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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>
This commit is contained in:
Oleg Nesterov 2013-07-03 15:08:31 -07:00 committed by syphyr
parent 71cf620d99
commit 31bbe17032
3 changed files with 19 additions and 15 deletions
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6
include/linux/pid.h
View File

@ -88,11 +88,9 @@ extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
/*
* attach_pid() and detach_pid() must be called with the tasklist_lock
* write-held.
* these helpers must be called with the tasklist_lock write-held.
*/
extern void attach_pid(struct task_struct *task, enum pid_type type,
struct pid *pid);
extern void attach_pid(struct task_struct *task, enum pid_type);
extern void detach_pid(struct task_struct *task, enum pid_type);
extern void change_pid(struct task_struct *task, enum pid_type,
struct pid *pid);

16
kernel/fork.c
View File

@ -1188,6 +1188,12 @@ static void posix_cpu_timers_init(struct task_struct *tsk)
INIT_LIST_HEAD(&tsk->cpu_timers[2]);
}
static inline void
init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
{
task->pids[type].pid = pid;
}
/*
* This creates a new process as a copy of the old one,
* but does not actually start it yet.
@ -1536,7 +1542,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if (likely(p->pid)) {
ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
init_task_pid(p, PIDTYPE_PID, pid);
if (thread_group_leader(p)) {
init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
init_task_pid(p, PIDTYPE_SID, task_session(current));
if (is_child_reaper(pid)) {
ns_of_pid(pid)->child_reaper = p;
p->signal->flags |= SIGNAL_UNKILLABLE;
@ -1544,10 +1554,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->signal->leader_pid = pid;
p->signal->tty = tty_kref_get(current->signal->tty);
attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
attach_pid(p, PIDTYPE_SID, task_session(current));
list_add_tail(&p->sibling, &p->real_parent->children);
list_add_tail_rcu(&p->tasks, &init_task.tasks);
attach_pid(p, PIDTYPE_PGID);
attach_pid(p, PIDTYPE_SID);
__this_cpu_inc(process_counts);
} else {
current->signal->nr_threads++;
@ -1558,7 +1568,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
list_add_tail_rcu(&p->thread_node,
&p->signal->thread_head);
}
attach_pid(p, PIDTYPE_PID, pid);
attach_pid(p, PIDTYPE_PID);
nr_threads++;
}

12
kernel/pid.c
View File

@ -382,14 +382,10 @@ EXPORT_SYMBOL_GPL(find_vpid);
/*
* attach_pid() must be called with the tasklist_lock write-held.
*/
void attach_pid(struct task_struct *task, enum pid_type type,
struct pid *pid)
void attach_pid(struct task_struct *task, enum pid_type type)
{
struct pid_link *link;
link = &task->pids[type];
link->pid = pid;
hlist_add_head_rcu(&link->node, &pid->tasks[type]);
struct pid_link *link = &task->pids[type];
hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
}
static void __change_pid(struct task_struct *task, enum pid_type type,
@ -421,7 +417,7 @@ void change_pid(struct task_struct *task, enum pid_type type,
struct pid *pid)
{
__change_pid(task, type, pid);
attach_pid(task, type, pid);
attach_pid(task, type);
}
/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */