linux-kernel - Re: [PATCH net-next v4 1/1] ppp: Fix KMSAN warning by initializing 2-byte header

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Message-ID: <20250227174812.50d2eabe@kernel.org>
Date: Thu, 27 Feb 2025 17:48:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: horms@...nel.org, bpf@...r.kernel.org, netdev@...r.kernel.org,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, ricardo@...liere.net, viro@...iv.linux.org.uk,
 dmantipov@...dex.ru, aleksander.lobakin@...el.com,
 linux-ppp@...r.kernel.org, linux-kernel@...r.kernel.org, mrpre@....com,
 syzbot+853242d9c9917165d791@...kaller.appspotmail.com
Subject: Re: [PATCH net-next v4 1/1] ppp: Fix KMSAN warning by initializing
 2-byte header

On Wed, 26 Feb 2025 09:36:58 +0800 Jiayuan Chen wrote:
> The PPP driver adds an extra 2-byte header to enable socket filters to run
> correctly. However, the driver only initializes the first byte, which
> indicates the direction. For normal BPF programs, this is not a problem
> since they only read the first byte.
> 
> Nevertheless, for carefully crafted BPF programs, if they read the second
> byte, this will trigger a KMSAN warning for reading uninitialized data.
> 
> Reported-by: syzbot+853242d9c9917165d791@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/bpf/000000000000dea025060d6bc3bc@google.com/
> Signed-off-by: Jiayuan Chen <jiayuan.chen@...ux.dev>

Could you add:

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

And combine the cover letter with the commit message?
For a single-patch postings cover letter is not necessary.

> +		*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_OUTBOUND_TAG);
>  		if (ppp->pass_filter &&
>  		    bpf_prog_run(ppp->pass_filter, skb) == 0) {
>  			if (ppp->debug & 1)

The exact same problem seems to be present in ppp_receive_nonmp_frame()
please fix them both.
-- 
pw-bot: cr