Return-path: Received: from smtp.outflux.net ([198.145.64.163]:51423 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752580Ab0H0VpH (ORCPT ); Fri, 27 Aug 2010 17:45:07 -0400 Date: Fri, 27 Aug 2010 14:43:57 -0700 From: Kees Cook To: Jean Tourrilhes Cc: linux-kernel@vger.kernel.org, "John W. Linville" , "David S. Miller" , Eric Dumazet , Johannes Berg , Joe Perches , Tejun Heo , linux-wireless@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH] wireless: fix 64K kernel heap content leak via ioctl Message-ID: <20100827214357.GE4703@outflux.net> References: <20100827210240.GC4703@outflux.net> <20100827212254.GB32275@bougret.hpl.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20100827212254.GB32275@bougret.hpl.hp.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: 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: > > 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. 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). > > [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