4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
commit dd1c1f2f2028a7b851f701fc6a8ebe39dcb95e7c upstream.
This was reported many times, and this was even mentioned in commit
52ee2dfdd4f5 ("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@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/pid.h | 4 +++-
include/linux/sched.h | 50 +++++++++++++++++++++++++++-----------------------
kernel/pid.c | 11 ++++-------
3 files changed, 34 insertions(+), 31 deletions(-)
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -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
};
/*
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1949,31 +1949,8 @@ static inline pid_t task_tgid_nr(struct
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 int pid_alive(const struct task_struct *p);
-static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
-{
- pid_t pid = 0;
-
- rcu_read_lock();
- if (pid_alive(tsk))
- pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
- rcu_read_unlock();
-
- return pid;
-}
-
-static inline pid_t task_ppid_nr(const struct task_struct *tsk)
-{
- return task_ppid_nr_ns(tsk, &init_pid_ns);
-}
static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk,
struct pid_namespace *ns)
@@ -1998,6 +1975,33 @@ static inline pid_t task_session_vnr(str
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);
+}
+
+static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
+{
+ pid_t pid = 0;
+
+ rcu_read_lock();
+ if (pid_alive(tsk))
+ pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
+ rcu_read_unlock();
+
+ return pid;
+}
+
+static inline pid_t task_ppid_nr(const struct task_struct *tsk)
+{
+ return task_ppid_nr_ns(tsk, &init_pid_ns);
+}
+
/* obsolete, do not use */
static inline pid_t task_pgrp_nr(struct task_struct *tsk)
{
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -526,8 +526,11 @@ pid_t __task_pid_nr_ns(struct task_struc
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(rcu_dereference(task->pids[type].pid), ns);
}
rcu_read_unlock();
@@ -536,12 +539,6 @@ pid_t __task_pid_nr_ns(struct task_struc
}
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));