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Date:   Sun, 17 Jan 2021 00:53:23 -0800
From:   syzbot <syzbot+b67aaae8d3a927f68d20@...kaller.appspotmail.com>
To:     b.zolnierkie@...sung.com, daniel.vetter@...ll.ch,
        dri-devel@...ts.freedesktop.org, george.kennedy@...cle.com,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        natechancellor@...il.com, sam@...nborg.org,
        syzkaller-bugs@...glegroups.com, yepeilin.cs@...il.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in fbcon_cursor

syzbot has found a reproducer for the following issue on:

HEAD commit:    b3a3cbde Add linux-next specific files for 20210115
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=164096d7500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6ea08dae6aab586f
dashboard link: https://syzkaller.appspot.com/bug?extid=b67aaae8d3a927f68d20
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15cd8fe0d00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17af5258d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b67aaae8d3a927f68d20@...kaller.appspotmail.com

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 12267067 P4D 12267067 PUD 11841067 PMD 0 
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8463 Comm: syz-executor088 Not tainted 5.11.0-rc3-next-20210115-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc9000132f850 EFLAGS: 00010292
RAX: 0000000000000007 RBX: 0000000000000000 RCX: 0000000000000007
RDX: 0000000000000002 RSI: ffff88814394b000 RDI: ffff888010071000
RBP: ffff888010071000 R08: 0000000000000000 R09: ffffffff83ed87ea
R10: 0000000000000003 R11: 0000000000000018 R12: ffff88814394b000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000720
FS:  0000000000db8880(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000020cd8000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 fbcon_cursor+0x50e/0x620 drivers/video/fbdev/core/fbcon.c:1336
 hide_cursor+0x85/0x280 drivers/tty/vt/vt.c:907
 redraw_screen+0x5b4/0x740 drivers/tty/vt/vt.c:1012
 vc_do_resize+0xed8/0x1150 drivers/tty/vt/vt.c:1325
 fbcon_set_disp+0x7a8/0xe10 drivers/video/fbdev/core/fbcon.c:1402
 con2fb_init_display drivers/video/fbdev/core/fbcon.c:808 [inline]
 set_con2fb_map+0x7a6/0xf80 drivers/video/fbdev/core/fbcon.c:879
 fbcon_set_con2fb_map_ioctl+0x165/0x220 drivers/video/fbdev/core/fbcon.c:3010
 do_fb_ioctl+0x5b6/0x690 drivers/video/fbdev/core/fbmem.c:1156
 fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1185
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4402b9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffffae24f88 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004402b9
RDX: 0000000020000080 RSI: 0000000000004610 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000246 R12: 0000000000401ac0
R13: 0000000000401b50 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 0000000000000000
---[ end trace 5adb9f198fe5efa6 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc9000132f850 EFLAGS: 00010292
RAX: 0000000000000007 RBX: 0000000000000000 RCX: 0000000000000007
RDX: 0000000000000002 RSI: ffff88814394b000 RDI: ffff888010071000
RBP: ffff888010071000 R08: 0000000000000000 R09: ffffffff83ed87ea
R10: 0000000000000003 R11: 0000000000000018 R12: ffff88814394b000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000720
FS:  0000000000db8880(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000020cd8000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

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