selinux: selinux_setprocattr()->ptrace_parent() needs rcu_read_lock()
commit c0c1439541f5305b57a83d599af32b74182933fe upstream. selinux_setprocattr() does ptrace_parent(p) under task_lock(p), but task_struct->alloc_lock doesn't pin ->parent or ->ptrace, this looks confusing and triggers the "suspicious RCU usage" warning because ptrace_parent() does rcu_dereference_check(). And in theory this is wrong, spin_lock()->preempt_disable() doesn't necessarily imply rcu_read_lock() we need to access the ->parent. Reported-by: Evan McNabb <emcnabb@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul Moore <pmoore@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -5454,11 +5454,11 @@ static int selinux_setprocattr(struct task_struct *p,
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/* Check for ptracing, and update the task SID if ok.
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Otherwise, leave SID unchanged and fail. */
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ptsid = 0;
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task_lock(p);
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rcu_read_lock();
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tracer = ptrace_parent(p);
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if (tracer)
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ptsid = task_sid(tracer);
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task_unlock(p);
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rcu_read_unlock();
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if (tracer) {
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error = avc_has_perm(ptsid, sid, SECCLASS_PROCESS,
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