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

From: Johannes Berg <[email-masked]>
Date: Thu, 13 Sep 2018 14:16:45 +0200

On Thu, 2018-09-13 at 13:13 +0100, Al Viro wrote:
> On Thu, Sep 13, 2018 at 01:49:09PM +0200, Johannes Berg wrote:
> > From: Johannes Berg <[email-masked]>
> > 
> > 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...

Yeah, that's a bit better perhaps, I should resend to have the bugzilla
link anyway.

johannes