[PATCH 2/5] mm: convert anon_vma.refcount from atomic_t to refcount_t

From: Elena Reshetova
Date: Mon Feb 20 2017 - 05:49:35 EST


refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
include/linux/rmap.h | 7 ++++---
mm/rmap.c | 14 +++++++-------
2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 8c89e90..a8f4a97 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -10,6 +10,7 @@
#include <linux/rwsem.h>
#include <linux/memcontrol.h>
#include <linux/highmem.h>
+#include <linux/refcount.h>

/*
* The anon_vma heads a list of private "related" vmas, to scan if
@@ -35,7 +36,7 @@ struct anon_vma {
* the reference is responsible for clearing up the
* anon_vma if they are the last user on release
*/
- atomic_t refcount;
+ refcount_t refcount;

/*
* Count of child anon_vmas and VMAs which points to this anon_vma.
@@ -102,14 +103,14 @@ enum ttu_flags {
#ifdef CONFIG_MMU
static inline void get_anon_vma(struct anon_vma *anon_vma)
{
- atomic_inc(&anon_vma->refcount);
+ refcount_inc(&anon_vma->refcount);
}

void __put_anon_vma(struct anon_vma *anon_vma);

static inline void put_anon_vma(struct anon_vma *anon_vma)
{
- if (atomic_dec_and_test(&anon_vma->refcount))
+ if (refcount_dec_and_test(&anon_vma->refcount))
__put_anon_vma(anon_vma);
}

diff --git a/mm/rmap.c b/mm/rmap.c
index 8774791..3321c86 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -77,7 +77,7 @@ static inline struct anon_vma *anon_vma_alloc(void)

anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
if (anon_vma) {
- atomic_set(&anon_vma->refcount, 1);
+ refcount_set(&anon_vma->refcount, 1);
anon_vma->degree = 1; /* Reference for first vma */
anon_vma->parent = anon_vma;
/*
@@ -92,7 +92,7 @@ static inline struct anon_vma *anon_vma_alloc(void)

static inline void anon_vma_free(struct anon_vma *anon_vma)
{
- VM_BUG_ON(atomic_read(&anon_vma->refcount));
+ VM_BUG_ON(refcount_read(&anon_vma->refcount));

/*
* Synchronize against page_lock_anon_vma_read() such that
@@ -421,7 +421,7 @@ static void anon_vma_ctor(void *data)
struct anon_vma *anon_vma = data;

init_rwsem(&anon_vma->rwsem);
- atomic_set(&anon_vma->refcount, 0);
+ refcount_set(&anon_vma->refcount, 0);
anon_vma->rb_root = RB_ROOT;
}

@@ -470,7 +470,7 @@ struct anon_vma *page_get_anon_vma(struct page *page)
goto out;

anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
- if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+ if (!refcount_inc_not_zero(&anon_vma->refcount)) {
anon_vma = NULL;
goto out;
}
@@ -529,7 +529,7 @@ struct anon_vma *page_lock_anon_vma_read(struct page *page)
}

/* trylock failed, we got to sleep */
- if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+ if (!refcount_inc_not_zero(&anon_vma->refcount)) {
anon_vma = NULL;
goto out;
}
@@ -544,7 +544,7 @@ struct anon_vma *page_lock_anon_vma_read(struct page *page)
rcu_read_unlock();
anon_vma_lock_read(anon_vma);

- if (atomic_dec_and_test(&anon_vma->refcount)) {
+ if (refcount_dec_and_test(&anon_vma->refcount)) {
/*
* Oops, we held the last refcount, release the lock
* and bail -- can't simply use put_anon_vma() because
@@ -1577,7 +1577,7 @@ void __put_anon_vma(struct anon_vma *anon_vma)
struct anon_vma *root = anon_vma->root;

anon_vma_free(anon_vma);
- if (root != anon_vma && atomic_dec_and_test(&root->refcount))
+ if (root != anon_vma && refcount_dec_and_test(&root->refcount))
anon_vma_free(root);
}

--
2.7.4