Commit 81b1a832 authored Nov 24, 2015 by Eric Dumazet Committed by Linus Torvalds Nov 24, 2015

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 <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4ce01c51

kernel/pid.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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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