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

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From: Oleg Nesterov <oleg@...>
To: Andrew Morton <akpm@...>, Eric W. Biederman <ebiederm@...>, Pavel Emelyanov <xemul@...>
Cc: <linux-kernel@...>
Subject: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless
Date: Saturday, November 17, 2007 - 2:31 pm

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>

--- 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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Messages in current thread:
[PATCH] do_task_stat: don't use task_pid_nr_ns() lockless, Oleg Nesterov, (Sat Nov 17, 2:31 pm)
[PATCH] proc: Proper pidns handling for /proc/self, Eric W. Biederman, (Mon Nov 19, 6:30 pm)
Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless, Eric W. Biederman, (Sat Nov 17, 4:11 pm)
Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless, Pavel Emelyanov, (Mon Nov 19, 5:30 am)
Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless, Eric W. Biederman, (Mon Nov 19, 2:04 pm)
[PATCH 0/4] proc: Cleanup status files., Eric W. Biederman, (Mon Nov 19, 5:59 pm)
Re: [PATCH 0/4] proc: Cleanup status files., Pavel Emelyanov, (Tue Nov 20, 6:34 am)
[PATCH 1/4] proc: Implement proc_single_file_operations, Eric W. Biederman, (Mon Nov 19, 6:04 pm)
[PATCH 2/4] proc: Rewrite do_task_stat to correctly handle p..., Eric W. Biederman, (Mon Nov 19, 6:06 pm)
[PATCH 3/4] proc: seqfile convert proc_pid_status to properl..., Eric W. Biederman, (Mon Nov 19, 6:10 pm)
[PATCH] proc: seqfile convert proc_pid_statm, Eric W. Biederman, (Mon Nov 19, 6:13 pm)
Re: [PATCH] do_task_stat: don't use task_pid_nr_ns() lockless, Pavel Emelyanov, (Mon Nov 19, 5:31 am)