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SubjectRe: [PATCH] pidhash: Kill switch_exec_pids
Eric W. Biederman wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -699,7 +699,17 @@ static int de_thread(struct task_struct
> remove_parent(current);
> remove_parent(leader);
>
> - switch_exec_pids(leader, current);
> +
> + /* Become a process group leader with the old leader's pid.
> + * Note: The old leader also uses thispid until release_task
> + * is called. Odd but simple and correct.
> + */
> + detach_pid(current, PIDTYPE_PID);
> + current->pid = leader->pid;
> + attach_pid(current, PIDTYPE_PID, current->pid);

What happens after de_thread() unlocks tasklist_lock and before
it is taken again in release_task() ?

In that window find_task_by_pid() will return dead leader, not
the new leader of thread group. This means we can miss tkill()
or ptrace(), for example.

Oleg.
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