netdev - Re: [PATCH] socket: fix struct ifreq size in compat ioctl

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Date:   Thu, 13 Sep 2018 13:13:53 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     netdev@...r.kernel.org, Robert O'Callahan <robert@...llahan.org>,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH] socket: fix struct ifreq size in compat ioctl

On Thu, Sep 13, 2018 at 01:49:09PM +0200, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> As reported by Reobert O'Callahan, since Viro's commit to kill
> dev_ifsioc() we attempt to copy too much data in compat mode,
> which may lead to EFAULT when the 32-bit version of struct ifreq
> sits at/near the end of a page boundary, and the next page isn't
> mapped.
> 
> Fix this by passing whether or not we're doing a compat call and
> copying the appropriate size in/out, as we did before. This works
> because only the embedded "struct ifmap" has different size, and
> this is only used in SIOCGIFMAP/SIOCSIFMAP which has a different
> handler. All other parts of the union are naturally compatible.

Might be better to pass explicit size instead of this bool compat...