[Bug server/30453] gdbserver cannot set breakpoints when /proc/pid/mem is not writable

["manojgupta at google dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30453

--- Comment #3 from Manoj Gupta <manojgupta at google dot com> ---
Unfortunately, writes to /proc/pid/mem has been disabled for a long time as
part of security hardening as it has been used in security expolits. Please
feel free to check the bugs
https://bugs.chromium.org/p/chromium/issues/detail?id=766253 and
https://bugs.chromium.org/p/chromium/issues/detail?id=781376 . 

Ptrace is also discussed in that bug. It is lesser of an issue because the
devices use seccomp filters for most critical and do not allow ptrace syscall
to be used.


```
sure, if you have ptrace scope on a process, it def leaves it open to arbitrary
read/writes of any memory region.  the difference there is that it requires you
to be within a specific scope (as you noted), and you need to be able to access
the ptrace syscall.  that's a much higher barrier than accessing the "mem" file
which can be hit with a simple `dd` fork+exec.

when it comes to seccomp filters, we have the ability to run daemons/processes
through restrictive syscall filters, and we have yet to include ptrace there. 
off the top of my head, the only valid use of ptrace on the system is in
upstart itself (which uses it for process tracking).  it might be interesting
to severely restrict ptrace so only pid 1 (init) is allowed to use it.
```

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