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Date:	Wed, 21 May 2014 10:41:57 -0700
From:	Eric Dumazet <>
To:	Alexander Duyck <>
Cc:	Alexander Duyck <>,
	David Miller <>,,,,,,,,,,,,,
Subject: Re: [PATCH net-next 1/2] net: Expose header length compution

On Wed, 2014-05-21 at 09:45 -0700, Alexander Duyck wrote:

> We have had stack smashing issues in the past with the ixgbe interrupt
> handlers and it wasn't consuming much memory on the stack as I recall. 
> I prefer to err on the side of caution.

Well, if we can not temporarily use 256 bytes in a leaf function in rx
handler of a driver, how IP + TCP stack will ever work ?

> Also the more I think about it I am not really comfortable putting a
> partially initialized sk_buff through any function calls.  It seems like
> it is setting somebody up for a failure because if at some point the
> code changes and needs some other field out of the skb it won't be
> initialized here unless they catch this tricky bit of code.

We are speaking of flow_dissect, which is a leaf function if 
data_len = 0

The fields I setup are the only ones that can be read from flow

We look at a frame, given a starting point (network header) and protocol

Apparent complexity is apparent only : skb_header_pointer() is basically
a nop if data_len = 0

Sure, you can add a

   memset(&skb, 0x6b, sizeof(skb));

And I did/tried that before sending the patch ;)

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