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Date:      Mon, 08 Oct 2018 01:07:16 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 232021] zfs cannot mount 'dataset': Insufficient privileges
Message-ID:  <bug-232021-227-8jrPP64Vgo@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-232021-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-232021-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D232021

--- Comment #12 from Allan Jude <allanjude@FreeBSD.org> ---
After investigating further, I am a bit torn on this one.

Rules that apply to mounting:

if vfs.usermount =3D=3D 1, user must own the directory they are attempting =
to mount
to

https://svnweb.freebsd.org/base/head/sys/kern/vfs_mount.c?view=3Dmarkup#l855

Rules that apply to unmounting:

if vfs.usermount =3D=3D 1, user must be the one who mounted the filesystem

UNLESS the filesystem has the VFCF_DELEGADMIN flag (which ZFS does), in whi=
ch
case the 'who did the mounting' check is bypassed.=20

https://svnweb.freebsd.org/base/head/sys/kern/vfs_subr.c?view=3Dmarkup#l718


So, ZFS has an exception to the vfs.usermount rule for unmounting. The kern=
el
allows ZFS to implement its own checks (zfs allow mount) to determine if the
umount operation should succeed.

This feels oddly asymmetrical to me, although I see the additional security
considerations for mounting, vs umounting.

Making the vfs.usermount 'who did the mounting' check apply feels like a
regression against the administrators expressed intent with 'zfs allow moun=
t'
on the target filesystem.

So it may be the case that we just need to document this as the intended
behaviour.

--=20
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