linux-kernel - [005/197] oom: fix the unsafe usage of badness() in proc_oom

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Message-Id: <20100422190907.864799567@kvm.kroah.org>
Date:	Thu, 22 Apr 2010 12:07:36 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Oleg Nesterov <oleg@...hat.com>
Subject: [005/197] oom: fix the unsafe usage of badness() in proc_oom_score()

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

commit b95c35e76b29ba812e5dabdd91592e25ec640e93 upstream.

proc_oom_score(task) has a reference to task_struct, but that is all.
If this task was already released before we take tasklist_lock

	- we can't use task->group_leader, it points to nowhere

	- it is not safe to call badness() even if this task is
	  ->group_leader, has_intersects_mems_allowed() assumes
	  it is safe to iterate over ->thread_group list.

	- even worse, badness() can hit ->signal == NULL

Add the pid_alive() check to ensure __unhash_process() was not called.

Also, use "task" instead of task->group_leader. badness() should return
the same result for any sub-thread. Currently this is not true, but
this should be changed anyway.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/proc/base.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -442,12 +442,13 @@ static const struct file_operations proc
 unsigned long badness(struct task_struct *p, unsigned long uptime);
 static int proc_oom_score(struct task_struct *task, char *buffer)
 {
-	unsigned long points;
+	unsigned long points = 0;
 	struct timespec uptime;
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	read_lock(&tasklist_lock);
-	points = badness(task->group_leader, uptime.tv_sec);
+	if (pid_alive(task))
+		points = badness(task, uptime.tv_sec);
 	read_unlock(&tasklist_lock);
 	return sprintf(buffer, "%lu\n", points);
 }


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