netdev - Re: [PATCH net] net: fix skb leak in __skb_tstamp

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Date: Mon, 22 May 2023 16:55:05 +0000
From: SeongJae Park <sj@...nel.org>
To: Pratyush Yadav <ptyadav@...zon.de>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Norbert Manthey <nmanthey@...zon.de>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: fix skb leak in __skb_tstamp_tx()

Hi Pratyush,

On Mon, 22 May 2023 17:30:20 +0200 Pratyush Yadav <ptyadav@...zon.de> wrote:

> Commit 50749f2dd685 ("tcp/udp: Fix memleaks of sk and zerocopy skbs with
> TX timestamp.") added a call to skb_orphan_frags_rx() to fix leaks with
> zerocopy skbs. But it ended up adding a leak of its own. When
> skb_orphan_frags_rx() fails, the function just returns, leaking the skb
> it just cloned. Free it before returning.
> 
> This bug was discovered and resolved using Coverity Static Analysis
> Security Testing (SAST) by Synopsys, Inc.
> 
> Fixes: 50749f2dd685 ("tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.")

Seems the commit has merged in several stable kernels.  Is the bug also
affecting those?  If so, would it be better to Cc stable@...r.kernel.org?


Thanks,
SJ

> Signed-off-by: Pratyush Yadav <ptyadav@...zon.de>
> ---
> 
> I do not know this code very well, this was caught by our static
> analysis tool. I did not try specifically reproducing the leak but I did
> do a boot test by adding this patch on 6.4-rc3 and the kernel boots
> fine.
> 
>  net/core/skbuff.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 515ec5cdc79c..cea28d30abb5 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5224,8 +5224,10 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
>  	} else {
>  		skb = skb_clone(orig_skb, GFP_ATOMIC);
> 
> -		if (skb_orphan_frags_rx(skb, GFP_ATOMIC))
> +		if (skb_orphan_frags_rx(skb, GFP_ATOMIC)) {
> +			kfree_skb(skb);
>  			return;
> +		}
>  	}
>  	if (!skb)
>  		return;
> --
> 2.39.2
>