[PATCH 4/5] mempolicy: fix refcount leak in mpol_set_shared_policy()

[Mel Gorman]

From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>

When shared_policy_replace() fails to allocate new->policy is not freed
correctly by mpol_set_shared_policy().  The problem is that shared mempolicy
code directly call kmem_cache_free() in multiple places where it is easy
to make a mistake.

This patch creates an sp_free wrapper function and uses it. The bug was
introduced pre-git age (IOW, before 2.6.12-rc2).

[mgorman@xxxxxxx: Editted changelog]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/mempolicy.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d297929..45f9825 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2157,12 +2157,17 @@ mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
 	return pol;
 }
 
+static void sp_free(struct sp_node *n)
+{
+	mpol_put(n->policy);
+	kmem_cache_free(sn_cache, n);
+}
+
 static void sp_delete(struct shared_policy *sp, struct sp_node *n)
 {
 	pr_debug("deleting %lx-l%lx\n", n->start, n->end);
 	rb_erase(&n->nd, &sp->root);
-	mpol_put(n->policy);
-	kmem_cache_free(sn_cache, n);
+	sp_free(n);
 }
 
 static struct sp_node *sp_alloc(unsigned long start, unsigned long end,
@@ -2301,7 +2306,7 @@ int mpol_set_shared_policy(struct shared_policy *info,
 	}
 	err = shared_policy_replace(info, vma->vm_pgoff, vma->vm_pgoff+sz, new);
 	if (err && new)
-		kmem_cache_free(sn_cache, new);
+		sp_free(new);
 	return err;
 }
 
@@ -2318,9 +2323,7 @@ void mpol_free_shared_policy(struct shared_policy *p)
 	while (next) {
 		n = rb_entry(next, struct sp_node, nd);
 		next = rb_next(&n->nd);
-		rb_erase(&n->nd, &p->root);
-		mpol_put(n->policy);
-		kmem_cache_free(sn_cache, n);
+		sp_delete(p, n);
 	}
 	mutex_unlock(&p->mutex);
 }
-- 
1.7.7

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