[tor-bugs] #22660 [Core Tor/Tor]: Guard against stack smashing attacks in tor

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#22660: Guard against stack smashing attacks in tor
------------------------------+-------------------------------------
     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-hardening, security
Actual Points:                |  Parent ID:
       Points:  0.5           |   Reviewer:
      Sponsor:                |
------------------------------+-------------------------------------
 If we tor with -fstack-check (GCC, it's a no-op in clang[0]), it will
 protect against stack smashing attacks that jump the stack guard page(s):
 {{{
 Recompile all userland code (ld.so, libraries, binaries) with GCC's
   "-fstack-check" option, which prevents the stack-pointer from moving
   into another memory region without accessing the stack guard-page (it
   writes one word to every 4KB page allocated on the stack).
 }}}
 III. Solutions, https://www.qualys.com/2017/06/19/stack-clash/stack-
 clash.txt

 {{{
 -fstack-check
 Generate code to verify that you do not go beyond the boundary of the
 stack. You should specify this flag if you are running in an environment
 with multiple threads, but only rarely need to specify it in a single-
 threaded environment since stack overflow is automatically detected on
 nearly all systems if there is only one stack.
 Note that this switch does not actually cause checking to be done; the
 operating system must do that. The switch causes generation of code to
 ensure that the operating system sees the stack being extended.
 }}}
 http://gcc.gnu.org/onlinedocs/gcc-4.3.6/gcc/Code-Gen-Options.html#Code-
 Gen-Options

 This protects against:
 {{{
 - a local-root exploit against ld.so and most SUID-root binaries
   (CVE-2017-1000366, CVE-2017-1000379) on amd64 Debian, Ubuntu, Fedora,
   CentOS;
 }}}

 There are remote attack possibilities mentioned in the paper as well.

 We might also want to add:
 {{{
 -Wl,-z,noexecstack and -Wl,-z,noexecheap
 }}}
 https://www.owasp.org/index.php/C-Based_Toolchain_Hardening#GCC.2FBinutils

 [0]: for clsng, we could use -fsanitize=safe-stack instead, but that's
 more intrusive: https://blog.quarkslab.com/clang-hardening-cheat-
 sheet.html

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22660>
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