Re: [PATCH] rbd: remove VLA usage

[Gustavo A. R. Silva]

On 03/30/2018 03:29 PM, Ilya Dryomov wrote:
> On Fri, Mar 30, 2018 at 9:17 PM, Gustavo A. R. Silva
> <gustavo@xxxxxxxxxxxxxx> wrote:
> > In preparation to enabling -Wvla, remove the use of stack VLA.
> >
> > In this particular case, variable buf_size is replaced with a constant
> > expression that can be computed at preprocessing time. This avoids two
> > VLA warnings. Also, as a consequence of the mentioned change, some code
> > was slightly refactored.
> >
> > The use of stack Variable Length Arrays needs to be avoided, as they
> > can be a vector for stack exhaustion, which can be both a runtime bug
> > or a security flaw. Also, in general, as code evolves it is easy to
> > lose track of how big a VLA can get. Thus, we can end up having runtime
> > failures that are hard to debug.
> >
> > Also, fixed as part of the directive to remove all VLAs from
> > the kernel: https://lkml.org/lkml/2018/3/7/621
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > ---
> >   drivers/block/rbd.c | 15 +++++++--------
> >   1 file changed, 7 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> > index 1e03b04..5133122 100644
> > --- a/drivers/block/rbd.c
> > +++ b/drivers/block/rbd.c
> > @@ -3091,20 +3091,20 @@ static int __rbd_notify_op_lock(struct rbd_device *rbd_dev,
> >   {
> >          struct ceph_osd_client *osdc = &rbd_dev->rbd_client->client->osdc;
> >          struct rbd_client_id cid = rbd_get_cid(rbd_dev);
> > -       int buf_size = 4 + 8 + 8 + CEPH_ENCODING_START_BLK_LEN;
> > -       char buf[buf_size];
> > +       char buf[4 + 8 + 8 + CEPH_ENCODING_START_BLK_LEN];
> >          void *p = buf;
> >
> >          dout("%s rbd_dev %p notify_op %d\n", __func__, rbd_dev, notify_op);
> >
> >          /* encode *LockPayload NotifyMessage (op + ClientId) */
> > -       ceph_start_encoding(&p, 2, 1, buf_size - CEPH_ENCODING_START_BLK_LEN);
> > +       ceph_start_encoding(&p, 2, 1,
> > +                           sizeof(buf) - CEPH_ENCODING_START_BLK_LEN);
> >          ceph_encode_32(&p, notify_op);
> >          ceph_encode_64(&p, cid.gid);
> >          ceph_encode_64(&p, cid.handle);
> >
> >          return ceph_osdc_notify(osdc, &rbd_dev->header_oid,
> > -                               &rbd_dev->header_oloc, buf, buf_size,
> > +                               &rbd_dev->header_oloc, buf, sizeof(buf),
> >                                  RBD_NOTIFY_TIMEOUT, preply_pages, preply_len);
> >   }
> >
> > @@ -3610,19 +3610,18 @@ static void __rbd_acknowledge_notify(struct rbd_device *rbd_dev,
> >                                       u64 notify_id, u64 cookie, s32 *result)
> >   {
> >          struct ceph_osd_client *osdc = &rbd_dev->rbd_client->client->osdc;
> > -       int buf_size = 4 + CEPH_ENCODING_START_BLK_LEN;
> > -       char buf[buf_size];
> > +       char buf[4 + CEPH_ENCODING_START_BLK_LEN];
> > +       int buf_size = 0;
> >          int ret;
> >
> >          if (result) {
> >                  void *p = buf;
> >
> > +               buf_size = sizeof(buf);
> >                  /* encode ResponseMessage */
> >                  ceph_start_encoding(&p, 1, 1,
> >                                      buf_size - CEPH_ENCODING_START_BLK_LEN);
> >                  ceph_encode_32(&p, *result);
> > -       } else {
> > -               buf_size = 0;
> >          }
> >
> >          ret = ceph_osdc_notify_ack(osdc, &rbd_dev->header_oid,
>
> Already fixed:
>
>    https://github.com/ceph/ceph-client/commit/2474e77e75215a3cad3b652d2f55ba5b123cb119

Oh, that's great.

Good to know. :)

Thanks
--
Gustavo