[*] DF-2450 dm_pdev NULL-deref via non-block-device backing path
[*] Bug: dm_pdev_insert:168 dev_dioctl(v_rdev=NULL, DIOCGPART)
[*] Trigger: regular file as linear backing -> v_rdev NULL -> panic
[*] created regular file /tmp/df2450_backing (non-block-device vnode)
[*] create 'df2450dev': rv=0 (ok)
[*] reloading linear table with regular-file backing path...
[*] if claim is true: kernel panic in dev_dioctl (NULL v_rdev)
=== KERNEL PANICKED HERE -- ssh connection dropped ===
=== Guest down, panic signature from boot.log: ===

Fatal user address access from kernel mode from poc at ffffffff8062cd5c

Fatal trap 12: page fault while in kernel mode
cpuid = 1; lapic id = 1
fault virtual address	= 0xa8
fault code		= supervisor read data, page not present
instruction pointer	= 0x8:0xffffffff8062cd5c
stack pointer	        = 0x10:0xfffff801183f3478
frame pointer	        = 0x10:0xfffff801183f347d8
current process		= 864 (poc)
kernel: type 12 trap, code=0

Stopped at      dev_dioctl+0xc: movq    0xa8(%rdi),%rax
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