netdev - Re: [PATCH net] net: sched: fix call_rcu() race on classifier module unloads

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] [day] [month] [year] [list]

Message-Id: <20150521.184857.1038956366531935453.davem@davemloft.net>
Date:	Thu, 21 May 2015 18:48:57 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	subramanian.vijay@...il.com, netdev@...r.kernel.org,
	john.r.fastabend@...el.com, edumazet@...gle.com, tgraf@...g.ch,
	jhs@...atatu.com, ast@...mgrid.com
Subject: Re: [PATCH net] net: sched: fix call_rcu() race on classifier
 module unloads

From: Daniel Borkmann <daniel@...earbox.net>
Date: Wed, 20 May 2015 17:13:33 +0200

> Vijay reported that a loop as simple as ...
 ...
> ... will panic the kernel. Moreover, he bisected the change
> apparently introducing it to 78fd1d0ab072 ("netlink: Re-add
> locking to netlink_lookup() and seq walker").
> 
> The removal of synchronize_net() from the netlink socket
> triggering the qdisc to be removed, seems to have uncovered
> an RCU resp. module reference count race from the tc API.
> Given that RCU conversion was done after e341694e3eb5 ("netlink:
> Convert netlink_lookup() to use RCU protected hash table")
> which added the synchronize_net() originally, occasion of
> hitting the bug was less likely (not impossible though):
> 
> When qdiscs that i) support attaching classifiers and,
> ii) have at least one of them attached, get deleted, they
> invoke tcf_destroy_chain(), and thus call into ->destroy()
> handler from a classifier module.
> 
> After RCU conversion, all classifier that have an internal
> prio list, unlink them and initiate freeing via call_rcu()
> deferral.
> 
> Meanhile, tcf_destroy() releases already reference to the
> tp->ops->owner module before the queued RCU callback handler
> has been invoked.
> 
> Subsequent rmmod on the classifier module is then not prevented
> since all module references are already dropped.
> 
> By the time, the kernel invokes the RCU callback handler from
> the module, that function address is then invalid.
> 
> One way to fix it would be to add an rcu_barrier() to
> unregister_tcf_proto_ops() to wait for all pending call_rcu()s
> to complete.
> 
> synchronize_rcu() is not appropriate as under heavy RCU
> callback load, registered call_rcu()s could be deferred
> longer than a grace period. In case we don't have any pending
> call_rcu()s, the barrier is allowed to return immediately.
> 
> Since we came here via unregister_tcf_proto_ops(), there
> are no users of a given classifier anymore. Further nested
> call_rcu()s pointing into the module space are not being
> done anywhere.
> 
> Only cls_bpf_delete_prog() may schedule a work item, to
> unlock pages eventually, but that is not in the range/context
> of cls_bpf anymore.
> 
> Fixes: 25d8c0d55f24 ("net: rcu-ify tcf_proto")
> Fixes: 9888faefe132 ("net: sched: cls_basic use RCU")
> Reported-by: Vijay Subramanian <subramanian.vijay@...il.com>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied, thanks a lot Daniel.
--
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