netdev - Re: [PATCH] wireless: fix 64K kernel heap content leak via ioctl

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Date:	Fri, 27 Aug 2010 14:22:54 -0700
From:	Jean Tourrilhes <jt@....hp.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Johannes Berg <johannes@...solutions.net>,
	Joe Perches <joe@...ches.com>, Tejun Heo <tj@...nel.org>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] wireless: fix 64K kernel heap content leak via ioctl

On Fri, Aug 27, 2010 at 02:02:41PM -0700, Kees Cook wrote:
> This problem was originally tracked down by Brad Spengler.
> 
> When calling wireless ioctls, if a driver does not correctly
> validate/shrink iwp->length, the resulting copy_to_user can leak up to
> 64K of kernel heap contents.
> 
> It seems that this is triggerable[1] in 2.6.32 at least on ath5k, but
> I was not able to track down how. The twisty maze of ioctl handlers
> stumped me. :)

	You can always ask.

> Other drivers I checked did not appear to have any problems,
> but the potential remains. I'm not sure if this patch is the right approach;
> it was fixed differently[2] in grsecurity.

	Did you tried your patch for real ? With large scan request ?
	I ask because at first glance, it looks incorrect, asI believe
it kills large request. But someone would need to test, for sure.

> [1] http://forums.grsecurity.net/viewtopic.php?f=3&t=2290&start=0
> [2] http://grsecurity.net/~spender/wireless-infoleak-fix2.patch

	I believe this patch would make the situation worse.

	Would you mind validating the following patch ? I've just
verified that it compiles and I believe it does what you are asking in
a much more predictable way.
	Regards,

	Jean

Signed-off-by: Jean Tourrilhes <jt@....hp.com>

diff -u -p wext.j2.c wext.c
--- wext.j2.c   2010-08-27 14:17:26.000000000 -0700
+++ wext.c      2010-08-27 14:19:33.000000000 -0700
@@ -800,9 +800,12 @@ static int ioctl_standard_iw_point(struc
                        goto out;
                }
 
-               if (copy_to_user(iwp->pointer, extra,
-                                iwp->length *
-                                descr->token_size)) {
+               /* Verify how much we should return. Some driver
+                * may abuse iwp->length... */
+               if((iwp->length * descr->token_size) < extra_size)
+                       extra_size = iwp->length * descr->token_size;
+
+               if (copy_to_user(iwp->pointer, extra, extra_size)) {
                        err = -EFAULT;
                        goto out;
                }
--
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