[syzbot] BUG: unable to handle kernel NULL pointer dereference in fbcon_putcs

[syzbot] BUG: unable to handle kernel NULL pointer dereference in fbcon_putcs

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f88cd3fb Merge tag 'vfio-v5.13-rc5' of git://github.com/aw..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126f13b0300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ad5040c83f09b8e4
dashboard link: https://syzkaller.appspot.com/bug?extid=4e611f0926f7122c8d34
compiler:       Debian clang version 11.0.1-2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4e611f0926f7122c8d34@syzkaller.appspotmail.com

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 2cdec067 P4D 2cdec067 PUD 2937a067 PMD 0 
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 15551 Comm: syz-executor.1 Not tainted 5.13.0-rc4-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:ffffc90001bcf630 EFLAGS: 00010292
RAX: 0000000000000000 RBX: ffff88801f456000 RCX: 000000000000004e
RDX: ffff88801dc61224 RSI: ffff88801f456000 RDI: ffff888011879000
RBP: 1ffff11003b8c244 R08: 000000000000001d R09: 0000000000000002
R10: 0000000000000002 R11: ffff888037fb9c40 R12: ffff88801dc61224
R13: dffffc0000000000 R14: 000000000000001d R15: ffff888011879000
FS:  00007f7816197700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000022965000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 fbcon_putcs+0x2ae/0x430 drivers/video/fbdev/core/fbcon.c:1296
 do_update_region+0x4d6/0x6a0 drivers/tty/vt/vt.c:676
 invert_screen+0xc03/0xe30 drivers/tty/vt/vt.c:800
 highlight drivers/tty/vt/selection.c:57 [inline]
 clear_selection+0x55/0x70 drivers/tty/vt/selection.c:84
 vc_do_resize+0x6d6/0x1890 drivers/tty/vt/vt.c:1240
 fbcon_set_disp+0x9f2/0xf90 drivers/video/fbdev/core/fbcon.c:1405
 con2fb_init_display drivers/video/fbdev/core/fbcon.c:808 [inline]
 set_con2fb_map+0x7f6/0xe90 drivers/video/fbdev/core/fbcon.c:879
 fbcon_set_con2fb_map_ioctl+0x1e7/0x300 drivers/video/fbdev/core/fbcon.c:3013
 do_fb_ioctl+0x39c/0x7e0 drivers/video/fbdev/core/fbmem.c:1156
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7816197188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9
RDX: 0000000020000000 RSI: 0000000000004610 RDI: 0000000000000003
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffe47f399af R14: 00007f7816197300 R15: 0000000000022000
Modules linked in:
CR2: 0000000000000000
---[ end trace 1eae45a248f50072 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc90001bcf630 EFLAGS: 00010292
RAX: 0000000000000000 RBX: ffff88801f456000 RCX: 000000000000004e
RDX: ffff88801dc61224 RSI: ffff88801f456000 RDI: ffff888011879000
RBP: 1ffff11003b8c244 R08: 000000000000001d R09: 0000000000000002
R10: 0000000000000002 R11: ffff888037fb9c40 R12: ffff88801dc61224
R13: dffffc0000000000 R14: 000000000000001d R15: ffff888011879000
FS:  00007f7816197700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 0000000022965000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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Re: [syzbot] BUG: unable to handle kernel NULL pointer dereference in fbcon_putcs

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: BUG: unable to handle kernel NULL pointer dereference in fbcon_putcs
Author: qianqiang.liu@163.com

#syz test

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 3f7333dca508..96c1262cc981 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
 	struct fbcon_display *p = &fb_display[vc->vc_num];
 	struct fbcon_ops *ops = info->fbcon_par;
 
-	if (!fbcon_is_inactive(vc, info))
+	if (!fbcon_is_inactive(vc, info) && ops->putcs)
 		ops->putcs(vc, info, s, count, real_y(p, ypos), xpos,
 			   get_color(vc, info, scr_readw(s), 1),
 			   get_color(vc, info, scr_readw(s), 0));

-- 
Best,
Qianqiang Liu