KASAN: null-ptr-deref Read in soft_cursor

[Dae R. Jeong]

Hi,

We observed an issue "KASAN: null-ptr-deref in soft_cursor" during fuzzing.

We acknowledge that this issue is a bit old, and we are sorry for
reporting this late. And unfortunately, we have not found a reproducer
for the crash yet. We will inform you if we have any update on this
crash.  Detailed crash information is attached below.

Best regards,
Dae R. Jeong

-----
- Kernel version:
6.2-rc1

- Crash report:
==================================================================
BUG: KASAN: null-ptr-deref in soft_cursor+0x420/0xe80 drivers/video/fbdev/core/softcursor.c:70
Read of size 16 at addr 0000000000000200 by task systemd/1

CPU: 2 PID: 1 Comm: systemd Not tainted 6.2.0-rc1-30092-gc55e2cce6a18-dirty #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1cf/0x2c0 lib/dump_stack.c:106
 print_report+0xed/0x1f0 mm/kasan/report.c:420
 kasan_report+0xef/0x120 mm/kasan/report.c:517
 kasan_check_range+0x2b5/0x2f0 mm/kasan/generic.c:189
 memcpy+0x25/0x60 mm/kasan/shadow.c:65
 soft_cursor+0x420/0xe80 drivers/video/fbdev/core/softcursor.c:70
 bit_cursor+0x1c95/0x2710 drivers/video/fbdev/core/bitblit.c:377
 hide_cursor+0x95/0x3f0 drivers/tty/vt/vt.c:907
 do_con_write+0x216/0xf270 drivers/tty/vt/vt.c:2927
 con_write+0x20/0x40 drivers/tty/vt/vt.c:3295
 process_output_block drivers/tty/n_tty.c:586 [inline]
 n_tty_write+0xef3/0x1420 drivers/tty/n_tty.c:2350
 do_tty_write drivers/tty/tty_io.c:1018 [inline]
 file_tty_write+0x625/0xa30 drivers/tty/tty_io.c:1089
 call_write_iter include/linux/fs.h:2186 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x848/0xd90 fs/read_write.c:584
 ksys_write+0x182/0x2c0 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4e/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fa7860101b0
Code: 2e 0f 1f 84 00 00 00 00 00 90 48 8b 05 19 7e 20 00 c3 0f 1f 84 00 00 00 00 00 83 3d 19 c2 20 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ae fc ff ff 48 89 04 24
RSP: 002b:00007ffea5a37dd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000000000a RCX: 00007fa7860101b0
RDX: 000000000000000a RSI: 00007fa78853ccbe RDI: 0000000000000013
RBP: 00007fa78853ccbe R08: 00007ffea5a37d90 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000013
R13: 0000000000000000 R14: ffffffffffffffff R15: 00005626fb929250
 </TASK>
==================================================================