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Subject[RFC PATCH 01/12 v3] ptrace: ptrace_signal: fix the usage of ->parent
This patch complicates the code to fix the pure theoretical problems.
But since we are going to change this code, it is better to fix them
anyway.

- If we are not traced any longer after ptrace_stop(), si_pid/si_uid
are not necessary right.

- It is not safe to dereference current->parent without tasklist or
RCU lock. The tracer can detach and exit. ->siglock can't prevent
this, and (in theory) local_irq_disable() doesn't imply RCU lock.

Hopefully this "signr != info->si_signo" code will go away eventually.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

kernel/signal.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

--- PTRACE/kernel/signal.c~01_PTRACE_SIGNAL 2009-05-30 21:30:04.000000000 +0200
+++ PTRACE/kernel/signal.c 2009-05-30 21:52:00.000000000 +0200
@@ -1770,11 +1770,22 @@ static int ptrace_signal(int signr, sigi
specific in the siginfo structure then it should
have updated *info via PTRACE_SETSIGINFO. */
if (signr != info->si_signo) {
+ struct task_struct *tracer;
+
info->si_signo = signr;
info->si_errno = 0;
info->si_code = SI_USER;
- info->si_pid = task_pid_vnr(current->parent);
- info->si_uid = task_uid(current->parent);
+
+ rcu_read_lock();
+ tracer = current->parent;
+ if (task_ptrace(current)) {
+ info->si_pid = task_pid_vnr(tracer);
+ info->si_uid = task_uid(tracer);
+ } else {
+ info->si_pid = 0;
+ info->si_uid = 0;
+ }
+ rcu_read_unlock();
}

/* If the (new) signal is now blocked, requeue it. */


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