netdev - Re: [PATCH net v2] ppp: reject claimed-as-LCP but actually malformed packets

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Message-ID: <20240709083012.GD346094@kernel.org>
Date: Tue, 9 Jul 2024 09:30:12 +0100
From: Simon Horman <horms@...nel.org>
To: Dmitry Antipov <dmantipov@...dex.ru>
Cc: "David S. Miller" <davem@...emloft.net>,
	"Ricardo B. Marliere" <ricardo@...liere.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	linux-ppp@...r.kernel.org, netdev@...r.kernel.org,
	lvc-project@...uxtesting.org,
	syzbot+ec0723ba9605678b14bf@...kaller.appspotmail.com,
	Guillaume Nault <gnault@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net v2] ppp: reject claimed-as-LCP but actually malformed
 packets

+ Guillaume, Jakub

On Mon, Jul 08, 2024 at 02:56:15PM +0300, Dmitry Antipov wrote:
> Since 'ppp_async_encode()' assumes valid LCP packets (with code
> from 1 to 7 inclusive), add 'ppp_check_packet()' to ensure that
> LCP packet has an actual body beyond PPP_LCP header bytes, and
> reject claimed-as-LCP but actually malformed data otherwise.
> 
> Reported-by: syzbot+ec0723ba9605678b14bf@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ec0723ba9605678b14bf
> Fixes: 44073187990d ("ppp: ensure minimum packet size in ppp_write()")

Sorry for not noticing this earlier.

I think that the cited commit is not where this problem was introduced.
What that commit does is to introduce a length check.
And what this patch does is to add another, more specific length check.
But the problem fixed by this patch existed before the cited commit.

I expect that, like the cited commit, this patch:

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

> Signed-off-by: Dmitry Antipov <dmantipov@...dex.ru>
> ---
> v2: style, comments, and metadata adjustments suggested by Simon Horman

Thanks, other than the Fixes tag, this looks good to me.

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

...