linux-kernel - Re: dev_ifname32() fails on 32->64bit calls in copy_in

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Message-Id: <200710310212.42674.arnd@arndb.de>
Date:	Wed, 31 Oct 2007 02:12:42 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Joel Becker <Joel.Becker@...cle.com>
Cc:	Linux Netdev <linux-netdev@...r.kernel.org>,
	Linux Kernel Mailing List <Linux-Kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: dev_ifname32() fails on 32->64bit calls in copy_in_user().

On Wednesday 31 October 2007, Joel Becker wrote:
> 
>         Instrumenting the kernel with printks, the EFAULT comes from
> the first copy_in_user() at line 325 of fs/compat_ioctl.c (in
> dev_ifname32()).  I put some access_ok() checks in, and they do not
> trigger (access is ok).  The call never even gets into sys_ioctl().

Can you printk the pointers (arg and uifr) as well? Maybe the end up
unaligned or otherwise corrupted for some reason.

Does the same thing happen when you try the ioctl on something that
is not even a socket? E.g.

#include <whatever you need...>
int main(void)
{
	struct ifreq ifr = {};
	ioctl(0 /* standard input! */, SIOCGIFNAME, &ifr);
	perror("ioctl");
}

	Arnd <><
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