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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 ffffc900038c9000 by task syz.1.1754/14992

CPU: 0 UID: 0 PID: 14992 Comm: syz.1.1754 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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+0x521/0xa10 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0xe8c/0x17e0 drivers/video/fbdev/core/bitblit.c:370
 fbcon_cursor+0x40c/0x5f0 drivers/video/fbdev/core/fbcon.c:1362
 set_cursor drivers/tty/vt/vt.c:867 [inline]
 set_cursor+0x1d8/0x250 drivers/tty/vt/vt.c:858
 con_flush_chars drivers/tty/vt/vt.c:3586 [inline]
 con_write+0x89/0xb0 drivers/tty/vt/vt.c:3517
 do_output_char+0x5d9/0x840 drivers/tty/n_tty.c:422
 process_output drivers/tty/n_tty.c:486 [inline]
 n_tty_write+0x4ff/0x11e0 drivers/tty/n_tty.c:2388
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write.constprop.0+0x504/0x9b0 drivers/tty/tty_io.c:1081
 tty_write drivers/tty/tty_io.c:1102 [inline]
 redirected_tty_write drivers/tty/tty_io.c:1125 [inline]
 redirected_tty_write+0xd4/0x150 drivers/tty/tty_io.c:1105
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d0/0x11d0 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbc2d38ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbc2e1fa038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fbc2d5c6180 RCX: 00007fbc2d38ebe9
RDX: 00000000000009e5 RSI: 0000200000000e00 RDI: 000000000000000d
RBP: 00007fbc2d411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbc2d5c6218 R14: 00007fbc2d5c6180 R15: 00007ffd78bc3898
 </TASK>

The buggy address belongs to a 0-page vmalloc region starting at 0xffffc900035c9000 allocated at drm_gem_shmem_vmap_locked+0x561/0x7e0 drivers/gpu/drm/drm_gem_shmem_helper.c:371
Memory state around the buggy address:
 ffffc900038c8f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc900038c8f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900038c9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc900038c9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900038c9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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