netdev - Re: [PATCH] fix race in AF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <m1ir9eaahu.fsf@ebiederm.dsl.xmission.com>
Date:	Sat, 23 Jun 2007 10:42:05 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	davem@...emloft.net, viro@....linux.org.uk,
	alan@...rguk.ukuu.org.uk, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix race in AF_UNIX

Miklos Szeredi <miklos@...redi.hu> writes:

> Right.  But the devil is in the details, and (as you correctly point
> out later) to implement this, the whole locking scheme needs to be
> overhauled.  Problems:
>
>  - Using the queue lock to make the dequeue and the fd detach atomic
>    wrt the GC is difficult, if not impossible: they are are far from
>    each other with various magic in between.  It would need thorough
>    understanding of these functions and _big_ changes to implement.
>
>  - Sleeping on u->readlock in GC is currently not possible, since that
>    could deadlock with unix_dgram_recvmsg().  That function could
>    probably be modified to release u->readlock, while waiting for
>    data, similarly to unix_stream_recvmsg() at the cost of some added
>    complexity.
>
>  - Sleeping on u->readlock is also impossible, because GC is holding
>    unix_table_lock for the whole operation.  We could release
>    unix_table_lock, but then would have to cope with sockets coming
>    and going, making the current socket iterator unworkable.
>
> So theoretically it's quite simple, but it needs big changes.  And
> this wouldn't even solve all the problems with the GC, like being a
> possible DoS vector.

Making the GC fully incremental will solve the DoS vector problem as
well.  Basically you do a fixed amount of reclaim in the new socket
allocation code.

It appears clear that since we can't stop the world and garbage
collect we need an incremental collector.

Eric
-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html