From 81b1a832d79749058863cffe2c0ed4ef40f6e6ec Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 24 Nov 2015 11:39:54 -0800 Subject: [PATCH] pidns: fix NULL dereference in __task_pid_nr_ns() 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 Signed-off-by: Linus Torvalds --- 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(); -- 2.39.2