Re: [redhat-lspp] Re: [PATCH 2/3] Re: MLS enforcing PTYs, sshd, and newrole

[Joshua Brindle <jbrindle@tresys.com>]

Klaus Weidner wrote:
> On Thu, Jan 04, 2007 at 06:19:13PM -0500, Linda Knippers wrote:
>   
>>> devices.txt in kernel documentation. 
>>> 2176 <http://www.mjmwired.net/kernel/Documentation/devices.txt#2176>    136-143 char    Unix98 PTY slaves 
>>>       
>> Since that document has multiple devices with the same major, I wonder if its
>> safer to fstatfs() the fd and make sure the f_type is the devpts fs magic
>> number.  It only seems to be defined in fs/devpts/inode.c though.
>>
>>     
>>> #define DEVPTS_SUPER_MAGIC 0x1cd1
>>>       
>> devpts is mounted on /dev/pts before single user mode so it seems to always
>> be there unless someone unmounts it.  If you try to ssh in without /dev/pts
>> mounted the ssh hangs.
>>     
>
> I think blacklists are usually a bad idea for security, for example this
> breaks if people have a kernel that supports the old-style ptys that
> don't use devpts. How about turning it around and only allowing use of
> known good ttys, similar to /etc/securetty, or insisting on type
> "tty_device_t" which includes the virtual console and serial terminals
> but not the ptys?
>   
Hardcoding types into code makes it inflexible to policy changes, this 
is a bad idea IMO, the tty whitelist, however, is probably the way to 
go. I don't know if we should use the existing /etc/securetty or  add 
our own file though.


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