[v6.6] KASAN: vmalloc-out-of-bounds Write in drm_fbdev_generic_helper_fb_dirty

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6436c12a2ced Linux 6.6.150
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=176ebe49580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=aa4beb6f1c501d592d09
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f01168de2d4b/disk-6436c12a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e63b80c9c349/vmlinux-6436c12a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9297ad58728c/bzImage-6436c12a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aa4beb...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in iosys_map_memcpy_to include/linux/iosys-map.h:287 [inline]
BUG: KASAN: vmalloc-out-of-bounds in drm_fbdev_generic_damage_blit_real drivers/gpu/drm/drm_fbdev_generic.c:173 [inline]
BUG: KASAN: vmalloc-out-of-bounds in drm_fbdev_generic_damage_blit drivers/gpu/drm/drm_fbdev_generic.c:204 [inline]
BUG: KASAN: vmalloc-out-of-bounds in drm_fbdev_generic_helper_fb_dirty+0x57e/0xab0 drivers/gpu/drm/drm_fbdev_generic.c:224
Write of size 32 at addr ffffc900040128a0 by task kworker/1:2/789

CPU: 1 PID: 789 Comm: kworker/1:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events drm_fb_helper_damage_work
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
__asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
iosys_map_memcpy_to include/linux/iosys-map.h:287 [inline]
drm_fbdev_generic_damage_blit_real drivers/gpu/drm/drm_fbdev_generic.c:173 [inline]
drm_fbdev_generic_damage_blit drivers/gpu/drm/drm_fbdev_generic.c:204 [inline]
drm_fbdev_generic_helper_fb_dirty+0x57e/0xab0 drivers/gpu/drm/drm_fbdev_generic.c:224
drm_fb_helper_fb_dirty drivers/gpu/drm/drm_fb_helper.c:388 [inline]
drm_fb_helper_damage_work+0x22f/0x6f0 drivers/gpu/drm/drm_fb_helper.c:411
process_one_work kernel/workqueue.c:2657 [inline]
process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
ffffc90004012780: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90004012800: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90004012880: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^
ffffc90004012900: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90004012980: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


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