cvs commit: src/sys/nfsclient nfs_socket.c

[Robert Watson]

On Thu, 10 Jan 2008, Alfred Perlstein wrote:

>>>>   Pass curthread to various socket routines (socreate(), sobind(), and
>>>>   soconnect()) instead of &thread0 when establishing a connection to the NFS
>>>>   server.  Otherwise inconsistent credentials may be used when setting up
>>>>   the NFS socket.
>>>
>>> I'm not sure, but I think this may be a regression, I seem to recall that 
>>> a long time ago it was switched to &thread0 because otherwise certain 
>>> operations can fail due to curthread not running as root.
>>
>> That's my recollection too.  For example, when nfs is configured to bind to 
>> a priviliged local port for making queries or connections, it had to be 
>> done as root.  With tcp mounts, the connection can be dropped and a 
>> reconnect required at any time.
>
> This could be implemented by a handoff to a thread that does the appropriate 
> setuid call beforehand, or perhaps the credential inconsistencies can be 
> further expained or fixed.

The real bug is that sobind() and soconnect() take threads as arguments, and 
should either take just credentials or credentials and threads depending on 
whether they really want a thread as well.  I started fixing this a few years 
ago but it requires touching a lot of stuff (like protosw) so is pretty 
disruptive.  Basically, because they accept a thread as an argument, you can't 
use the cached mount-time credential to authorize these further socket 
operations.  You don't want to used the cached socket()-time credential, 
another obvious choice, as you want to be able to have the root user 
bind()/connect() a socket and then hand it off to unprivileged processes to 
use without being able to rebind/connect with privilege.

Possibly the above change should be modified to use curthread for UDP and 
thread0 for TCP, as TCP can be reconnected but may not have the bind problem 
John is running into, whereas UDP won't be reconnected?

Robert N M Watson
Computer Laboratory
University of Cambridge