Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless

[Pavel Emelyanov <xemul@openvz.org>]

Oleg Nesterov wrote:
> Without rcu/tasklist/siglock lock task_pid_nr_ns() may read the freed memory,
> move the callsite under ->siglock.
> 
> Sadly, we can report pid == 0 if the task was detached.
>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Acked-by: Pavel Emelyanov <xemul@openvz.org>

> --- 24/fs/proc/array.c~dtst	2007-11-09 12:57:30.000000000 +0300
> +++ 24/fs/proc/array.c	2007-11-17 21:26:55.000000000 +0300
> @@ -392,7 +392,7 @@ static int do_task_stat(struct task_stru
>  	sigset_t sigign, sigcatch;
>  	char state;
>  	int res;
> -	pid_t ppid = 0, pgid = -1, sid = -1;
> +	pid_t pid = 0, ppid = 0, pgid = -1, sid = -1;
>  	int num_threads = 0;
>  	struct mm_struct *mm;
>  	unsigned long long start_time;
> @@ -403,9 +403,6 @@ static int do_task_stat(struct task_stru
>  	unsigned long rsslim = 0;
>  	char tcomm[sizeof(task->comm)];
>  	unsigned long flags;
> -	struct pid_namespace *ns;
> -
> -	ns = current->nsproxy->pid_ns;
>  
>  	state = *get_task_state(task);
>  	vsize = eip = esp = 0;
> @@ -425,6 +422,7 @@ static int do_task_stat(struct task_stru
>  
>  	rcu_read_lock();
>  	if (lock_task_sighand(task, &flags)) {
> +		struct pid_namespace *ns = current->nsproxy->pid_ns;
>  		struct signal_struct *sig = task->signal;
>  
>  		if (sig->tty) {
> @@ -461,6 +459,7 @@ static int do_task_stat(struct task_stru
>  			gtime = cputime_add(gtime, sig->gtime);
>  		}
>  
> +		pid = task_pid_nr_ns(task, ns);
>  		sid = task_session_nr_ns(task, ns);
>  		pgid = task_pgrp_nr_ns(task, ns);
>  		ppid = task_ppid_nr_ns(task, ns);
> @@ -495,7 +494,7 @@ static int do_task_stat(struct task_stru
>  	res = sprintf(buffer, "%d (%s) %c %d %d %d %d %d %u %lu \
>  %lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
>  %lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld\n",
> -		task_pid_nr_ns(task, ns),
> +		pid,
>  		tcomm,
>  		state,
>  		ppid,
> 
> 

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