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

[syzbot]

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+5a4043...@syzkaller.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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