Re: [PATCH net] ppp: fix memory leak in pad_compress_skb

[Yue Haibing <yuehaibing@huawei.com>]

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@gmail.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@huawei.com>