From: Paul Mackerras <paulus@ozlabs.org>
To: Yilin Zhang <yilinzhang@moonshot.ai>
Cc: linux-ppp@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
Kimi Security Team <bug-report@moonshot.ai>,
Weiming Shi <shiweiming@moonshot.ai>
Subject: Re: [PATCH net] ppp: deflate: validate output buffer sizes
Date: Mon, 7 Sep 2026 16:45:00 +1000 [thread overview]
Message-ID: <ap5dbA8dh0fT6bP-@bruin> (raw)
In-Reply-To: <20260907055809.3379942-1-yilinzhang@moonshot.ai>
On Mon, Sep 07, 2026 at 01:58:09PM +0800, Yilin Zhang wrote:
> z_compress() assumes that the output buffer can hold the six-byte
> PPP/Deflate header. With an MTU of 1, pad_compress_skb() supplies an
> output size of 5. The header write overruns the skb and subtracting the
> header length makes avail_out wrap, allowing zlib to continue writing
> past the allocation.
Why not rather enforce a reasonable minimum for the MTU? I don't see
how an MTU of 1 is practically useful in any way. A practical minimum
would be on the order or 100; when negotiating with the peer, pppd
naks anything less than 128 and proposes 128 instead.
Paul.
prev parent reply other threads:[~2026-09-07 6:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-07 5:58 [PATCH net] ppp: deflate: validate output buffer sizes Yilin Zhang
2026-09-07 6:45 ` Paul Mackerras [this message]
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