Date: Thu, 6 Jun 2013 15:02:33 -0700 From: Greg KH <greg@...ah.com> To: oss-security@...ts.openwall.com Subject: Re: Linux kernel format string flaws On Thu, Jun 06, 2013 at 01:59:55PM -0700, Kees Cook wrote: > I've found two issues in how Linux uses format strings: > > > CVE-2013-2852: b43 wireless driver > > The b43 driver reports error strings that can be interpreted as format > strings. Under normal conditions, this is not a problem, but it is > possible for the "fwpostfix" module parameter to change the filenames > used to fetch firmware. When such a file is not found, the filename > will be processed as a format string. This flaw could potentially allow > escalation from uid-0 to ring-0, so except for certain environments, > it is not too serious. > > If b43 hardware is available, this should show itself easily. I don't have > any available for testing, but it seems it would show itself like this: > # rmmod b43 > # modprobe b43 fwpostfix=AA%xBB > ... > # dmesg > ... > b43-0 ERROR: Firmware file "b43AAdeff80ccBB/a0g1bsinitvals5.fw" not found > > Using %n instead of %x would lead to exciting crashes. :) > > It has been fixed in the upstream wireless tree: > > http://git.kernel.org/cgit/linux/kernel/git/linville/wireless.git/commit/?id=9538cbaab6e8b8046039b4b2eb6c9d614dc782bd > > > CVE-2013-2851: block layer > > The block layer uses the "disk_name" field as a format > string in a number of places. While this is normally not a problem due > to how disk names are created (statically or incrementally), there > is currently at least one way to define nearly arbitrary names via > md. Instead of filtering md, this should be fixed within the kernel's > interfaces. This flaw could potentially allow escalation from uid-0 to > ring-0, so except for certain environments, it is not too serious. > > The test case is trivial: > # echo md_%x.%x.%x.%x > /sys/module/md_mod/parameters/new_array > # ls /dev/md_* > /dev/md_c12cc370.df66d800.df66d80c.c13da45b > > Using %n instead of %x leads to exciting crashes. :) > > The fix has been sent upstream: > http://marc.info/?l=linux-kernel&m=137055204522556&w=2 > > > With the above fixes, a series of additional format string related clean > ups has also been sent upstream: > http://marc.info/?l=linux-kernel&m=137055207522563&w=2 For both of these, you have to have root permissions in order to cause any problems, right? thanks, greg k-h
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