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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:22
Write of size 8 at addr ffffc90005021000 by task syz.3.387/7376

CPU: 2 UID: 0 PID: 7376 Comm: syz.3.387 Not tainted 6.16.0-rc3-syzkaller-00042-g78f4e737a53e #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
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:408 [inline]
 print_report+0xcd/0x680 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 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:22
 drm_fbdev_shmem_defio_imageblit+0x20/0x130 drivers/gpu/drm/drm_fbdev_shmem.c:37
 bit_putcs_unaligned drivers/video/fbdev/core/bitblit.c:138 [inline]
 bit_putcs+0x90f/0xde0 drivers/video/fbdev/core/bitblit.c:187
 fbcon_putcs+0x383/0x4a0 drivers/video/fbdev/core/fbcon.c:1314
 do_update_region+0x2e6/0x3f0 drivers/tty/vt/vt.c:627
 redraw_screen+0x63f/0x760 drivers/tty/vt/vt.c:979
 fbcon_set_disp+0x7d4/0xe40 drivers/video/fbdev/core/fbcon.c:1418
 con2fb_init_display drivers/video/fbdev/core/fbcon.c:816 [inline]
 set_con2fb_map+0x703/0x1060 drivers/video/fbdev/core/fbcon.c:889
 fbcon_set_con2fb_map_ioctl+0x16c/0x220 drivers/video/fbdev/core/fbcon.c:3118
 do_fb_ioctl+0x328/0x7e0 drivers/video/fbdev/core/fb_chrdev.c:138
 fb_ioctl+0xe5/0x150 drivers/video/fbdev/core/fb_chrdev.c:169
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl fs/ioctl.c:893 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f268938e929
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:00007f268a207038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f26895b6080 RCX: 00007f268938e929
RDX: 0000200000000180 RSI: 0000000000004610 RDI: 0000000000000003
RBP: 00007f2689410b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f26895b6080 R15: 00007ffff05734a8
 </TASK>

The buggy address belongs to the virtual mapping at
 [ffffc90004d21000, ffffc90005022000) created by:
 drm_gem_shmem_vmap_locked+0x4bc/0x720 drivers/gpu/drm/drm_gem_shmem_helper.c:369

Memory state around the buggy address:
 ffffc90005020f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90005020f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc90005021000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90005021080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90005021100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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