From: Eric Dumazet <[email protected]>
I got a crash during a "perf top" session that was caused
by a race in __task_pid_nr_ns() :
pid_nr_ns() was inlined, but apparently compiler chose to read
task->pids[type].pid twice, and the pid->level dereference
crashed because we got a NULL pointer at the second read :
if (pid && ns->level <= pid->level) { // CRASH
Just use RCU API properly to solve this race, and not worry
about "perf top" crashing hosts :(
get_task_pid() can benefit from same fix.
Signed-off-by: Eric Dumazet <[email protected]>
---
kernel/pid.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/pid.c b/kernel/pid.c
index ca368793808e..78b3d9f80d44 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -467,7 +467,7 @@ struct pid *get_task_pid(struct task_struct *task, enum
pid_type type)
rcu_read_lock();
if (type != PIDTYPE_PID)
task = task->group_leader;
- pid = get_pid(task->pids[type].pid);
+ pid = get_pid(rcu_dereference(task->pids[type].pid));
rcu_read_unlock();
return pid;
}
@@ -528,7 +528,7 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum
pid_type type,
if (likely(pid_alive(task))) {
if (type != PIDTYPE_PID)
task = task->group_leader;
- nr = pid_nr_ns(task->pids[type].pid, ns);
+ nr = pid_nr_ns(rcu_dereference(task->pids[type].pid), ns);
}
rcu_read_unlock();
--
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