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Message-ID: <289a62a2-e277-41b3-a78f-4ff7a0a23881@huawei.com>
Date: Wed, 3 Sep 2025 20:22:56 +0800
From: Yue Haibing <yuehaibing@...wei.com>
To: Qingfang Deng <dqfext@...il.com>, Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Paul
Mackerras <paulus@...abs.org>, Matt Domsch <Matt_Domsch@...l.com>, Andrew
Morton <akpm@...l.org>, Brice Goglin <Brice.Goglin@...-lyon.org>,
<linux-ppp@...r.kernel.org>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] ppp: fix memory leak in pad_compress_skb
On 2025/9/3 18:07, Qingfang Deng wrote:
> If alloc_skb() fails in pad_compress_skb(), it returns NULL without
> releasing the old skb. The caller does:
>
> skb = pad_compress_skb(ppp, skb);
> if (!skb)
> goto drop;
>
> drop:
> kfree_skb(skb);
>
> When pad_compress_skb() returns NULL, the reference to the old skb is
> lost and kfree_skb(skb) ends up doing nothing, leading to a memory leak.
>
> Align pad_compress_skb() semantics with realloc(): only free the old
> skb if allocation and compression succeed. At the call site, use the
> new_skb variable so the original skb is not lost when pad_compress_skb()
> fails.
>
> Fixes: b3f9b92a6ec1 ("[PPP]: add PPP MPPE encryption module")
> Signed-off-by: Qingfang Deng <dqfext@...il.com>
> ---
> drivers/net/ppp/ppp_generic.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index 65795d099166..f9f0f16c41d1 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -1744,7 +1744,6 @@ pad_compress_skb(struct ppp *ppp, struct sk_buff *skb)
> */
> if (net_ratelimit())
> netdev_err(ppp->dev, "ppp: compressor dropped pkt\n");
> - kfree_skb(skb);
> consume_skb(new_skb);
> new_skb = NULL;
> }
> @@ -1845,9 +1844,10 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
> "down - pkt dropped.\n");
> goto drop;
> }
> - skb = pad_compress_skb(ppp, skb);
> - if (!skb)
> + new_skb = pad_compress_skb(ppp, skb);
> + if (!new_skb)
> goto drop;
> + skb = new_skb;
> }
>
> /*
Reviewed-by: Yue Haibing <yuehaibing@...wei.com>
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