On Thu, Sep 29, 2016 at 01:32:56AM +0200, Jann Horn wrote: > On Wed, Sep 28, 2016 at 04:22:53PM -0700, Andy Lutomirski wrote: > > On Wed, Sep 28, 2016 at 3:54 PM, Jann Horn <jann@xxxxxxxxx> wrote: > > > SELinux attempts to make it possible to whitelist trustworthy sources of > > > code that may be mapped into memory, and Android makes use of this feature. > > > To prevent an attacker from bypassing this by modifying R+X memory through > > > /proc/$pid/mem or PTRACE_POKETEXT, it is necessary to call a security hook > > > in check_vma_flags(). > > > > If selinux policy allows PTRACE_POKETEXT, is it really so bad for that > > to result in code execution? > > Have a look at __ptrace_may_access(): > > /* Don't let security modules deny introspection */ > if (same_thread_group(task, current)) > return 0; > > This means thread A can attach to thread B and poke its memory, and SELinux > can't do anything about it. > > I guess another perspective on this would be that it's a problem that > interfaces usable for poking user memory are subject to introspection rules > (as opposed to e.g. /proc/self/maps, where it is actually useful). Ugh, I'm talking nonsense, ptrace() doesn't work on threads. (/proc/$pid/mem works though). And then, ptrace-ish APIs aside, there are those weird devices that do DMA with force=1.
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