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 -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
