KASAN: global-out-of-bounds Read in soft_cursor (3)

Status: upstream: reported on 2026/08/07 00:01
Subsystems: fbdev
[Documentation on labels]
Reported-by: syzbot+61b1db46218109869c14@syzkaller.appspotmail.com
Fix commit: e033cbf3975a fbdev: bitblit: bound-check glyph index in bit_cursor()
Patched on: [ci2-upstream-fs ci2-upstream-kcsan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-usb]
First crash: 54d, last: 15h59m
▶ ▼ ✨ AI Jobs (7)
ID Workflow Result Correct Bug Created Started Finished Revision
63db09da repro-c 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/08/07 14:02 2026/08/07 23:53 2026/08/07 23:53 e4ef95d6
7ad301e7 assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/07/20 00:02 2026/07/20 00:02 2026/07/20 00:22 72524a66
ec23ce0a assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/07/04 00:02 2026/07/04 00:02 2026/07/04 00:22 93f57954
8bd68c83 assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/06/26 00:01 2026/06/26 00:01 2026/06/26 00:01 7ff32d8b
0bdf31f6 assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/06/21 00:03 2026/06/21 00:03 2026/06/21 00:03 43bfcdb0
c5eb2494 assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/06/18 08:47 2026/06/18 08:47 2026/06/18 08:47 b62b3ded
be8f3004 assessment-security 💥 KASAN: global-out-of-bounds Read in soft_cursor (3) 2026/06/17 00:03 2026/06/17 00:03 2026/06/17 00:03 0e4b3e40
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH] fbdev: bitblit: bound-check glyph index in bit_cursor() 2 (2) 2026/08/08 05:44
[syzbot] [fbdev?] KASAN: global-out-of-bounds Read in soft_cursor (3) 0 (1) 2026/08/07 00:01
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 186d 320d 0/29 auto-obsoleted due to no activity on 2026/05/14 02:42
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 532d 528d 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 1901d 2368d 1/1 fixed on 2021/06/24 08:01
upstream KASAN: global-out-of-bounds Read in soft_cursor fbdev 17 11 2205d 2431d 0/29 auto-closed as invalid on 2020/11/22 03:01
linux-4.14 KASAN: global-out-of-bounds Read in soft_cursor 17 syz, C error 19 1428d 2427d 0/1 upstream: reported C repro on 2019/12/16 00:09
linux-5.15 KASAN: null-ptr-deref Read in soft_cursor origin:lts-only 11 syz error 1 1168d 1168d 0/3 auto-obsoleted due to no activity on 2024/12/24 15:39
linux-6.1 KASAN: slab-out-of-bounds Read in soft_cursor 17 1 15d 15d 0/3 upstream: reported on 2026/07/24 00:48
linux-4.14 KASAN: use-after-free Read in soft_cursor 19 syz, C inconclusive 7 1928d 2439d 0/1 upstream: reported C repro on 2019/12/04 13:11
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor (2) 17 syz, C done 8 1904d 2026d 1/1 fixed on 2021/06/23 17:43
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1169d 1169d 22/29 fixed on 2023/07/01 16:05
linux-4.14 KASAN: slab-out-of-bounds Read in soft_cursor 17 syz, C unreliable 57 1909d 2440d 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 2102d 2440d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor fbdev 17 syz, C done 218 2130d 2439d 15/29 fixed on 2020/11/16 12:12

Sample crash report:
==================================================================
BUG: KASAN: global-out-of-bounds in soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70
Read of size 16 at addr ffff800086c57970 by task syz.7.609/8216

CPU: 0 UID: 0 PID: 8216 Comm: syz.7.609 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xb0/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0x8c/0xc4 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x17c/0x1ac mm/kasan/generic.c:200
 __asan_memcpy+0x3c/0x84 mm/kasan/shadow.c:105
 soft_cursor+0x378/0x6bc drivers/video/fbdev/core/softcursor.c:70
 bit_cursor+0xa90/0x1108 drivers/video/fbdev/core/bitblit.c:365
 fbcon_cursor+0x344/0x498 drivers/video/fbdev/core/fbcon.c:1427
 hide_cursor+0xdc/0x2d0 drivers/tty/vt/vt.c:883
 update_region+0x100/0x18c drivers/tty/vt/vt.c:669
 vcs_write+0x8ec/0xaf0 drivers/tty/vt/vc_screen.c:685
 do_loop_readv_writev+0x24c/0x3dc fs/read_write.c:-1
 vfs_writev+0x2c8/0x630 fs/read_write.c:1061
 do_writev+0x134/0x2a8 fs/read_write.c:1105
 __do_sys_writev fs/read_write.c:1173 [inline]
 __se_sys_writev fs/read_write.c:1170 [inline]
 __arm64_sys_writev+0x80/0x94 fs/read_write.c:1170
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

The buggy address belongs to the variable:
 fontdata_8x16+0x1010/0x1480

The buggy address belongs to a vmalloc virtual mapping
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x219857
flags: 0x5ffc00000002000(reserved|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000002000 fffffdffc76615c8 fffffdffc76615c8 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff800086c57800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff800086c57880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff800086c57900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f9 f9
                                                             ^
 ffff800086c57980: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
 ffff800086c57a00: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
==================================================================

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/15 17:15 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci c2a9495bd873 50bb0618 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: global-out-of-bounds Read in soft_cursor
2026/08/07 01:45 upstream fcaeecb8b0cd c38879ea .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/05 13:32 upstream c21bb4193868 1eed00d1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/04 23:32 upstream 562bfb501c54 52aa2820 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/08 02:56 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci ba5cc80fd326 e4ef95d6 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/07 07:30 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci db788396cbb1 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/06 16:56 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 7235a3e71949 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/05 19:05 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 7235a3e71949 b3eac40e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: slab-use-after-free Read in soft_cursor
* Struck through repros no longer work on HEAD.