On Tue, Aug 09, 2022 at 04:06:31PM +0000, Liam Howlett wrote:
> Take the mmap_read_lock() when using the VMA in
> binder_alloc_print_pages() and when checking for a VMA in
> binder_alloc_new_buf_locked().
>
> It is worth noting binder_alloc_new_buf_locked() drops the VMA read lock
> after it verifies a VMA exists, but may be taken again deeper in the
> call stack, if necessary.
>
> Reported-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> Reported-by: syzbot+a7b60a176ec13cafb793@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: a43cfc87caaf (android: binder: stop saving a pointer to the VMA)
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> drivers/android/binder_alloc.c | 29 +++++++++++++++++++----------
> 1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index f555eebceef6..c23cad7fe313 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -395,12 +395,15 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
> size_t size, data_offsets_size;
> int ret;
>
> + mmap_read_lock(alloc->vma_vm_mm);
> if (!binder_alloc_get_vma(alloc)) {
> + mmap_read_unlock(alloc->vma_vm_mm);
> binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
> "%d: binder_alloc_buf, no vma\n",
> alloc->pid);
> return ERR_PTR(-ESRCH);
> }
> + mmap_read_unlock(alloc->vma_vm_mm);
>
> data_offsets_size = ALIGN(data_size, sizeof(void *)) +
> ALIGN(offsets_size, sizeof(void *));
> @@ -922,17 +925,23 @@ void binder_alloc_print_pages(struct seq_file *m,
> * Make sure the binder_alloc is fully initialized, otherwise we might
> * read inconsistent state.
> */
> - if (binder_alloc_get_vma(alloc) != NULL) {
> - for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) {
> - page = &alloc->pages[i];
> - if (!page->page_ptr)
> - free++;
> - else if (list_empty(&page->lru))
> - active++;
> - else
> - lru++;
> - }
> +
> + mmap_read_lock(alloc->vma_vm_mm);
> + if (binder_alloc_get_vma(alloc) == NULL)
> + goto uninitialized;
> +
> + for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) {
do we need to hold on to the lock while we loop through the pages here?
> + page = &alloc->pages[i];
> + if (!page->page_ptr)
> + free++;
> + else if (list_empty(&page->lru))
> + active++;
> + else
> + lru++;
> }
> +
> +uninitialized:
> + mmap_read_unlock(alloc->vma_vm_mm);
> mutex_unlock(&alloc->mutex);
> seq_printf(m, " pages: %d:%d:%d\n", active, lru, free);
> seq_printf(m, " pages high watermark: %zu\n", alloc->pages_high);
> --
> 2.35.1
