[tor-bugs] #9249 [Tor]: GSOC seccomp stage 2

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#9249: GSOC seccomp stage 2
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     Reporter:  ctoader      |      Owner:  nickm
         Type:  enhancement  |     Status:  needs_revision
     Priority:  normal       |  Milestone:
    Component:  Tor          |    Version:
   Resolution:               |   Keywords:  tor-relay gsoc seccomp sandbox
Actual Points:               |  Parent ID:  #5756
       Points:               |
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Comment (by nickm):

 Replying to [comment:16 nickm]:
 > But hm.  What happens if somebody tries to mprotect the page right
 before immediately before the mapping, and they give a bunch of pages that
 includes the mapping, as in "mprotect(pr_mem_base - 4096, 8192,
 PROT_READ|PROT_WRITE)" ?
 >
 >
 > (What exactly is it that needs to do mprotect(PROT_READ|PROT_WRITE)? I
 think it is malloc/arena.c in glibc.)

 It appears that the largest arena that glibc will allocate now is 1 MB
 long.  So I believe that we could kludge our way around this by mmaping a
 region that is 1MB larger than we need, putting our constant data at the
 end of it, and forbidding any attempt to mprotect(PROT_READ|PROT_WRITE)
 more than 1MB of data.

 Is there a better kludge?

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9249#comment:17>
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