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SubjectRe: KASAN: null-ptr-deref Write in binder_update_page_range
Thanks Minchan!

On Thu, Aug 23, 2018 at 7:29 AM, Minchan Kim <minchan@kernel.org> wrote:
> Signed-off-by: Todd Kjos <tkjos@google.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Martijn Coenen <maco@android.com>

> ---
> drivers/android/binder_alloc.c | 43 +++++++++++++++++++++++++++-------
> 1 file changed, 35 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 3f3b7b253445..64fd96eada31 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -332,6 +332,35 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
> return vma ? -ENOMEM : -ESRCH;
> }
>
> +
> +static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
> + struct vm_area_struct *vma)
> +{
> + if (vma)
> + alloc->vma_vm_mm = vma->vm_mm;
> + /*
> + * If we see alloc->vma is not NULL, buffer data structures set up
> + * completely. Look at smp_rmb side binder_alloc_get_vma.
> + * We also want to guarantee new alloc->vma_vm_mm is always visible
> + * if alloc->vma is set.
> + */
> + smp_wmb();
> + alloc->vma = vma;
> +}
> +
> +static inline struct vm_area_struct *binder_alloc_get_vma(
> + struct binder_alloc *alloc)
> +{
> + struct vm_area_struct *vma = NULL;
> +
> + if (alloc->vma) {
> + /* Look at description in binder_alloc_set_vma */
> + smp_rmb();
> + vma = alloc->vma;
> + }
> + return vma;
> +}
> +
> static struct binder_buffer *binder_alloc_new_buf_locked(
> struct binder_alloc *alloc,
> size_t data_size,
> @@ -348,7 +377,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
> size_t size, data_offsets_size;
> int ret;
>
> - if (alloc->vma == NULL) {
> + if (!binder_alloc_get_vma(alloc)) {
> binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
> "%d: binder_alloc_buf, no vma\n",
> alloc->pid);
> @@ -723,9 +752,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
> buffer->free = 1;
> binder_insert_free_buffer(alloc, buffer);
> alloc->free_async_space = alloc->buffer_size / 2;
> - barrier();
> - alloc->vma = vma;
> - alloc->vma_vm_mm = vma->vm_mm;
> + binder_alloc_set_vma(alloc, vma);
> mmgrab(alloc->vma_vm_mm);
>
> return 0;
> @@ -754,10 +781,10 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
> int buffers, page_count;
> struct binder_buffer *buffer;
>
> - BUG_ON(alloc->vma);
> -
> buffers = 0;
> mutex_lock(&alloc->mutex);
> + BUG_ON(alloc->vma);
> +
> while ((n = rb_first(&alloc->allocated_buffers))) {
> buffer = rb_entry(n, struct binder_buffer, rb_node);
>
> @@ -900,7 +927,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
> */
> void binder_alloc_vma_close(struct binder_alloc *alloc)
> {
> - WRITE_ONCE(alloc->vma, NULL);
> + binder_alloc_set_vma(alloc, NULL);
> }
>
> /**
> @@ -935,7 +962,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
>
> index = page - alloc->pages;
> page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
> - vma = alloc->vma;
> + vma = binder_alloc_get_vma(alloc);
> if (vma) {
> if (!mmget_not_zero(alloc->vma_vm_mm))
> goto err_mmget;
> --
> 2.18.0.1017.ga543ac7ca45-goog
>
>
>
>

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