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SubjectRe: [PATCH 3/3] ptrace: do not use task_lock() for attach
* Oleg Nesterov (oleg@redhat.com) wrote:
> + write_lock_irq(&tasklist_lock);
> retval = -EPERM;
> if (unlikely(task->exit_state))
> - goto bad;
> + goto unlock_tasklist;
> if (task->ptrace)
> - goto bad;
> + goto unlock_tasklist;

So, task->ptrace now protected by tasklist_lock to keep concurrent tracers
from both attaching to same task? What does this do for setprocattr()?

task_lock(p);
tracer = tracehook_tracer_task(p);
if (tracer)
ptsid = task_sid(tracer);
task_unlock(p);
Looks like it is racy.

cpu1 (tracer) cpu2 (tracee, changing sid)
------------- ---------------------------
task_lock(tracee);
__ptrace_may_access(tracee, ATTACH);
task_unlock(tracee);
task_lock(tracee)
<security check passes> tracer = tracehook_tracer_task(tracee);
if (tracer) <-- NULL, !tracee->ptrace
...
update sid w/out checking against tracer
write_lock_irq(&tasklist_lock);
...
tracee->ptrace = PT_PTRACED;
...
now we are tracing task w/ a sid
that we didn't authorize to trace
What do you think?

thanks,
-chris


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