Re: [PATCH] drbd:fix null pointer deref in _drbd_md_sync_page_io

[Lars Ellenberg]

On Wed, Apr 26, 2017 at 02:49:37AM -0700, Heloise wrote:
> The return value of bio_alloc_drbd can be NULL and is used without

No, apparently it cannot, because it is basically a mempool_alloc()
with GFP_NOIO, it may sleep, but it will loop "forever" and not return NULL.

So rather fix that nonsense in bio_alloc_drbd, see below:

Thanks,

    Lars

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 92c60cb..9ffd940 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -150,15 +150,10 @@ static const struct block_device_operations drbd_ops = {
 
 struct bio *bio_alloc_drbd(gfp_t gfp_mask)
 {
-       struct bio *bio;
-
        if (!drbd_md_io_bio_set)
                return bio_alloc(gfp_mask, 1);
 
-       bio = bio_alloc_bioset(gfp_mask, 1, drbd_md_io_bio_set);
-       if (!bio)
-               return NULL;
-       return bio;
+       return bio_alloc_bioset(gfp_mask, 1, drbd_md_io_bio_set);
 }
 
 #ifdef __CHECKER__


> validation, which may cause null-pointer dereference, fix it.
> 
> Signed-off-by: Heloise <o...@iscas.ac.cn>
> ---
>  drivers/block/drbd/drbd_actlog.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/block/drbd/drbd_actlog.c 
> b/drivers/block/drbd/drbd_actlog.c
> index 8d7bcfa..d6bb30e 100644
> --- a/drivers/block/drbd/drbd_actlog.c
> +++ b/drivers/block/drbd/drbd_actlog.c
> @@ -151,6 +151,10 @@ static int _drbd_md_sync_page_io(struct drbd_device 
> *device,
>       op_flags |= REQ_SYNC;
>  
>       bio = bio_alloc_drbd(GFP_NOIO);
> +     if (!bio) {
> +             err = -ENOMEM;
> +             return err;
> +     }
>       bio->bi_bdev = bdev->md_bdev;
>       bio->bi_iter.bi_sector = sector;
>       err = -EIO;
> -- 
> 2.1.0