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BACKPORT: FROMLIST: pids: make task_tgid_nr_ns() safe

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This was reported many times, and this was even mentioned in commit
52ee2dfdd4 "pids: refactor vnr/nr_ns helpers to make them safe" but
somehow nobody bothered to fix the obvious problem: task_tgid_nr_ns()
is not safe because task->group_leader points to nowhere after the
exiting task passes exit_notify(), rcu_read_lock() can not help.

We really need to change __unhash_process() to nullify group_leader,
parent, and real_parent, but this needs some cleanups. Until then we
can turn task_tgid_nr_ns() into another user of __task_pid_nr_ns() and
fix the problem.

Reported-by: Troy Kensinger <tkensinger@google.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

(url: https://patchwork.kernel.org/patch/9913055/)
Bug: 31495866

Change-Id: I5e67b02a77e805f71fa3a787249f13c1310f02e2
This commit is contained in:
Oleg Nesterov 2017-08-21 17:35:02 +02:00 committed by TALU
parent cd666c6214
commit 2a5d231810
3 changed files with 17 additions and 15 deletions
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4
include/linux/pid.h
View File

@ -8,7 +8,9 @@ enum pid_type
PIDTYPE_PID,
PIDTYPE_PGID,
PIDTYPE_SID,
PIDTYPE_MAX
PIDTYPE_MAX,
/* only valid to __task_pid_nr_ns() */
__PIDTYPE_TGID
};
/*

17
include/linux/sched.h
View File

@ -1693,13 +1693,6 @@ static inline pid_t task_tgid_nr(struct task_struct *tsk)
return tsk->tgid;
}
pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns);
static inline pid_t task_tgid_vnr(struct task_struct *tsk)
{
return pid_vnr(task_tgid(tsk));
}
static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk,
struct pid_namespace *ns)
@ -1724,6 +1717,16 @@ static inline pid_t task_session_vnr(struct task_struct *tsk)
return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
}
static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
return __task_pid_nr_ns(tsk, __PIDTYPE_TGID, ns);
}
static inline pid_t task_tgid_vnr(struct task_struct *tsk)
{
return __task_pid_nr_ns(tsk, __PIDTYPE_TGID, NULL);
}
/* obsolete, do not use */
static inline pid_t task_pgrp_nr(struct task_struct *tsk)
{

11
kernel/pid.c
View File

@ -522,8 +522,11 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
if (!ns)
ns = task_active_pid_ns(current);
if (likely(pid_alive(task))) {
if (type != PIDTYPE_PID)
if (type != PIDTYPE_PID) {
if (type == __PIDTYPE_TGID)
type = PIDTYPE_PID;
task = task->group_leader;
}
nr = pid_nr_ns(task->pids[type].pid, ns);
}
rcu_read_unlock();
@ -532,12 +535,6 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
}
EXPORT_SYMBOL(__task_pid_nr_ns);
pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
return pid_nr_ns(task_tgid(tsk), ns);
}
EXPORT_SYMBOL(task_tgid_nr_ns);
struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
{
return ns_of_pid(task_pid(tsk));