CVS commit: src/sys

["Juergen Hannken-Illjes" <hannken%netbsd.org@localhost>]

Module Name:    src
Committed By:   hannken
Date:           Fri Dec  9 10:33:18 UTC 2022

Modified Files:
        src/sys/kern: vfs_mount.c
        src/sys/miscfs/genfs: layer_vfsops.c

Log Message:
Harden layered file systems usage of field "mnt_lower" against
forced unmounts of the lower layer.

- Dont allow "dead_rootmount" as lower layer.

- Take file system busy before a vfs operation walks down the stack.

Reported-by: syzbot+27b35e5675b1753cec03%syzkaller.appspotmail.com@localhost
Reported-by: syzbot+99071492e3de2eff49e9%syzkaller.appspotmail.com@localhost


To generate a diff of this commit:
cvs rdiff -u -r1.100 -r1.101 src/sys/kern/vfs_mount.c
cvs rdiff -u -r1.55 -r1.56 src/sys/miscfs/genfs/layer_vfsops.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.