netdev - Re: [PATCH] net/x25: Fix x25_neigh refcnt leak when reveiving frame

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Date:   Thu, 23 Apr 2020 15:14:18 +0800
From:   Yuehaibing <yuehaibing@...wei.com>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Andrew Hendry <andrew.hendry@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Allison Randal <allison@...utok.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        <linux-x25@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <yuanxzhang@...an.edu.cn>, <kjlu@....edu>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] net/x25: Fix x25_neigh refcnt leak when reveiving frame

On 2020/4/23 13:13, Xiyu Yang wrote:
> x25_lapb_receive_frame() invokes x25_get_neigh(), which returns a
> reference of the specified x25_neigh object to "nb" with increased
> refcnt.
> 
> When x25_lapb_receive_frame() returns, local variable "nb" becomes
> invalid, so the refcount should be decreased to keep refcount balanced.
> 
> The reference counting issue happens in one path of
> x25_lapb_receive_frame(). When pskb_may_pull() returns false, the
> function forgets to decrease the refcnt increased by x25_get_neigh(),
> causing a refcnt leak.
> 
> Fix this issue by calling x25_neigh_put() when pskb_may_pull() returns
> false.
> 

Fixes: cb101ed2c3c7 ("x25: Handle undersized/fragmented skbs")

> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> ---
>  net/x25/x25_dev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/x25/x25_dev.c b/net/x25/x25_dev.c
> index 00e782335cb0..25bf72ee6cad 100644
> --- a/net/x25/x25_dev.c
> +++ b/net/x25/x25_dev.c
> @@ -115,8 +115,10 @@ int x25_lapb_receive_frame(struct sk_buff *skb, struct net_device *dev,
>  		goto drop;
>  	}
>  
> -	if (!pskb_may_pull(skb, 1))
> +	if (!pskb_may_pull(skb, 1)) {
> +		x25_neigh_put(nb);
>  		return 0;
> +	}
>  
>  	switch (skb->data[0]) {
>  
>