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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 ffffc900039290a0 by task syz.5.2845/19726

CPU: 0 UID: 0 PID: 19726 Comm: syz.5.2845 Tainted: G     U              6.15.0-rc5-syzkaller-00123-g2c89c1b655c0 #0 PREEMPT(full) 
Tainted: [U]=USER
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/29/2025
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:408 [inline]
 print_report+0xc3/0x670 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
 soft_cursor+0x521/0xa10 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0xe8c/0x17e0 drivers/video/fbdev/core/bitblit.c:370
 fbcon_cursor+0x409/0x5f0 drivers/video/fbdev/core/fbcon.c:1344
 hide_cursor+0x84/0x220 drivers/tty/vt/vt.c:846
 do_con_write+0x219b/0x7c90 drivers/tty/vt/vt.c:3068
 con_put_char+0x73/0xa0 drivers/tty/vt/vt.c:3440
 tty_put_char+0xbb/0x160 drivers/tty/tty_io.c:3166
 do_output_char+0x151/0x840 drivers/tty/n_tty.c:463
 process_output drivers/tty/n_tty.c:486 [inline]
 n_tty_write+0x4cd/0x1160 drivers/tty/n_tty.c:2388
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write.constprop.0+0x4ff/0x9b0 drivers/tty/tty_io.c:1090
 tty_write drivers/tty/tty_io.c:1111 [inline]
 redirected_tty_write drivers/tty/tty_io.c:1134 [inline]
 redirected_tty_write+0xd4/0x150 drivers/tty/tty_io.c:1114
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x5ba/0x1180 fs/read_write.c:684
 ksys_write+0x12a/0x240 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3f9b98e969
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:00007f3f9c800038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f3f9bbb6080 RCX: 00007f3f9b98e969
RDX: 0000000000000d8e RSI: 0000200000000e00 RDI: 0000000000000002
RBP: 00007f3f9ba10ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f3f9bbb6080 R15: 00007ffd3b57c5c8
 </TASK>

The buggy address belongs to the virtual mapping at
 [ffffc90003629000, ffffc9000392a000) created by:
 drm_gem_shmem_vmap+0x3fa/0x750 drivers/gpu/drm/drm_gem_shmem_helper.c:365

Memory state around the buggy address:
 ffffc90003928f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90003929000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003929080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                               ^
 ffffc90003929100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003929180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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