KASAN: use-after-free Read in soft_cursor

Status: upstream: reported C repro on 2019/12/04 13:11
Reported-by: syzbot+f57ac5d99d8733e94387@syzkaller.appspotmail.com
First crash: 2446d, last: 1935d
Fix bisection the fix commit could be any of (bisect log):
  fbc5fe7a54d0 Linux 4.14.157
  56dfe6252c68 Linux 4.14.188
   
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: use-after-free Read in soft_cursor fbdev 19 syz, C done inconclusive 12 2168d 2444d 0/29 auto-obsoleted due to no activity on 2022/09/23 11:46
linux-4.19 KASAN: use-after-free Read in soft_cursor 19 syz, C done 16 2149d 2446d 1/1 fixed on 2020/10/26 21:28
linux-4.19 KASAN: use-after-free Read in soft_cursor (2) 19 2 2057d 2096d 0/1 auto-closed as invalid on 2021/04/26 05:01
linux-5.15 KASAN: null-ptr-deref Read in soft_cursor origin:lts-only 11 syz error 1 1175d 1176d 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 2 2d02h 23d 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 1911d 2033d 1/1 fixed on 2021/06/23 17:43
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1177d 1177d 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 1916d 2447d 0/1 upstream: reported C repro on 2019/12/03 14:54
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 194d 327d 0/29 auto-obsoleted due to no activity on 2026/05/14 02:42
upstream KASAN: global-out-of-bounds Read in soft_cursor (3) fbdev 19 21 49m 9d04h 22/29 upstream: reported on 2026/08/07 00:01
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 540d 536d 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 1909d 2376d 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 1435d 2435d 0/1 upstream: reported C repro on 2019/12/16 00:09
▶ ▼ Last patch testing requests (2)
Created Duration User Patch Repo Result
2023/02/07 11:32 10m retest repro linux-4.14.y report log
2022/09/16 21:29 11m retest repro linux-4.14.y report log
▶ ▼ Fix bisection attempts (5)
Created Duration User Patch Repo Result
2020/07/18 04:13 32m bisect fix linux-4.14.y OK (2) job log
2020/05/10 12:50 25m bisect fix linux-4.14.y OK (0) job log log
2020/04/10 12:25 24m bisect fix linux-4.14.y OK (0) job log log
2020/02/11 06:12 24m bisect fix linux-4.14.y OK (0) job log log
2020/01/12 05:47 24m bisect fix linux-4.14.y OK (0) job log log

Sample crash report:
audit: type=1400 audit(1575461251.847:36): avc:  denied  { map } for  pid=7015 comm="syz-executor252" path="/root/syz-executor252987772" dev="sda1" ino=16483 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: use-after-free in memcpy include/linux/string.h:347 [inline]
BUG: KASAN: use-after-free in soft_cursor+0x43d/0xa50 drivers/video/fbdev/core/softcursor.c:70
Read of size 9 at addr ffff88809f7e2e51 by task syz-executor252/7015

CPU: 1 PID: 7015 Comm: syz-executor252 Not tainted 4.14.157-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x142/0x197 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x123/0x190 mm/kasan/kasan.c:267
 memcpy+0x24/0x50 mm/kasan/kasan.c:302
 memcpy include/linux/string.h:347 [inline]
 soft_cursor+0x43d/0xa50 drivers/video/fbdev/core/softcursor.c:70
 bit_cursor+0x11be/0x1830 drivers/video/fbdev/core/bitblit.c:386
 fbcon_cursor+0x4e3/0x6f0 drivers/video/fbdev/core/fbcon.c:1347
 hide_cursor+0x9d/0x2e0 drivers/tty/vt/vt.c:589
 redraw_screen+0x2a5/0x7c0 drivers/tty/vt/vt.c:679
 vc_do_resize+0xc8a/0xec0 drivers/tty/vt/vt.c:954
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:974
 vt_ioctl+0x10a8/0x2170 drivers/tty/vt/vt_ioctl.c:901
 tty_ioctl+0x841/0x1320 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x440219
RSP: 002b:00007fff5036ec48 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440219
RDX: 00000000200002c0 RSI: 000000000000560a RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000001 R09: 00000000004002c8
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000401b00
R13: 0000000000401b90 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4051:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 kmem_cache_alloc_trace+0x152/0x790 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 alloc_pipe_info+0xb0/0x380 fs/pipe.c:647
 get_pipe_inode fs/pipe.c:726 [inline]
 create_pipe_files+0xc4/0x880 fs/pipe.c:759
 __do_pipe_flags+0x38/0x210 fs/pipe.c:816
 SYSC_pipe2 fs/pipe.c:864 [inline]
 SyS_pipe2 fs/pipe.c:858 [inline]
 SYSC_pipe fs/pipe.c:882 [inline]
 SyS_pipe+0x65/0x110 fs/pipe.c:880
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 4051:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcc/0x270 mm/slab.c:3815
 free_pipe_info+0x209/0x2b0 fs/pipe.c:698
 put_pipe_info+0xb3/0xd0 fs/pipe.c:575
 pipe_release+0x1b6/0x250 fs/pipe.c:596
 __fput+0x275/0x7a0 fs/file_table.c:210
 ____fput+0x16/0x20 fs/file_table.c:244
 task_work_run+0x114/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88809f7e2c80
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 465 bytes inside of
 512-byte region [ffff88809f7e2c80, ffff88809f7e2e80)
The buggy address belongs to the page:
page:ffffea00027df880 count:1 mapcount:0 mapping:ffff88809f7e2000 index:0x0
flags: 0xfffe0000000100(slab)
raw: 00fffe0000000100 ffff88809f7e2000 0000000000000000 0000000100000006
raw: ffffea00023b9b60 ffffea00024c1120 ffff8880aa800940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809f7e2d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809f7e2d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809f7e2e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88809f7e2e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809f7e2f00: 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
2019/12/04 12:10 linux-4.14.y fbc5fe7a54d0 0ecb9746 .config console log report syz C ci2-linux-4-14
2021/04/28 07:39 linux-4.14.y cf256fbcbe34 77e2b668 .config console log report info ci2-linux-4-14 KASAN: use-after-free Read in soft_cursor
2020/09/17 07:22 linux-4.14.y cbfa1702aaf6 8247808b .config console log report info ci2-linux-4-14
2020/06/18 02:58 linux-4.14.y b850307b279c d45a4d69 .config console log report ci2-linux-4-14
2020/05/23 23:33 linux-4.14.y a41ba30d9df2 96c92ad3 .config console log report ci2-linux-4-14
2020/03/11 11:46 linux-4.14.y 78d697fc93f9 e103bc9e .config console log report ci2-linux-4-14
2019/12/13 05:47 linux-4.14.y a844dc4c5442 2a752b7c .config console log report ci2-linux-4-14
* Struck through repros no longer work on HEAD.