linux-kernel - Re: [PATCH 2/3] tun: free skb in early errors

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Date:   Fri, 1 Dec 2017 15:07:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     wexu@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     mst@...hat.com, mjrosato@...ux.vnet.ibm.com
Subject: Re: [PATCH 2/3] tun: free skb in early errors



On 2017年12月01日 13:54, wexu@...hat.com wrote:
> From: Wei Xu <wexu@...hat.com>
>
> tun_recvmsg() supports accepting skb by msg_control after
> commit ac77cfd4258f ("tun: support receiving skb through 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>
> ---
>   drivers/net/tun.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 6a7bde9..5563430 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2067,14 +2067,17 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
>   {
>   	struct tun_file *tfile = container_of(sock, struct tun_file, socket);
>   	struct tun_struct *tun = tun_get(tfile);
> +	struct sk_buff *skb = m->msg_control;
>   	int ret;
>   
> -	if (!tun)
> -		return -EBADFD;
> +	if (!tun) {
> +		ret = -EBADFD;
> +		goto out_free_skb;

Unfortunately, you can't to there since tun is NULL.


> +	}
>   
>   	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
>   		ret = -EINVAL;
> -		goto out;
> +		goto out_free_skb;
>   	}
>   	if (flags & MSG_ERRQUEUE) {
>   		ret = sock_recv_errqueue(sock->sk, m, total_len,
> @@ -2087,6 +2090,11 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
>   		m->msg_flags |= MSG_TRUNC;
>   		ret = flags & MSG_TRUNC ? ret : total_len;
>   	}
> +	goto out;

We usually don't use goto in the case of success, and you need deal with 
the case skb != NULL but iov_iter_count(to) == 0 in tun_do_read().

Thanks

> +
> +out_free_skb:
> +	if (skb)
> +		kfree_skb(skb);
>   out:
>   	tun_put(tun);
>   	return ret;