netdev - Re: [PATCH] net: fix for a race condition in the inet frag code

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]

Date:	Mon, 03 Mar 2014 16:34:51 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	nikolay@...hat.com
Cc:	netdev@...r.kernel.org, brouer@...hat.com
Subject: Re: [PATCH] net: fix for a race condition in the inet frag code

From: Nikolay Aleksandrov <nikolay@...hat.com>
Date: Mon,  3 Mar 2014 15:05:20 +0100

> I stumbled upon this very serious bug while hunting for another one,
> it's a very subtle race condition between inet_frag_evictor,
> inet_frag_intern and the IPv4/6 frag_queue and expire functions (basically
> the users of inet_frag_kill/inet_frag_put).
> What happens is that after a fragment has been added to the hash chain but
> before it's been added to the lru_list (inet_frag_lru_add), it may get
> deleted (either by an expired timer if the system load is high or the
> timer sufficiently low, or by the fraq_queue function for different
> reasons) before it's added to the lru_list, then after it gets added
> it's a matter of time for the evictor to get to a piece of memory which
> has been freed leading to a number of different bugs depending on what's
> left there. I've been able to trigger this on both IPv4 and IPv6 (which
> is normal as the frag code is the same), but it's been much more
> difficult to trigger on IPv4 due to the protocol differences about how
> fragments are treated. The setup I used to reproduce this is:
> 2 machines with 4 x 10G bonded in a RR bond, so the same flow can be
> seen on multiple cards at the same time. Then I used multiple instances
> of ping/ping6 to generate fragmented packets and flood the machines with
> them while running other processes to load the attacked machine.
> *It is very important to have the _same flow_ coming in on multiple CPUs
> concurrently. Usually the attacked machine would die in less than 30
> minutes, if configured properly to have many evictor calls and timeouts
> it could happen in 10 minutes or so.
> 
> The fix is simple, just move the lru_add under the hash chain locked
> region so when a removing function is called it'll have to wait for the
> fragment to be added to the lru_list, and then it'll remove it (it works
> because the hash chain removal is done before the lru_list one and
> there's no window between the two list adds when the frag can get
> dropped). With this fix applied I couldn't kill the same machine in 24
> hours with the same setup.
> 
> Fixes: 3ef0eb0db4bf ("net: frag, move LRU list maintenance outside of
> rwlock")
> 
> CC: Jesper Dangaard Brouer <brouer@...hat.com>
> CC: David S. Miller <davem@...emloft.net>
> 
> Signed-off-by: Nikolay Aleksandrov <nikolay@...hat.com>

Nik, please beef up the commit message a bit and resubmit.

Some of your replies explained the situation a bit better.  Don't
be afraid of making the commit message too long or too verbose :-)

Thanks!
--
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