netdev - Re: [PATCH net-next,v3 02/12] gtp: properly parse extension headers

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Date: Thu, 9 May 2024 13:14:41 +0100
From: Simon Horman <horms@...nel.org>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
	pabeni@...hat.com, edumazet@...gle.com, laforge@...ocom.org,
	pespin@...mocom.de, osmith@...mocom.de
Subject: Re: [PATCH net-next,v3 02/12] gtp: properly parse extension headers

On Tue, May 07, 2024 at 01:52:41AM +0200, Pablo Neira Ayuso wrote:
> Currently GTP packets are dropped if the next extension field is set to
> non-zero value, but this are valid GTP packets.
> 
> TS 29.281 provides a longer header format, which is defined as struct
> gtp1_header_long. Such long header format is used if any of the S, PN, E
> flags is set.
> 
> This long header is 4 bytes longer than struct gtp1_header, plus
> variable length (optional) extension headers. The next extension header
> field is zero is no extension header is provided.
> 
> The extension header is composed of a length field which includes total
> number of 4 byte words including the extension header itself (1 byte),
> payload (variable length) and next type (1 byte). The extension header
> size and its payload is aligned to 4 bytes.
> 
> A GTP packet might come with a chain extensions headers, which makes it
> slightly cumbersome to parse because the extension next header field
> comes at the end of the extension header, and there is a need to check
> if this field becomes zero to stop the extension header parser.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>

Reviewed-by: Simon Horman <horms@...nel.org>