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Message-ID: <49227D7C.5050601@op5.se>
Date: Tue, 18 Nov 2008 09:31:56 +0100
From: Andreas Ericsson <ae@....se>
To: oss-security@...ts.openwall.com
Subject: Re: CVE Request (syslog-ng)
Solar Designer wrote:
> On Mon, Nov 17, 2008 at 11:06:53PM +0100, Andreas Ericsson wrote:
>> The correct sequence is:
>> chdir(jail_path);
>> chroot(".");
>
> That's a correct sequence, but not the only correct one.
>
Well, "chroot(jail_path); chdir("/");" does effectively the same
thing (ie, avoid re-using jail_path), so they're equally race-
resistant, ofcourse.
>> The chroot() call will fail if the directory no longer exists,
>
> No. I'm not sure if this is required by any standard, by the behavior
> I'm used to seeing is that the current directory for a process will sort
> of continue to exist for that process despite of being removed.
This doesn't hold true on VMS and some Irix releases. Now that you
say it, I haven't run into it on more recent systems, but I remember
it happening on those about two years back at a customers site.
HP dev-center used to have an (Open)VMS system, but I can't seem to
find it now, or I would verify it there.
>> Paranoid programs only accept absolute non-symlink paths to the jail
>> and issue getcwd() after having entered it to make sure they ended up
>> in the proper directory.
>
> I find this ridiculous - a program can't possibly defend itself against
> every kind of unsafe use by the sysadmin. If a program chooses to do
> any sanity checking on the provided pathname, then a sane check would be
> to ensure that all directories in the path are only writable by root.
That would fail with Owl's setup of per-user /tmp/.private/$USER dirs,
even if those are absolutely safe for chroot-jail usage otherwise.
Assuming no symlinks, it's enough to ensure that "." and ".." are root-
owned and 0700 once the directory has been entered, and quite a lot
simpler. This has been verified by at least eight separate security
researchers in severely paranoid industries (weapons research among
others).
>
> Besides the missing chdir(), another very common issue with "privilege
> dropping" programs is forgetting to drop or re-initialize supplementary
> groups. Not checking return values from any of the functions involved
> is about as common... (I have not checked syslog-ng for any of this.)
>
It's not stellar in that respect. Here's the effective code, printable
with "sed -n 275,297p src/main.c" from the latest syslog-ng snapshot.
--8<--8<--8<--
int
setup_creds(void)
{
if (chroot_dir)
{
if (chroot(chroot_dir) < 0)
{
msg_error("Error during chroot()",
evt_tag_errno(EVT_TAG_OSERROR, errno),
NULL);
return 0;
}
}
if (uid || gid || run_as_user)
{
setgid(gid);
if (run_as_user)
initgroups(run_as_user, gid);
setuid(uid);
}
return 1;
}
--8<--8<--8<--
--
Andreas Ericsson andreas.ericsson@....se
OP5 AB www.op5.se
Tel: +46 8-230225 Fax: +46 8-230231
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