svn commit: r333263 - in head: lib/libjail sys/cddl/contrib/opensolaris/uts/common/fs/zfs sys/compat/linprocfs sys/compat/linsysfs sys/fs/devfs sys/fs/fdescfs sys/fs/nullfs sys/fs/procfs sys/fs/pse...

[Alan Somers]

On Fri, Nov 16, 2018 at 2:28 PM James Gritton <jamie at freebsd.org> wrote:

> On 2018-11-16 10:34, Alan Somers wrote:
>
> On Fri, May 4, 2018 at 2:54 PM Jamie Gritton <jamie at freebsd.org> wrote:
>
>> Author: jamie
>> Date: Fri May  4 20:54:27 2018
>> New Revision: 333263
>> URL: https://svnweb.freebsd.org/changeset/base/333263
>>
>> Log:
>>   Make it easier for filesystems to count themselves as jail-enabled,
>>   by doing most of the work in a new function prison_add_vfs in
>> kern_jail.c
>>   Now a jail-enabled filesystem need only mark itself with VFCF_JAIL, and
>>   the rest is taken care of.  This includes adding a jail parameter like
>>   allow.mount.foofs, and a sysctl like security.jail.mount_foofs_allowed.
>>   Both of these used to be a static list of known filesystems, with
>>   predefined permission bits.
>>
>>   Reviewed by:  kib
>>   Differential Revision:        D14681
>>
>> Modified:
>>   head/lib/libjail/jail.c
>>   head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
>>   head/sys/compat/linprocfs/linprocfs.c
>>   head/sys/compat/linsysfs/linsysfs.c
>>   head/sys/fs/devfs/devfs_vfsops.c
>>   head/sys/fs/fdescfs/fdesc_vfsops.c
>>   head/sys/fs/nullfs/null_vfsops.c
>>   head/sys/fs/procfs/procfs.c
>>   head/sys/fs/pseudofs/pseudofs.h
>>   head/sys/fs/tmpfs/tmpfs_vfsops.c
>>   head/sys/kern/kern_jail.c
>>   head/sys/kern/vfs_init.c
>>   head/sys/kern/vfs_mount.c
>>   head/sys/kern/vfs_subr.c
>>   head/sys/sys/jail.h
>>   head/sys/sys/mount.h
>>   head/usr.sbin/jail/jail.8
>>
>> Modified: head/lib/libjail/jail.c
>>
>> ==============================================================================
>> --- head/lib/libjail/jail.c     Fri May  4 20:38:26 2018        (r333262)
>> +++ head/lib/libjail/jail.c     Fri May  4 20:54:27 2018        (r333263)
>> @@ -1048,7 +1048,13 @@ kldload_param(const char *name)
>>         else if (strcmp(name, "sysvmsg") == 0 || strcmp(name, "sysvsem")
>> == 0 ||
>>             strcmp(name, "sysvshm") == 0)
>>                 kl = kldload(name);
>> -       else {
>> +       else if (strncmp(name, "allow.mount.", 12) == 0) {
>> +               /* Load the matching filesystem */
>> +               kl = kldload(name + 12);
>> +               if (kl < 0 && errno == ENOENT &&
>> +                   strncmp(name + 12, "no", 2) == 0)
>> +                       kl = kldload(name + 14);
>> +       } else {
>>                 errno = ENOENT;
>>                 return (-1);
>>         }
>>
>
> I'm curious about this part of the change.  Why is it necessary to load
> the module in the "allow.mount.noXXXfs" case, when the jail is forbidden to
> mount the filesystem? It seems like that would just load modules that
> aren't going to be used.
>
> Additional discussion at https://github.com/iocage/iocage/issues/689 .
>
> -Alan
>
>
> Presumably such a parameter would be included in some jails in conjunction
> with the positive being included in others (perhaps as a default).  The
> truth is I never really considered whether the "no" option would be used, I
> just always treat these option as pairs.
>
> It may be reasonable (at least in the allow.mount.* case) to silently
> disregard a "no" option that doesn't exist, but I don't know how many
> places would need to be modified for that to go smoothly.  Though I don't
> expect that there would be too many people who bother to include a jail
> parameter about a filesystem which they're not planning to use.
>
> - Jamie
>

Well, many people use the "no" option because one of the most popular jail
managers, iocage, uses it under the hood.  But since "no" is the default,
its presence on the command line is a noop.  Are there any situations in
which the "no" option has an effect?  The only two possibilities I could
think of were:

1) Somebody puts both the positive and negative options on the same command
line.  From experiment, it seems like the last option takes effect.  In
this case, the presence of the positive option would cause the kld to be
loaded, regardless of the presence of the negative option.
2) When using hierarchical jails, it might make sense to use the positive
option for the outer jail and the negative option for the inner jail.  But
this would only be important if the inner jail inherited the outer jail's
parameters, which doesn't seem to be the case.

So I can't think of any reason to continue to mount the kld for "no"
options.  Can you?