From: Eric Garver <e@erig.me>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Pirko <jiri@resnulli.us>,
"David S. Miller" <davem@davemloft.net>,
Alexander Duyck <aduyck@mirantis.com>,
Tom Herbert <tom@herbertland.com>, Jiri Pirko <jiri@mellanox.com>,
Hadar Hen Zion <hadarh@mellanox.com>,
Gao Feng <fgao@48lvckh6395k16k5.yundunddos.com>,
Amir Vadai <amir@vadai.me>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] flow_dissector: avoid uninitialized variable access
Date: Sat, 22 Oct 2016 11:57:52 -0400 [thread overview]
Message-ID: <20161022155752.GD26044@egarver> (raw)
In-Reply-To: <3516805.IZ705sLgKU@wuerfel>
On Sat, Oct 22, 2016 at 12:16:29AM +0200, Arnd Bergmann wrote:
> On Friday, October 21, 2016 11:05:45 PM CEST Arnd Bergmann wrote:
> >
> > Can you explain why "dissector_uses_key(flow_dissector,
> > FLOW_DISSECTOR_KEY_VLAN) && skb_vlan_tag_present(skb)" implies
> > "eth_type_vlan(proto))"?
> >
> > If I add uninitialized_var() here, I would at least put that in
> > a comment here.
>
> Found it now myself: if skb_vlan_tag_present(skb), then we don't
> access 'vlan', otherwise we know it is initialized because
> eth_type_vlan(proto) has to be true.
>
> > On a related note, I also don't see how
> > "dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_VLAN)"
> > implies that skb is non-NULL. I guess this is related to the
> > first one.
>
> I'm still unsure about this one.
Only skb_flow_dissect_flow_keys_buf() calls this function with skb ==
NULL. It uses flow_keys_buf_dissector_keys which does not specify
FLOW_DISSECTOR_KEY_VLAN, so the if statement is false.
A similar assumption is made for FLOW_DISSECTOR_KEY_ETH_ADDRS higher up.
> I also found something else that is suspicious: 'vlan' points
> to the local _vlan variable, but that has gone out of scope
> by the time we access the pointer, which doesn't seem safe.
I see no harm in moving _vlan to the same scope as vlan.
next prev parent reply other threads:[~2016-10-22 15:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-21 15:55 [PATCH] flow_dissector: avoid uninitialized variable access Arnd Bergmann
2016-10-21 16:31 ` Jiri Pirko
2016-10-21 21:05 ` Arnd Bergmann
2016-10-21 22:16 ` Arnd Bergmann
2016-10-22 15:57 ` Eric Garver [this message]
2016-10-22 18:20 ` Tom Herbert
2016-10-22 20:30 ` [PATCH net-next] flow_dissector: fix vlan tag handling Arnd Bergmann
2016-10-24 8:17 ` Jiri Pirko
2016-10-24 16:00 ` Arnd Bergmann
2016-10-22 1:48 ` [PATCH] flow_dissector: avoid uninitialized variable access Linus Torvalds
2016-10-22 6:55 ` Jiri Pirko
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