kernel panic on jailed sshd - 4.9-release

[Oliver Fromme]

Marc G. Fournier <scrappy at hub.org> wrote:
 > On Tue, 11 Nov 2003, Oliver Fromme wrote:
 > > Kovács János <kovacs.janos at ofi.hu> wrote:
 > >  > Just installed 4.9-RELEASE with jailed sshd over a null-mounted (bin,
 > >  > dev,etc,usr)
 > >  > dirs crashing.
 > >
 > > It's well-known that NULLFS (as well as UNIONFS) are unstable
 > > in FreeBSD 4.x and can cause crashes.
 > 
 > God, I so hate answers like this ... its the "I'm too lazy to care"
 > answer ...

If I had been lazy, I wouldn't have written an answer at
all.

In most cases when machines crash and NULLFS is in use,
the latter is causing it.

 > ... and it doesn't even come close to addressing the problem, and that is
 > that in 4.8, he didn't have this problem, while in 4.9, he does ...

Possibly a program which now triggers a NULLFS problem.
For example, it might be that some program in 4.8 used
standard read/write to access files, and it was changed
to use mmap() in 4.9, which can be a problem with NULLFS.

Of course I could be wrong.  Something else could have
caused that particular crash.  But still it is a good
idea not to use NULLFS if possible.  (Particularly in a
jail environment if you don't have strict control over
which programs get executed, such as a user shell box.)

If a miracle happened and NULLFS got stable recently,
then the mount_null(8) manpage should be fixed, because
it states just the opposite.  ;-)

Regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.

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