Messages in this thread | | | Date | Sat, 31 Aug 2013 21:26:37 +0100 | From | Djalal Harouni <> | Subject | Re: [PATCH 1/2] procfs: restore 0400 permissions on /proc/*/{syscall,stack,personality} |
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(Sorry for my late response)
On Thu, Aug 29, 2013 at 03:14:32PM -0700, Kees Cook wrote: > On Thu, Aug 29, 2013 at 2:11 AM, Djalal Harouni <tixxdz@opendz.org> wrote: > > Hi Eric, > > > > On Wed, Aug 28, 2013 at 05:26:56PM -0700, Eric W. Biederman wrote: > >> > >> I have take a moment and read this thread, and have been completely > >> unenlightend. People are upset but it is totally unclear why. > >> > >> There is no explanation why it is ok to ignore the suid-exec case, as > >> the posted patches do. Which ultimately means the patches provide > > Please, did you take a look at the patches ? > > - INF("syscall", S_IRUGO, proc_pid_syscall), > > + INF("syscall", S_IRUSR, proc_pid_syscall), > > > > Can you please tell me how did you come to the conclusion that the > > patches "ignore the suid-exec case as the posted patches do" ? > > There are a few conditions that need to be handled. The original fix > that Al landed was to stop this: > > create IPC > fork child > child opens /proc/self/syscall > child sends fd to parent over IPC > child execs setuid process > parent reads setuid process's "syscall" file > > The solution was to check perms of reader (in this case parent wasn't > privileged, so it gets denied). Yes, of course
> The new problem is: > > open /proc/$target/syscall > dup to stdin > exec setuid process that reports contents of stdin > > So, changing perms to 0400 doesn't actually fix what we want to fix, > since it can still by bypassed under more limited situations: > > open /proc/self/syscall > dup to stdin > exec setuid process that reports contents of stdin > > So, changing to 0400 means only setuid programs that aren't already > running will have their ASLR leaked. Yes I do realize. That change was only to block leaks against already running processes and *restore* the old permissions.
> [...] > Maybe I'm lacking imagination, but changing to 0400 does reduce the > scope of the leak from all processes to "just" what was execed. This > still needs to be addressed, but I don't see a way to handle this > without explicitly invalidating the /proc handle across exec. Yes Kees,
I did try a year ago to adapt the exec_id from grsecurity and failed (and failed again to resend - not enough resources): https://lkml.org/lkml/2012/3/10/174
Kees IMHO the right solution is to invalidate the fd across exec as you suggest
Alan Cox's thread which describe the problem correctly: https://lkml.org/lkml/2012/1/29/35
Alan suggested to revoke() the file handles.
So: There are more of these /proc files with 0444 and without appropriate ptrace protections that allow ASLR leaks, and doing 0400 will not totally fix it, not to mention that 0400 on /proc/pid/maps can break glibc, etc.
A solution would be to implement the per-cpu exec_id used in grsecurity and also suggested here: https://lkml.org/lkml/2012/3/11/23
grsecurity uses the current (reader) exec_id to track if this is still the same reader. We can use the target exec_id instead of the reader to bind all these files to their exec_id target task + ptrace checkes at open(), read(), write()...
Can we consider this some sort of a revoke() for these special files?
Thanks
-- Djalal Harouni http://opendz.org
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