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

Status: upstream: reported on 2026/07/24 00:48
Reported-by: syzbot+1c89534b655bcf1739e4@syzkaller.appspotmail.com
First crash: 21d, last: 12h17m
▶ ▼ Similar bugs (12)
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 syz, C done 8 1910d 2032d 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 1914d 2446d 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 syz, C done 61 2107d 2446d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 192d 326d 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 2136d 2444d 15/29 fixed on 2020/11/16 12:12
upstream KASAN: global-out-of-bounds Read in soft_cursor (3) fbdev 19 17 1d09h 7d14h 22/29 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 1174d 1174d 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 1934d 2445d 0/1 upstream: reported C repro on 2019/12/04 13:11
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1175d 1175d 22/29 fixed on 2023/07/01 16:05
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 538d 534d 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 1907d 2374d 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 1434d 2433d 0/1 upstream: reported C repro on 2019/12/16 00:09

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x37b/0xc30 drivers/video/fbdev/core/softcursor.c:70
Read of size 18 at addr ffff888026e8b1dc by task syz.3.5470/25105

CPU: 1 PID: 25105 Comm: syz.3.5470 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x235/0x290 mm/kasan/generic.c:189
 memcpy+0x25/0x60 mm/kasan/shadow.c:65
 soft_cursor+0x37b/0xc30 drivers/video/fbdev/core/softcursor.c:70
 cw_cursor+0x1f4f/0x2b20 drivers/video/fbdev/core/fbcon_cw.c:363
 hide_cursor+0x7f/0x320 drivers/tty/vt/vt.c:907
 redraw_screen+0x1fc/0x1000 drivers/tty/vt/vt.c:1012
 vc_do_resize+0x122c/0x17b0 drivers/tty/vt/vt.c:1342
 fbcon_do_set_font+0xb5c/0x1ae0 drivers/video/fbdev/core/fbcon.c:2446
 con_font_set drivers/tty/vt/vt.c:4678 [inline]
 con_font_op+0xac1/0xdb0 drivers/tty/vt/vt.c:4724
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]
 vt_ioctl+0x1635/0x1cc0 drivers/tty/vt/vt_ioctl.c:752
 tty_ioctl+0x7e6/0xba0 drivers/tty/tty_io.c:2776
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc3ded9e0d9
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:00007fc3dfca8028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc3df025fa0 RCX: 00007fc3ded9e0d9
RDX: 0000200000000180 RSI: 0000000000004b72 RDI: 0000000000000003
RBP: 00007fc3dee35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc3df026038 R14: 00007fc3df025fa0 R15: 00007fffec6f67c8
 </TASK>

Allocated by task 10352:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:936 [inline]
 __kmalloc+0xb3/0x240 mm/slab_common.c:949
 kmalloc_array include/linux/slab.h:615 [inline]
 fbcon_rotate_font+0x3d2/0xdd0 drivers/video/fbdev/core/fbcon_rotate.c:53
 fbcon_switch+0xdf5/0x1f80 drivers/video/fbdev/core/fbcon.c:2154
 redraw_screen+0x581/0x1000 drivers/tty/vt/vt.c:1021
 vc_do_resize+0x122c/0x17b0 drivers/tty/vt/vt.c:1342
 fbcon_modechanged+0x80d/0x12b0 drivers/video/fbdev/core/fbcon.c:2728
 fbcon_rotate_all drivers/video/fbdev/core/fbcon.c:250 [inline]
 store_rotate_all+0x52d/0x620 drivers/video/fbdev/core/fbcon.c:3267
 kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x482/0x9a0 fs/read_write.c:584
 ksys_write+0x14d/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888026e8a000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 476 bytes to the right of
 4096-byte region [ffff888026e8a000, ffff888026e8b000)

The buggy address belongs to the physical page:
page:ffffea00009ba200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x26e88
head:ffffea00009ba200 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888017442140
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 0x1d2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 10352, tgid 10351 (syz.0.1456), ts 652053058230, free_ts 651939352130
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2560
 prep_new_page mm/page_alloc.c:2567 [inline]
 get_page_from_freelist+0x206b/0x2180 mm/page_alloc.c:4358
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5658
 alloc_slab_page+0x5d/0x180 mm/slub.c:1799
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:1997
 ___slab_alloc+0xbc5/0x1240 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x126/0x270 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc+0xa3/0x240 mm/slab_common.c:949
 kmalloc include/linux/slab.h:568 [inline]
 tomoyo_realpath_from_path+0xe2/0x5c0 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_check_open_permission+0x212/0x440 security/tomoyo/file.c:771
 security_file_open+0x5e/0xa0 security/security.c:1682
 do_dentry_open+0x2fd/0x10b0 fs/open.c:869
 do_open fs/namei.c:3634 [inline]
 path_openat+0x2674/0x2f10 fs/namei.c:3791
 do_filp_open+0x1ee/0x420 fs/namei.c:3818
 do_sys_openat2+0x14b/0x4f0 fs/open.c:1320
 do_sys_open fs/open.c:1336 [inline]
 __do_sys_openat fs/open.c:1352 [inline]
 __se_sys_openat fs/open.c:1347 [inline]
 __x64_sys_openat+0x135/0x160 fs/open.c:1347
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1487 [inline]
 free_pcp_prepare mm/page_alloc.c:1537 [inline]
 free_unref_page_prepare+0x8e5/0x9e0 mm/page_alloc.c:3414
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3509
 free_slab mm/slub.c:2036 [inline]
 discard_slab mm/slub.c:2042 [inline]
 __unfreeze_partials+0x188/0x1e0 mm/slub.c:2591
 put_cpu_partial+0x17c/0x250 mm/slub.c:2667
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook+0x4b/0x490 mm/slab.h:737
 slab_alloc_node mm/slub.c:3359 [inline]
 slab_alloc mm/slub.c:3367 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3374 [inline]
 kmem_cache_alloc+0x18b/0x2f0 mm/slub.c:3383
 kmem_cache_zalloc include/linux/slab.h:689 [inline]
 __kernfs_new_node+0xe1/0x7f0 fs/kernfs/dir.c:614
 kernfs_new_node+0x148/0x250 fs/kernfs/dir.c:690
 __kernfs_create_file+0x47/0x2e0 fs/kernfs/file.c:1068
 sysfs_add_bin_file_mode_ns fs/sysfs/file.c:333 [inline]
 sysfs_create_bin_file+0x2cd/0x3c0 fs/sysfs/file.c:574
 usb_create_sysfs_dev_files+0x28/0x400 drivers/usb/core/sysfs.c:1021
 usb_bus_notify+0xd7/0x110 drivers/usb/core/usb.c:1056
 notifier_call_chain kernel/notifier.c:87 [inline]
 blocking_notifier_call_chain+0x103/0x1b0 kernel/notifier.c:382

Memory state around the buggy address:
 ffff888026e8b080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888026e8b100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888026e8b180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                    ^
 ffff888026e8b200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888026e8b280: 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
2026/08/14 02:36 linux-6.1.y e4f7d8be268e b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/07/24 00:48 linux-6.1.y 090666d3cc90 544adce9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
* Struck through repros no longer work on HEAD.