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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+0x1ba8/0x25d0 drivers/video/fbdev/core/sysimgblt.c:323
Write of size 4 at addr ffffc900048c9000 by task syz.3.3502/17983

CPU: 1 PID: 17983 Comm: syz.3.3502 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 fast_imageblit drivers/video/fbdev/core/sysimgblt.c:257 [inline]
 sys_imageblit+0x1ba8/0x25d0 drivers/video/fbdev/core/sysimgblt.c:323
 drm_fb_helper_sys_imageblit+0x2e/0x510 drivers/gpu/drm/drm_fb_helper.c:864
 soft_cursor+0x9fd/0xc30 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0x16b5/0x1f40 drivers/video/fbdev/core/bitblit.c:409
 set_cursor drivers/tty/vt/vt.c:920 [inline]
 con_flush_chars+0x1f6/0x270 drivers/tty/vt/vt.c:3368
 con_write+0x29/0x40 drivers/tty/vt/vt.c:3296
 do_output_char+0x58a/0x960 drivers/tty/n_tty.c:440
 __process_echoes+0x2a2/0x8f0 drivers/tty/n_tty.c:727
 commit_echoes drivers/tty/n_tty.c:782 [inline]
 n_tty_receive_char+0x811/0xbb0 drivers/tty/n_tty.c:1420
 n_tty_receive_buf_standard+0x5fb/0x4d90 drivers/tty/n_tty.c:1589
 __receive_buf drivers/tty/n_tty.c:1623 [inline]
 n_tty_receive_buf_common+0xc08/0x1470 drivers/tty/n_tty.c:1721
 paste_selection+0x321/0x4c0 drivers/tty/vt/selection.c:409
 vt_ioctl+0x441/0x1ca0 drivers/tty/vt/vt_ioctl.c:764
 tty_ioctl+0x7e6/0xba0 drivers/tty/tty_io.c:2776
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc3ad59e0d9
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:00007fc3ae3c7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc3ad826180 RCX: 00007fc3ad59e0d9
RDX: 00002000000002c0 RSI: 000000000000541c RDI: 0000000000000008
RBP: 00007fc3ad635024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc3ad826218 R14: 00007fc3ad826180 R15: 00007ffdbc3dcde8
 </TASK>

The buggy address belongs to a 0-page vmalloc region starting at 0xffffc900045c9000 allocated at drm_gem_shmem_vmap_locked drivers/gpu/drm/drm_gem_shmem_helper.c:320 [inline]
The buggy address belongs to a 0-page vmalloc region starting at 0xffffc900045c9000 allocated at drm_gem_shmem_vmap+0x347/0x4d0 drivers/gpu/drm/drm_gem_shmem_helper.c:367
Memory state around the buggy address:
 ffffc900048c8f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc900048c8f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900048c9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc900048c9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900048c9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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