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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 ffffc900040c9000 by task syz.2.1753/10595

CPU: 1 PID: 10595 Comm: syz.2.1753 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
 soft_cursor+0xa01/0xc30 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0x16b2/0x1f10 drivers/video/fbdev/core/bitblit.c:404
 set_cursor drivers/tty/vt/vt.c:868 [inline]
 con_flush_chars+0x1fa/0x280 drivers/tty/vt/vt.c:3318
 con_write+0x2e/0x40 drivers/tty/vt/vt.c:3246
 do_output_char+0x64a/0x960 drivers/tty/n_tty.c:433
 __process_echoes+0x2e0/0x9f0 drivers/tty/n_tty.c:723
 flush_echoes drivers/tty/n_tty.c:813 [inline]
 __receive_buf drivers/tty/n_tty.c:1648 [inline]
 n_tty_receive_buf_common+0xc81/0x1380 drivers/tty/n_tty.c:1745
 paste_selection+0x329/0x4d0 drivers/tty/vt/selection.c:409
 vt_ioctl+0x813/0x1f00 drivers/tty/vt/vt_ioctl.c:762
 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: 0033:0x7f4a5599e0d9
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:00007f4a568ee028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f4a55c25fa0 RCX: 00007f4a5599e0d9
RDX: 0000200000000000 RSI: 000000000000541c RDI: 0000000000000005
RBP: 00007f4a55a35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4a55c26038 R14: 00007f4a55c25fa0 R15: 00007ffec4bedf28
 </TASK>

The buggy address belongs to a 768-page vmalloc region starting at 0xffffc90003dc9000 allocated at drm_fbdev_generic_helper_fb_probe+0x247/0x520 drivers/gpu/drm/drm_fbdev_generic.c:97
Memory state around the buggy address:
 ffffc900040c8f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc900040c8f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900040c9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc900040c9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900040c9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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