netdev - Re: [Patch net] af_key: relax availability checks for skb size calculation

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Message-ID: <20210105080924.GH3576117@gauss3.secunet.de>
Date:   Tue, 5 Jan 2021 09:09:24 +0100
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     <netdev@...r.kernel.org>, Cong Wang <cong.wang@...edance.com>,
        <syzbot+b2bf2652983d23734c5c@...kaller.appspotmail.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [Patch net] af_key: relax availability checks for skb size
 calculation

On Sat, Dec 26, 2020 at 04:50:20PM -0800, Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
> 
> xfrm_probe_algs() probes kernel crypto modules and changes the
> availability of struct xfrm_algo_desc. But there is a small window
> where ealg->available and aalg->available get changed between
> count_ah_combs()/count_esp_combs() and dump_ah_combs()/dump_esp_combs(),
> in this case we may allocate a smaller skb but later put a larger
> amount of data and trigger the panic in skb_put().
> 
> Fix this by relaxing the checks when counting the size, that is,
> skipping the test of ->available. We may waste some memory for a few
> of sizeof(struct sadb_comb), but it is still much better than a panic.
> 
> Reported-by: syzbot+b2bf2652983d23734c5c@...kaller.appspotmail.com
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>

Patch applied, thanks!