kernel/fork.c:copy_process(): don't add the uninitialized child to thread/task/pid lists
copy_process() adds the new child to thread_group/init_task.tasks list and then does attach_pid(child, PIDTYPE_PID). This means that the lockless next_thread() or next_task() can see this thread with the wrong pid. Say, "ls /proc/pid/task" can list the same inode twice. We could move attach_pid(child, PIDTYPE_PID) up, but in this case find_task_by_vpid() can find the new thread before it was fully initialized. And this is already true for PIDTYPE_PGID/PIDTYPE_SID, With this patch copy_process() initializes child->pids[*].pid first, then calls attach_pid() to insert the task into the pid->tasks list. attach_pid() no longer need the "struct pid*" argument, it is always called after pid_link->pid was already set. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Sergey Dyasly <dserrg@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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80628ca06c
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8190773985
@ -86,11 +86,9 @@ extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
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extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
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/*
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* attach_pid() and detach_pid() must be called with the tasklist_lock
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* write-held.
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* these helpers must be called with the tasklist_lock write-held.
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*/
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extern void attach_pid(struct task_struct *task, enum pid_type type,
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struct pid *pid);
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extern void attach_pid(struct task_struct *task, enum pid_type);
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extern void detach_pid(struct task_struct *task, enum pid_type);
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extern void change_pid(struct task_struct *task, enum pid_type,
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struct pid *pid);
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@ -1121,6 +1121,12 @@ static void posix_cpu_timers_init(struct task_struct *tsk)
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INIT_LIST_HEAD(&tsk->cpu_timers[2]);
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}
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static inline void
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init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
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{
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task->pids[type].pid = pid;
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}
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/*
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* This creates a new process as a copy of the old one,
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* but does not actually start it yet.
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@ -1449,7 +1455,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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if (likely(p->pid)) {
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ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
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init_task_pid(p, PIDTYPE_PID, pid);
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if (thread_group_leader(p)) {
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init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
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init_task_pid(p, PIDTYPE_SID, task_session(current));
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if (is_child_reaper(pid)) {
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ns_of_pid(pid)->child_reaper = p;
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p->signal->flags |= SIGNAL_UNKILLABLE;
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@ -1457,10 +1467,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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p->signal->leader_pid = pid;
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p->signal->tty = tty_kref_get(current->signal->tty);
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attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
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attach_pid(p, PIDTYPE_SID, task_session(current));
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list_add_tail(&p->sibling, &p->real_parent->children);
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list_add_tail_rcu(&p->tasks, &init_task.tasks);
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attach_pid(p, PIDTYPE_PGID);
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attach_pid(p, PIDTYPE_SID);
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__this_cpu_inc(process_counts);
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} else {
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current->signal->nr_threads++;
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@ -1470,7 +1480,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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list_add_tail_rcu(&p->thread_group,
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&p->group_leader->thread_group);
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}
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attach_pid(p, PIDTYPE_PID, pid);
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attach_pid(p, PIDTYPE_PID);
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nr_threads++;
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}
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12
kernel/pid.c
12
kernel/pid.c
@ -373,14 +373,10 @@ EXPORT_SYMBOL_GPL(find_vpid);
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/*
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* attach_pid() must be called with the tasklist_lock write-held.
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*/
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void attach_pid(struct task_struct *task, enum pid_type type,
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struct pid *pid)
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void attach_pid(struct task_struct *task, enum pid_type type)
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{
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struct pid_link *link;
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link = &task->pids[type];
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link->pid = pid;
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hlist_add_head_rcu(&link->node, &pid->tasks[type]);
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struct pid_link *link = &task->pids[type];
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hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
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}
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static void __change_pid(struct task_struct *task, enum pid_type type,
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@ -412,7 +408,7 @@ void change_pid(struct task_struct *task, enum pid_type type,
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struct pid *pid)
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{
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__change_pid(task, type, pid);
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attach_pid(task, type, pid);
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attach_pid(task, type);
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}
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/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
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