netdev - Re: [PATCH] net/decnet: fix -EFAULT error that is not getting returned

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Date:   Wed, 4 Dec 2019 09:39:24 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Colin King <colin.king@...onical.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-decnet-user@...ts.sourceforge.net, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/decnet: fix -EFAULT error that is not getting
 returned



On 12/4/19 7:11 AM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently an -EFAULT error on a memcpy_to_msg is not being returned
> because it is being overwritten when variable rv is being re-assigned
> to the number of bytes copied after breaking out of a loop. Fix this
> by instead assigning the error to variable copied so that this error
> code propegated to rv and hence is returned at the end of the function.
> 
> [ This bug was was introduced before the current git history ]
> 
> Addresses-Coverity: ("Unused value")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  net/decnet/af_decnet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
> index e19a92a62e14..e23d9f219597 100644
> --- a/net/decnet/af_decnet.c
> +++ b/net/decnet/af_decnet.c
> @@ -1759,7 +1759,7 @@ static int dn_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
>  			chunk = size - copied;
>  
>  		if (memcpy_to_msg(msg, skb->data, chunk)) {
> -			rv = -EFAULT;
> +			copied = -EFAULT;

This does not look right.

We probably want :
		if (!copied)
			copied = -EFAULT;

>  			break;
>  		}
>  		copied += chunk;
>