Code:  unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
 		      const nodemask_t *nodemask, unsigned long totalpages)
 {
	int points;
 
 	if (oom_unkillable_task(p, mem, nodemask))
 		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	/*
	 * Shortcut check for a thread sharing p->mm that is OOM_SCORE_ADJ_MIN
	 * so the entire heuristic doesn't need to be executed for something
	 * that cannot be killed.
	 */
	if (atomic_read(&p->mm->oom_disable_count)) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The memory controller may have a limit of 0 bytes, so avoid a divide
	 * by zero, if necessary.
	 */
	if (!totalpages)
		totalpages = 1;

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + p->mm->nr_ptes;
	points += get_mm_counter(p->mm, MM_SWAPENTS);

	points *= 1000;
	points /= totalpages;
	task_unlock(p);

	/*
	 * Root processes get 3% bonus, just like the __vm_enough_memory()
	 * implementation used by LSMs.
	 */
	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
		points -= 30;

	/*
	 * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
	 * either completely disable oom killing or always prefer a certain
	 * task.
	 */
	points += p->signal->oom_score_adj;

	/*
	 * Never return 0 for an eligible task that may be killed since it's
	 * possible that no single user task uses more than 0.1% of memory and
	 * no single admin tasks uses more than 3.0%.
	 */
	if (points <= 0)
		return 1;
	return (points < 1000) ? points : 1000;
}

Vulnerability Type: DoS Overflow 
CWE ID: CWE-189
Summary: Integer overflow in the oom_badness function in mm/oom_kill.c in the Linux kernel before 3.1.8 on 64-bit platforms allows local users to cause a denial of service (memory consumption or process termination) by using a certain large amount of memory.
Commit Message: oom: fix integer overflow of points in oom_badness

commit ff05b6f7ae762b6eb464183eec994b28ea09f6dd upstream.

An integer overflow will happen on 64bit archs if task's sum of rss,
swapents and nr_ptes exceeds (2^31)/1000 value.  This was introduced by
commit

f755a04 oom: use pte pages in OOM score

where the oom score computation was divided into several steps and it's no
longer computed as one expression in unsigned long(rss, swapents, nr_pte
are unsigned long), where the result value assigned to points(int) is in
range(1..1000).  So there could be an int overflow while computing

176          points *= 1000;

and points may have negative value. Meaning the oom score for a mem hog task
will be one.

196          if (points <= 0)
197                  return 1;

For example:
[ 3366]     0  3366 35390480 24303939   5       0             0 oom01
Out of memory: Kill process 3366 (oom01) score 1 or sacrifice child

Here the oom1 process consumes more than 24303939(rss)*4096~=92GB physical
memory, but it's oom score is one.

In this situation the mem hog task is skipped and oom killer kills another and
most probably innocent task with oom score greater than one.

The points variable should be of type long instead of int to prevent the
int overflow.

Signed-off-by: Frantisek Hrbata <fhrbata@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>