linux-kernel - Re: [PATCH RFC net] ps3/gelic: Fix possible NULL pointer dereference

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Message-ID: <CAMuHMdXSmf6cKxzzXBYC5Zrkj6QR+2EhB4346d3g-RNTS+W7AQ@mail.gmail.com>
Date: Thu, 22 Feb 2024 09:45:31 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Simon Horman <horms@...nel.org>
Cc: Geoff Levand <geoff@...radead.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>, 
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, Jeff Garzik <jeff@...zik.org>, 
	Dan Carpenter <dan.carpenter@...aro.org>, netdev@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net] ps3/gelic: Fix possible NULL pointer dereference

Hi Simon,

On Wed, Feb 21, 2024 at 5:57 PM Simon Horman <horms@...nel.org> wrote:
> Fix possible NULL pointer dereference in gelic_card_release_tx_chain()
>
> The cited commit introduced a netdev variable to
> gelic_card_release_tx_chain() which is set unconditionally on each
> iteration of a for loop.
>
> It is set to the value of tx_chain->tail->skb->dev.  However, in some
> cases it is assumed that tx_chain->tail->skb may be NULL. And if that
> occurs, setting netdev will cause a NULl pointer dereference.

Thanks for your patch!

> Given the age of this code I do wonder if this can occur in practice.
> But to be on the safe side this patch assumes that it can and aims to
> avoid the dereference in the case where tx_chain->tail->skb may be NULL.

The compiler may also lazy-load netdev until it's actually used,
avoiding the crash?

> Fixes: 589866f9f1cb ("PS3: gelic: Add support for dual network interface")
> Signed-off-by: Simon Horman <horms@...nel.org>

Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds