netdev - Re: [PATCH 3/3] tap: free skb if flags error

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Date:   Fri, 1 Dec 2017 16:48:25 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     wexu@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jasowang@...hat.com,
        mjrosato@...ux.vnet.ibm.com
Subject: Re: [PATCH 3/3] tap: free skb if flags error

On Fri, Dec 01, 2017 at 05:10:38AM -0500, wexu@...hat.com wrote:
> From: Wei Xu <wexu@...hat.com>
> 
> tap_recvmsg() supports accepting skb by msg_control after
> commit 3b4ba04acca8 ("tap: support receiving skb from msg_control"),
> the skb if presented should be freed within the function, otherwise
> it would be leaked.
> 
> Signed-off-by: Wei Xu <wexu@...hat.com>
> Reported-by: Matthew Rosato <mjrosato@...ux.vnet.ibm.com>


Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/net/tap.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index e9489b8..0a886fda 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -829,8 +829,11 @@ static ssize_t tap_do_read(struct tap_queue *q,
>  	DEFINE_WAIT(wait);
>  	ssize_t ret = 0;
>  
> -	if (!iov_iter_count(to))
> +	if (!iov_iter_count(to)) {
> +		if (skb)
> +			kfree_skb(skb);
>  		return 0;
> +	}
>  
>  	if (skb)
>  		goto put;
> @@ -1154,11 +1157,14 @@ static int tap_recvmsg(struct socket *sock, struct msghdr *m,
>  		       size_t total_len, int flags)
>  {
>  	struct tap_queue *q = container_of(sock, struct tap_queue, sock);
> +	struct sk_buff *skb = m->msg_control;
>  	int ret;
> -	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
> +	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC)) {
> +		if (skb)
> +			kfree_skb(skb);
>  		return -EINVAL;
> -	ret = tap_do_read(q, &m->msg_iter, flags & MSG_DONTWAIT,
> -			  m->msg_control);
> +	}
> +	ret = tap_do_read(q, &m->msg_iter, flags & MSG_DONTWAIT, skb);
>  	if (ret > total_len) {
>  		m->msg_flags |= MSG_TRUNC;
>  		ret = flags & MSG_TRUNC ? ret : total_len;
> -- 
> 1.8.3.1