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

Status: upstream: reported on 2026/09/23 15:50
Reported-by: syzbot+e48502c72adccc4b4013@syzkaller.appspotmail.com
First crash: 1d10h, last: 1d10h
▶ ▼ Similar bugs (13)
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 30d 63d 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 1951d 2073d 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 1956d 2487d 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 2149d 2487d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 233d 367d 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 2177d 2486d 15/29 fixed on 2020/11/16 12:12
upstream KASAN: global-out-of-bounds Read in soft_cursor (3) fbdev 19 108 4h50m 49d 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 1215d 1216d 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 1975d 2486d 0/1 upstream: reported C repro on 2019/12/04 13:11
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1216d 1216d 22/29 fixed on 2023/07/01 16:05
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 580d 576d 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 1949d 2416d 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 1475d 2475d 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 52 at addr ffff88805575f398 by task syz.6.3390/15771

CPU: 0 PID: 15771 Comm: syz.6.3390 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 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
 ud_cursor+0x16c1/0x1fb0 drivers/video/fbdev/core/fbcon_ud.c:403
 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+0xc6e/0x1cd0 drivers/video/fbdev/core/fbcon.c:2411
 con_font_set drivers/tty/vt/vt.c:4669 [inline]
 con_font_op+0xace/0xdc0 drivers/tty/vt/vt.c:4715
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:476 [inline]
 vt_ioctl+0x1618/0x1ca0 drivers/tty/vt/vt_ioctl.c:754
 tty_ioctl+0x848/0xc30 drivers/tty/tty_io.c:2810
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fdedb7fd159
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:00007fded9a55028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fdedba84fa0 RCX: 00007fdedb7fd159
RDX: 0000200000000040 RSI: 0000000000004b72 RDI: 0000000000000004
RBP: 00007fdedb89406b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdedba85038 R14: 00007fdedba84fa0 R15: 00007ffc162ebdc8
 </TASK>

Allocated by task 8444:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kmalloc_array include/linux/slab.h:647 [inline]
 fbcon_rotate_font+0x3d2/0xdd0 drivers/video/fbdev/core/fbcon_rotate.c:53
 fbcon_switch+0xcad/0x2040 drivers/video/fbdev/core/fbcon.c:2118
 redraw_screen+0x581/0x1000 drivers/tty/vt/vt.c:1021
 fbcon_rotate_all drivers/video/fbdev/core/fbcon.c:240 [inline]
 store_rotate_all+0x423/0x510 drivers/video/fbdev/core/fbcon.c:3203
 kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2179 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88805575c000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 5016 bytes to the right of
 8192-byte region [ffff88805575c000, ffff88805575e000)
The buggy address belongs to the page:
page:ffffea000155d600 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888055758000 pfn:0x55758
head:ffffea000155d600 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001dd5c08 ffffea0001e0d608 ffff888016c42280
raw: ffff888055758000 0000000000020001 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 8440, ts 405028368891, free_ts 404710591210
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0xf9/0x290 mm/slub.c:3250
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 ppp_asynctty_open+0x91/0x560 drivers/net/ppp/ppp_async.c:165
 tty_ldisc_open drivers/tty/tty_ldisc.c:449 [inline]
 tty_set_ldisc+0x358/0x660 drivers/tty/tty_ldisc.c:579
 tty_ioctl+0xa8b/0xc30 drivers/tty/tty_io.c:2746
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x188/0x1e0 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xc0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x15d/0x280 mm/slub.c:3238
 __d_alloc+0x27/0x6d0 fs/dcache.c:1749
 d_alloc_anon fs/dcache.c:1849 [inline]
 d_alloc_cursor+0x40/0xd0 fs/dcache.c:1855
 dcache_dir_open+0x37/0x70 fs/libfs.c:82
 do_dentry_open+0x7f7/0xf90 fs/open.c:826
 do_open fs/namei.c:3659 [inline]
 path_openat+0x2718/0x2fb0 fs/namei.c:3793
 do_filp_open+0x1df/0x400 fs/namei.c:3820
 do_sys_openat2+0x14b/0x500 fs/open.c:1255

Memory state around the buggy address:
 ffff88805575f280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805575f300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805575f380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff88805575f400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805575f480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/23 15:50 linux-5.15.y 0248c33e835e abce1216 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in soft_cursor
* Struck through repros no longer work on HEAD.