kworker/u33:1), ts 65073586911, free_ts 65066097360
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1af/0x220 mm/page_alloc.c:1845
 prep_new_page mm/page_alloc.c:1853 [inline]
 get_page_from_freelist+0x10a3/0x3a30 mm/page_alloc.c:3879
 __alloc_frozen_pages_noprof+0x25f/0x2470 mm/page_alloc.c:5178
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:3059 [inline]
 allocate_slab mm/slub.c:3232 [inline]
 new_slab+0x24a/0x360 mm/slub.c:3286
 ___slab_alloc+0xd79/0x1a50 mm/slub.c:4655
 __slab_alloc.constprop.0+0x63/0x110 mm/slub.c:4778
 __slab_alloc_node mm/slub.c:4854 [inline]
 slab_alloc_node mm/slub.c:5276 [inline]
 __kmalloc_cache_noprof+0x477/0x780 mm/slub.c:5766
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 __hci_conn_add+0x14f/0x1af0 net/bluetooth/hci_conn.c:959
 hci_conn_add_unset+0x6d/0x100 net/bluetooth/hci_conn.c:1072
 le_conn_complete_evt+0x657/0x2150 net/bluetooth/hci_event.c:5673
 hci_le_conn_complete_evt+0x23c/0x370 net/bluetooth/hci_event.c:5825
 hci_le_meta_evt+0x357/0x5e0 net/bluetooth/hci_event.c:7278
 hci_event_func net/bluetooth/hci_event.c:7586 [inline]
 hci_event_packet+0x685/0x11c0 net/bluetooth/hci_event.c:7643
 hci_rx_work+0x2c9/0xeb0 net/bluetooth/hci_core.c:4076
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
page last free pid 5955 tgid 5950 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 __free_frozen_pages+0x7df/0x1160 mm/page_alloc.c:2901
 discard_slab mm/slub.c:3330 [inline]
 __put_partials+0x130/0x170 mm/slub.c:3876
 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:352
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4978 [inline]
 slab_alloc_node mm/slub.c:5288 [inline]
 kmem_cache_alloc_node_noprof+0x28a/0x770 mm/slub.c:5340
 __alloc_skb+0x2b2/0x380 net/core/skbuff.c:660
 alloc_skb include/linux/skbuff.h:1383 [inline]
 bt_skb_alloc include/net/bluetooth/bluetooth.h:510 [inline]
 vhci_get_user drivers/bluetooth/hci_vhci.c:496 [inline]
 vhci_write+0xc1/0x480 drivers/bluetooth/hci_vhci.c:616
 do_iter_readv_writev+0x662/0x9e0 fs/read_write.c:827
 vfs_writev+0x35f/0xde0 fs/read_write.c:1057
 do_writev+0x132/0x340 fs/read_write.c:1103
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888026dbe180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888026dbe200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888026dbe280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                              ^
 ffff888026dbe300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888026dbe380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/29 02:55 upstream e538109ac71d d1b870e1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in soft_cursor
2025/09/15 23:41 upstream f83ec76bf285 e2beed91 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in soft_cursor
2025/09/26 13:23 linux-next 8e2755d7779a 0abd0691 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-out-of-bounds Read in soft_cursor
2025/11/20 01:24 upstream 8b690556d8fe 26ee5237 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: global-out-of-bounds Read in soft_cursor
2025/12/06 20:34 upstream 416f99c3b16f d1b870e1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 KASAN: global-out-of-bounds Read in soft_cursor
2025/12/06 20:08 upstream 416f99c3b16f d1b870e1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 KASAN: global-out-of-bounds Read in soft_cursor
2025/10/20 12:45 upstream 211ddde0823f 1c8c8cd8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 KASAN: global-out-of-bounds Read in soft_cursor
* Struck through repros no longer work on HEAD.