linux-kernel - Re: [PATCH] net: dsa: microchip: linearize skb for tail-tagging switches

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Message-ID: <e76f230c-a513-4185-ae3f-72c033aeeb1e@lunn.ch>
Date: Fri, 9 May 2025 14:31:00 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Jakob Unterwurzacher <jakobunt@...il.com>
Cc: Woojung Huh <woojung.huh@...rochip.com>, UNGLinuxDriver@...rochip.com,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, quentin.schulz@...rry.de,
	Jakob Unterwurzacher <jakob.unterwurzacher@...rry.de>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	George McCollister <george.mccollister@...il.com>
Subject: Re: [PATCH] net: dsa: microchip: linearize skb for tail-tagging
 switches

On Fri, May 09, 2025 at 09:18:19AM +0200, Jakob Unterwurzacher wrote:
> The pointer arithmentic for accessing the tail tag does not
> seem to handle nonlinear skbs.
> 
> For nonlinear skbs, it reads uninitialized memory inside the
> skb headroom, essentially randomizing the tag, breaking user
> traffic.

Both tag_rtl8_4.c & tag_trailer.c also linearize, so i would say this
is correct.

What is interesting is that both xrs700x_rcv() and
sja1110_rcv_inband_control_extension() also don't call
skb_linearize().

Vladimir? George?

> Tested on v6.12.19 and today's master (d76bb1ebb5587f66b).

Please read:

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html

This patch should be for net, and you need a Fixes: tag.

    Andrew

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