noptrace.stp - Disable ptrace from Hierarchies of Processes

    Blocks ptrace(2) attempts from processes identified by stap -c/-x,
    as also specifiable from /proc/systemtap/stap_XXX/ control files.
    Processes may be added or removed from the blocked list.

------------------------------------------------------------------------
Example: block ptrace(2) from a given subprocess hierarchy.

% echo $$
9898

(in other shell)
# stap -g noptrace.stp -x 9898 &

(in original shell)
% strace ls
strace: ptrace(PTRACE_TRACEME, ...): No such process
+++ exited with 1 +++

% bash                      # create a child process 
bash-4.3$ strace ls
strace: ptrace(PTRACE_TRACEME, ...): No such process
+++ exited with 1 +++
bash-4.3$

------------------------------------------------------------------------
Example: block ptrace(2) with a manually managed process list

% echo $$
8282

(in other shell)
# stap -g noptrace.stp &
# cd /proc/systemtap/stap_*
# cat blocked
[empty]
# echo 8282 > block

(in original shell)
% do stuff
% strace ls
[doesn't work]
% do more stuff

(in other shell)
# cat blocked   # child processes
8282
8294
8322
8348

# echo 8282 > unblock

(in original shell)
% strace ls
[now works]