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From: Arnd Bergmann <>
To: Jiri Pirko <>
Cc: "David S. Miller" <>,
	Alexander Duyck <>,
	Tom Herbert <>, Jiri Pirko <>,
	Hadar Hen Zion <>,
	Gao Feng <>,
	Eric Garver <>, Amir Vadai <>,,
Subject: Re: [PATCH] flow_dissector: avoid uninitialized variable access
Date: Fri, 21 Oct 2016 23:05:45 +0200	[thread overview]
Message-ID: <5467015.N4DG5uA0DU@wuerfel> (raw)
In-Reply-To: <20161021163118.GA2155@nanopsycho.orion>

On Friday, October 21, 2016 6:31:18 PM CEST Jiri Pirko wrote:
> Fri, Oct 21, 2016 at 05:55:53PM CEST, wrote:
> >gcc warns about an uninitialized pointer dereference in the vlan
> >priority handling:
> >
> >net/core/flow_dissector.c: In function '__skb_flow_dissect':
> >net/core/flow_dissector.c:281:61: error: 'vlan' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >
> >From all I can tell, this warning is about a real bug, and we
> >should not attempt look up the vlan header if there was
> >no vlan tag.
> I don't see how vlan could be used uninitialized. But I understand that
> this is impossible for gcc to track it. Please just use uninitialized_var()

I usually try to avoid uninitialized_var(), as making it obvious to
the compiler why something is known tends to result in more readable
source code and better object code.

Can you explain why "dissector_uses_key(flow_dissector,
FLOW_DISSECTOR_KEY_VLAN) && skb_vlan_tag_present(skb)" implies

If I add uninitialized_var() here, I would at least put that in
a comment here.

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.


  reply	other threads:[~2016-10-21 21:06 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 [this message]
2016-10-21 22:16     ` Arnd Bergmann
2016-10-22 15:57       ` Eric Garver
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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