netdev - RE: [PATCH v2] net: don't unconditionally copy_from

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Message-ID: <bf0f47974d7141358d810d512d4b9a00@AcuMS.aculab.com>
Date:   Wed, 1 Sep 2021 08:22:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jakub Kicinski' <kuba@...nel.org>,
        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>,
        "Arnd Bergmann" <arnd@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2] net: don't unconditionally copy_from_user a struct
 ifreq for socket ioctls

From: Jakub Kicinski
> Sent: 31 August 2021 17:30
> 
> 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!

To stop the copy_from_user() faulting when the user buffer
isn't long enough.
In particular for iasatty() on arm with tagged pointers.

	David

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