KASAN: slab-out-of-bounds Read in soft_cursor

Status: upstream: reported on 2026/10/05 14:46
Reported-by: syzbot+cb9e6745cee149931289@syzkaller.appspotmail.com
First crash: 8d01h, last: 8d01h
▶ ▼ Similar bugs (14)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: slab-out-of-bounds Read in soft_cursor 17 3 48d 81d 0/3 upstream: reported on 2026/07/24 00:48
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor (2) 17 syz, C done 8 1970d 2092d 1/1 fixed on 2021/06/23 17:43
linux-4.14 KASAN: slab-out-of-bounds Read in soft_cursor 17 syz, C unreliable 57 1974d 2506d 0/1 upstream: reported C repro on 2019/12/03 14:54
linux-5.15 KASAN: slab-out-of-bounds Read in soft_cursor 17 1 20d 20d 0/3 upstream: reported on 2026/09/23 15:50
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor 17 syz, C done 61 2168d 2506d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 252d 386d 0/29 auto-obsoleted due to no activity on 2026/05/14 02:42
upstream KASAN: slab-out-of-bounds Read in soft_cursor fbdev 17 syz, C done 218 2196d 2505d 15/29 fixed on 2020/11/16 12:12
upstream KASAN: global-out-of-bounds Read in soft_cursor (3) fbdev 19 190 5h49m 67d 28/29 upstream: reported on 2026/08/07 00:01
linux-5.15 KASAN: null-ptr-deref Read in soft_cursor origin:lts-only 11 syz error 1 1234d 1234d 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 syz, C inconclusive 7 1994d 2505d 0/1 upstream: reported C repro on 2019/12/04 13:11
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1235d 1235d 22/29 fixed on 2023/07/01 16:05
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 598d 594d 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 syz, C done 22 1967d 2434d 1/1 fixed on 2021/06/24 08:01
linux-4.14 KASAN: global-out-of-bounds Read in soft_cursor 17 syz, C error 19 1494d 2493d 0/1 upstream: reported C repro on 2019/12/16 00:09

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x37f/0xc30 drivers/video/fbdev/core/softcursor.c:70
Read of size 52 at addr ffff888079a93554 by task syz.5.1958/12470

CPU: 0 PID: 12470 Comm: syz.5.1958 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 soft_cursor+0x37f/0xc30 drivers/video/fbdev/core/softcursor.c:70
 ccw_cursor+0x1611/0x1ec0 drivers/video/fbdev/core/fbcon_ccw.c:380
 hide_cursor+0x7f/0x320 drivers/tty/vt/vt.c:855
 redraw_screen+0x200/0x1000 drivers/tty/vt/vt.c:960
 vc_do_resize+0x1256/0x17f0 drivers/tty/vt/vt.c:1291
 fbcon_do_set_font+0xb5c/0x1ae0 drivers/video/fbdev/core/fbcon.c:2440
 con_font_set drivers/tty/vt/vt.c:4629 [inline]
 con_font_op+0xc3c/0xf60 drivers/tty/vt/vt.c:4676
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:476 [inline]
 vt_ioctl+0x1a21/0x1f20 drivers/tty/vt/vt_ioctl.c:754
 tty_ioctl+0x91e/0xdc0 drivers/tty/tty_io.c:2779
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f69fd19e199
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:00007f69fdf96028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f69fd426090 RCX: 00007f69fd19e199
RDX: 0000200000000000 RSI: 0000000000004b72 RDI: 0000000000000005
RBP: 00007f69fd2350b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f69fd426128 R14: 00007f69fd426090 R15: 00007ffcfe0ba0b8
 </TASK>

Allocated by task 8902:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1007 [inline]
 __kmalloc+0xb7/0x240 mm/slab_common.c:1020
 kmalloc_array include/linux/slab.h:637 [inline]
 fbcon_rotate_font+0x3d6/0xdd0 drivers/video/fbdev/core/fbcon_rotate.c:53
 fbcon_switch+0xdf9/0x1f80 drivers/video/fbdev/core/fbcon.c:2146
 redraw_screen+0x585/0x1000 drivers/tty/vt/vt.c:969
 vc_do_resize+0x1256/0x17f0 drivers/tty/vt/vt.c:1291
 fbcon_modechanged+0x80d/0x12b0 drivers/video/fbdev/core/fbcon.c:2715
 fbcon_rotate_all drivers/video/fbdev/core/fbcon.c:252 [inline]
 store_rotate_all+0x531/0x620 drivers/video/fbdev/core/fbcon.c:3260
 kernfs_fop_write_iter+0x3a4/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888079a92000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1364 bytes to the right of
 allocated 4096-byte region [ffff888079a92000, ffff888079a93000)

The buggy address belongs to the physical page:
page:ffffea0001e6a400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x79a90
head:ffffea0001e6a400 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c42140 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000040004 00000001ffffffff 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 0x1d2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 1097, tgid 1097 (kworker/u4:7), ts 130761894058, free_ts 130712263521
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
 prep_new_page mm/page_alloc.c:1589 [inline]
 get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
 __alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
 alloc_slab_page+0x5d/0x180 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:2081
 ___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa4/0x230 mm/slab_common.c:1027
 kmalloc_reserve+0x116/0x240 net/core/skbuff.c:584
 __alloc_skb+0x138/0x2c0 net/core/skbuff.c:653
 alloc_skb include/linux/skbuff.h:1316 [inline]
 nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
 nsim_dev_trap_report_work+0x253/0xa90 drivers/net/netdevsim/dev.c:851
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1182 [inline]
 free_unref_page_prepare+0x7d7/0x8f0 mm/page_alloc.c:2366
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x319/0x400 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x17e/0x2c0 mm/slub.c:3519
 getname_flags+0xbb/0x500 fs/namei.c:140
 do_sys_openat2+0xda/0x1d0 fs/open.c:1416
 do_sys_open fs/open.c:1437 [inline]
 __do_sys_openat fs/open.c:1453 [inline]
 __se_sys_openat fs/open.c:1448 [inline]
 __x64_sys_openat+0x139/0x160 fs/open.c:1448
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff888079a93400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888079a93480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888079a93500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                 ^
 ffff888079a93580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888079a93600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/05 14:46 linux-6.6.y a91a6aa9253c af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/10/05 14:45 linux-6.6.y a91a6aa9253c af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in soft_cursor
* Struck through repros no longer work on HEAD.