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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>
This commit is contained in:
Eric Dumazet 2015-11-24 11:39:54 -08:00 committed by Linus Torvalds
parent 4ce01c518e
commit 81b1a832d7
1 changed files with 2 additions and 2 deletions
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4
kernel/pid.c
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@ -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();