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

Jean Tourrilhes
2010-08-27T21:29:08Z

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@hpl.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;
}