Hi, Elean
Do the issue had really occured, use-after-free. but why the patch
is not received. or is is possible for the situation.
Thanks
zhongjiang
On 2017/2/20 18:49, Elena Reshetova wrote:
> 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);
> }
>
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