linux-kernel - Re: [PATCH v2] net: don't unconditionally copy_from

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Message-ID: <20210831093006.6db30672@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 31 Aug 2021 09:30:06 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Peter Collingbourne <pcc@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Colin Ian King <colin.king@...onical.com>,
        Cong Wang <cong.wang@...edance.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg KH <gregkh@...uxfoundation.org>,
        David Laight <David.Laight@...lab.com>,
        Arnd Bergmann <arnd@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] net: don't unconditionally copy_from_user a struct
 ifreq for socket ioctls

On Thu, 26 Aug 2021 12:46:01 -0700 Peter Collingbourne wrote:
> @@ -3306,6 +3308,8 @@ static int compat_ifr_data_ioctl(struct net *net, unsigned int cmd,
>  	struct ifreq ifreq;
>  	u32 data32;
>  
> +	if (!is_socket_ioctl_cmd(cmd))
> +		return -ENOTTY;
>  	if (copy_from_user(ifreq.ifr_name, u_ifreq32->ifr_name, IFNAMSIZ))
>  		return -EFAULT;
>  	if (get_user(data32, &u_ifreq32->ifr_data))

Hi Peter, when resolving the net -> net-next merge conflict I couldn't
figure out why this chunk is needed. It seems all callers of
compat_ifr_data_ioctl() already made sure it's a socket IOCTL.
Please double check my resolution (tip of net-next) and if this is
indeed unnecessary perhaps send a cleanup? Thanks!