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BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0xff5/0x1e40
Write of size 8 at addr ffffc900063e9000 by task syz.6.7270/23481

CPU: 0 UID: 0 PID: 23481 Comm: syz.6.7270 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_address_description+0x55/0x1e0
 print_report+0x58/0x70
 kasan_report+0x117/0x150
 sys_imageblit+0xff5/0x1e40
 drm_fbdev_shmem_defio_imageblit+0x2c/0x110
 soft_cursor+0xa0e/0xc40
 bit_cursor+0x11e5/0x19c0
 con_write+0x214/0x290
 do_output_char+0x656/0x970
 n_tty_write+0xdf2/0x11e0
 file_tty_write+0x509/0x9c0
 vfs_write+0x612/0xba0
 ksys_write+0x150/0x270
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f57f299e0d9
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:00007f57f38f5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f57f2c25fa0 RCX: 00007f57f299e0d9
RDX: 000000000000ffbc RSI: 00002000000011c0 RDI: 0000000000000003
RBP: 00007f57f2a35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f57f2c26038 R14: 00007f57f2c25fa0 R15: 00007ffc27fa4448
 </TASK>

The buggy address belongs to a 0-page vmalloc region starting at 0xffffc90006001000 allocated at drm_gem_shmem_vmap_locked+0x562/0x7d0
Memory state around the buggy address:
 ffffc900063e8f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc900063e8f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc900063e9000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc900063e9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900063e9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
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