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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aa0e49877a2e Linux 6.6.148
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15e22bb9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=802bf88adfebfa7c354f
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/f83b390cfc1f/disk-aa0e4987.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1d4bdb338edd/vmlinux-aa0e4987.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3f57c1d51ee3/bzImage-aa0e4987.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+802bf8...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fast_imageblit drivers/video/fbdev/core/sysimgblt.c:257 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x1bac/0x25d0 drivers/video/fbdev/core/sysimgblt.c:323
Write of size 4 at addr ffffc90003d09fc0 by task syz.4.3141/20291

CPU: 1 PID: 20291 Comm: syz.4.3141 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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
fast_imageblit drivers/video/fbdev/core/sysimgblt.c:257 [inline]
sys_imageblit+0x1bac/0x25d0 drivers/video/fbdev/core/sysimgblt.c:323
drm_fbdev_generic_defio_imageblit+0x2c/0x110 drivers/gpu/drm/drm_fbdev_generic.c:37
cw_putcs_aligned drivers/video/fbdev/core/fbcon_cw.c:110 [inline]
cw_putcs+0x15f3/0x18a0 drivers/video/fbdev/core/fbcon_cw.c:158
fbcon_putcs+0x35c/0x520 drivers/video/fbdev/core/fbcon.c:1301
do_update_region+0x4e9/0x640 drivers/tty/vt/vt.c:623
redraw_screen+0xa30/0x1000 drivers/tty/vt/vt.c:983
vc_do_resize+0x1256/0x17f0 drivers/tty/vt/vt.c:1291
vt_resizex+0x3f0/0x5a0 drivers/tty/vt/vt_ioctl.c:718
vt_ioctl+0x1254/0x1f00 drivers/tty/vt/vt_ioctl.c:939
tty_ioctl+0x91e/0xdc0 drivers/tty/tty_io.c:2779
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f224c59e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f224d3d6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f224c826270 RCX: 00007f224c59e019
RDX: 00002000000006c0 RSI: 000000000000560a RDI: 0000000000000006
RBP: 00007f224c63500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f224c826308 R14: 00007f224c826270 R15: 00007ffc931eecd8
</TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
ffffc90003d09e80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90003d09f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003d09f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^
ffffc90003d0a000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90003d0a080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


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