bisecting fixing commit since 830a059cbba6832c11fefc0894c7ec7a27f75734
building syzkaller on 6a81331a1d4c744da9204d02ec88d558f7eea9c9
testing commit 830a059cbba6832c11fefc0894c7ec7a27f75734 with gcc (GCC) 8.4.1 20210217
kernel signature: 6b4952966599e3ece9a7b56a06397c76cefe0266f0e99d17c89660faf14eba2d
all runs: crashed: KASAN: slab-out-of-bounds Read in soft_cursor
testing current HEAD 3c8c23092588a23bf1856a64f58c37f477a413be
testing commit 3c8c23092588a23bf1856a64f58c37f477a413be with gcc (GCC) 8.4.1 20210217
kernel signature: 678fc8a8cf8977dca5a9072a902b38f4ceb645465d05212dbf97fb771cc7d400
all runs: crashed: KASAN: slab-out-of-bounds Read in soft_cursor
revisions tested: 2, total time: 28m49.283702318s (build: 17m50.166901242s, test: 10m31.528896485s)
the crash still happens on HEAD
commit msg: Linux 4.19.190
crash: KASAN: slab-out-of-bounds Read in soft_cursor
ieee802154 phy1 wpan1: encryption failed: -22
==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:377 [inline]
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x430/0xc70 drivers/video/fbdev/core/softcursor.c:70
Read of size 15 at addr ffff88809dacb230 by task kworker/0:4/9696

CPU: 0 PID: 9696 Comm: kworker/0:4 Not tainted 4.19.190-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_power_efficient fb_flashcursor
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x17c/0x226 lib/dump_stack.c:118
 print_address_description.cold.6+0x9/0x211 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report mm/kasan/report.c:412 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:396
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13c/0x1b0 mm/kasan/kasan.c:267
 memcpy+0x23/0x50 mm/kasan/kasan.c:302
 memcpy include/linux/string.h:377 [inline]
 soft_cursor+0x430/0xc70 drivers/video/fbdev/core/softcursor.c:70
 bit_cursor+0xdca/0x1d40 drivers/video/fbdev/core/bitblit.c:377
 fb_flashcursor+0x31e/0x3c0 drivers/video/fbdev/core/fbcon.c:379
 process_one_work+0x7b9/0x15a0 kernel/workqueue.c:2152
 worker_thread+0x85/0xb60 kernel/workqueue.c:2295
 kthread+0x347/0x410 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 9903:
 save_stack mm/kasan/kasan.c:448 [inline]
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:553
 kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:538
 __do_kmalloc mm/slab.c:3727 [inline]
 __kmalloc+0x15d/0x3d0 mm/slab.c:3736
 kmalloc include/linux/slab.h:520 [inline]
 fbcon_set_font+0x2cd/0x800 drivers/video/fbdev/core/fbcon.c:2482
 con_font_set drivers/tty/vt/vt.c:4537 [inline]
 con_font_op+0xb79/0x11d0 drivers/tty/vt/vt.c:4581
 do_fontx_ioctl drivers/tty/vt/vt_ioctl.c:265 [inline]
 vt_ioctl+0xff0/0x2200 drivers/tty/vt/vt_ioctl.c:955
 tty_ioctl+0x456/0x1290 drivers/tty/tty_io.c:2669
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688
 ksys_ioctl+0x62/0x90 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff88809dacb040
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 496 bytes inside of
 512-byte region [ffff88809dacb040, ffff88809dacb240)
The buggy address belongs to the page:
page:ffffea000276b2c0 count:1 mapcount:0 mapping:ffff88813bff6940 index:0xffff88809dacba40
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffffea0002d48208 ffffea0002715dc8 ffff88813bff6940
raw: ffff88809dacba40 ffff88809dacb040 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809dacb100: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
 ffff88809dacb180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88809dacb200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                     ^
 ffff88809dacb280: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff88809dacb300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================