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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+0x19fb/0x1d60 drivers/video/fbdev/core/sysimgblt.c:24
Write of size 8 at addr ffffc90003799000 by task syz.3.1658/13132

CPU: 0 UID: 0 PID: 13132 Comm: syz.3.1658 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x156/0x4c9 mm/kasan/report.c:482
 kasan_report+0xdf/0x1a0 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+0x19fb/0x1d60 drivers/video/fbdev/core/sysimgblt.c:24
 drm_fbdev_shmem_defio_imageblit+0x20/0x130 drivers/gpu/drm/drm_fbdev_shmem.c:39
 soft_cursor+0x524/0xa10 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0xe58/0x16f0 drivers/video/fbdev/core/bitblit.c:395
 fbcon_cursor+0x43c/0x5e0 drivers/video/fbdev/core/fbcon.c:1378
 hide_cursor+0x87/0x230 drivers/tty/vt/vt.c:855
 do_con_write+0x2403/0x8550 drivers/tty/vt/vt.c:3204
 con_put_char+0x73/0xa0 drivers/tty/vt/vt.c:3573
 tty_put_char+0xbe/0x160 drivers/tty/tty_io.c:3153
 n_tty_process_echo_ops drivers/tty/n_tty.c:643 [inline]
 __process_echoes+0x807/0xb10 drivers/tty/n_tty.c:689
 flush_echoes drivers/tty/n_tty.c:785 [inline]
 __receive_buf drivers/tty/n_tty.c:1618 [inline]
 n_tty_receive_buf_common+0x46a/0x1980 drivers/tty/n_tty.c:1715
 tiocsti drivers/tty/tty_io.c:2290 [inline]
 tty_ioctl+0x909/0x1690 drivers/tty/tty_io.c:2706
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc5a0d9aeb9
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:00007fc5a1bd9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc5a1016090 RCX: 00007fc5a0d9aeb9
RDX: 0000200000000e80 RSI: 0000000000005412 RDI: 0000000000000003
RBP: 00007fc5a0e08c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc5a1016128 R14: 00007fc5a1016090 R15: 00007ffcde51e058
 </TASK>

The buggy address belongs to a 0-page vmalloc region starting at 0xffffc90003499000 allocated at drm_gem_shmem_vmap_locked+0x54b/0x800 drivers/gpu/drm/drm_gem_shmem_helper.c:411
Memory state around the buggy address:
 ffffc90003798f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90003798f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc90003799000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90003799080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003799100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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