Hi Jean,

On Fri, Aug 27, 2010 at 02:22:54PM -0700, Jean Tourrilhes wrote:

On Fri, Aug 27, 2010 at 02:02:41PM -0700, Kees Cook wrote:

quoted

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.

quoted

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.

I did not, no. Since I couldn't reproduce the original problem (I lacked
the hardware to test ath5k, and all the other drivers correctly managed
iwp->length).

quoted

[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.

-               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)) {

The comment should probably be clarified -- it's the caller's iwp->length
that may be causing problems (when combined with a driver that forgets to
adjusted iwp->length downward). Regardless, the above patch would appear to
limit the copy_to_user to only the kzalloced region.

Thanks!

-Kees

-- 
Kees Cook
Ubuntu Security Team