Re: [PATCH net] net: fix skb leak in __skb_tstamp_tx()

From: Kuniyuki Iwashima <kuniyu@amazon.com>
To: <ptyadav@amazon.de>
Cc: <davem@davemloft.net>, <edumazet@google.com>, <kuba@kernel.org>,
	<kuniyu@amazon.com>, <linux-kernel@vger.kernel.org>,
	<netdev@vger.kernel.org>, <nmanthey@amazon.de>,
	<pabeni@redhat.com>, <willemb@google.com>
Subject: Re: [PATCH net] net: fix skb leak in __skb_tstamp_tx()
Date: Mon, 22 May 2023 08:45:54 -0700	[thread overview]
Message-ID: <20230522154554.44836-1-kuniyu@amazon.com> (raw)
In-Reply-To: <20230522153020.32422-1-ptyadav@amazon.de>

From: Pratyush Yadav <ptyadav@amazon.de>
Date: Mon, 22 May 2023 17:30:20 +0200
> 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.")
> Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Good catch, thanks!

> ---
> 
> 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