linux-kernel - [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

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Message-ID: <6907c8c8.a70a0220.37351b.0012.GAE@google.com>
Date: Sun, 02 Nov 2025 13:10:32 -0800
From: syzbot <syzbot+5a40432dfe8f86ee657a@...kaller.appspotmail.com>
To: deller@....de, dri-devel@...ts.freedesktop.org, 
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org, simona@...ll.ch, 
	soci@....rulez.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

Hello,

syzbot found the following issue on:

HEAD commit:    691d401c7e0e Merge tag 'spi-fix-v6.18-rc3' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14607932580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=19d831c6d0386a9c
dashboard link: https://syzkaller.appspot.com/bug?extid=5a40432dfe8f86ee657a
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5eaccda03e4f/disk-691d401c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0df5294a69bc/vmlinux-691d401c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f4f242731772/bzImage-691d401c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5a40432dfe8f86ee657a@...kaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
Write of size 8 at addr ffffc90003e99280 by task kworker/0:2/781

CPU: 0 UID: 0 PID: 781 Comm: kworker/0:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events_power_efficient fb_flashcursor
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
 fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
 fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
 fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
 sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
 drm_fbdev_shmem_defio_imageblit+0x20/0x130 drivers/gpu/drm/drm_fbdev_shmem.c:38
 soft_cursor+0x524/0xa10 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0xe8c/0x17e0 drivers/video/fbdev/core/bitblit.c:395
 fb_flashcursor drivers/video/fbdev/core/fbcon.c:401 [inline]
 fb_flashcursor+0x310/0x400 drivers/video/fbdev/core/fbcon.c:370
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc90003e99180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003e99200: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003e99280: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90003e99300: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003e99380: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


---
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