netdev - Re: [PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet

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Message-Id: <20181119.123955.865697238943438515.davem@davemloft.net>
Date:   Mon, 19 Nov 2018 12:39:55 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        marcelo.leitner@...il.com, nhorman@...driver.com
Subject: Re: [PATCH net] sctp: count sk_wmem_alloc by skb truesize in
 sctp_packet_transmit

From: Xin Long <lucien.xin@...il.com>
Date: Sun, 18 Nov 2018 15:07:38 +0800

> Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
> skb allocked in sctp_packet_transmit and decreases by 1 when freeing
> this skb.
> 
> But when this skb goes through networking stack, some subcomponents
> might change skb->truesize and add the same amount on sk_wmem_alloc.
> However sctp doesn't know the amount to decrease by, it would cause
> a leak on sk->sk_wmem_alloc and the sock can never be freed.
> 
> Xiumei found this issue when it hit esp_output_head() by using sctp
> over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.
> 
> Since sctp has used sk_wmem_queued to count for writable space since
> Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
> space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
> in sctp_packet_transmit.
> 
> Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Applied and queued up for -stable.