bin/56691: newfs_v7fs bus error when passed vnd0d

[abs%absd.org@localhost]

>Number:         56691
>Category:       bin
>Synopsis:       newfs_v7fs bus error when passed vnd0d
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 05 22:15:00 +0000 2022
>Originator:     David Brownlee
>Release:        NetBSD 9.99.92
>Organization:
none
>Environment:
NetBSD forsaken.absd.org 9.99.92 NetBSD 9.99.92 (GENERIC) #0: Mon Jan 24 16:56:26 GMT 2022  abs%iris.absd.org@localhost:/home/netbsd/src/sys/arch/amd64/compile/obj/GENERIC amd64

>Description:
Attempting to use newfs_v7fs to newfs a vnd0 partition exits with a bus error. Running the same command on the raw file completes without issue

>How-To-Repeat:
       dd if=/dev/zero of=/tmp/fs bs=1m count=100
        vndconfig vnd0 /dev/fs
        newfs_v7fs -V 4 -F -s 65536 /dev/vnd0d
        volume size=65536, ilist size=2621, endian=1234, NAME_MAX=14
        zsh: bus error

#0  0x00007d4d16b6cc14 in memcpy () from /lib/libc.so.12
#1  0x00000001ba803d59 in read_mmap (ctx=<optimized out>, buf=<optimized out>, sector=<optimized out>) at .../src/sys/fs/v7fs/v7fs_io_user.c:158
#2  0x00000001ba803ce9 in scratch_read (fs=fs@entry=0x7d4d17223000, blk=blk@entry=1) at .../src/sys/fs/v7fs/v7fs_io.c:97
#3  0x00000001ba8020b3 in v7fs_superblock_load (fs=fs@entry=0x7d4d17223000) at .../src/sys/fs/v7fs/v7fs_superblock.c:78
#4  0x00000001ba801b7b in partition_check (fs=0x7d4d17223000) at .../src/sbin/newfs_v7fs/main.c:81
#5  v7fs_newfs (mount=<optimized out>, maxfile=0) at .../src/sbin/newfs_v7fs/main.c:299
#6  0x00000001ba8044d2 in main (argc=<optimized out>, argv=<optimized out>) at .../src/sbin/newfs_v7fs/newfs_v7fs.c:194

>Fix: