[next] ceph: Replace zero-length array with flexible array member

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

Notice that, in this case, sizeof(au->reply_buf) translates to zero,
becase in the original code reply_buf is a zero-length array. Now that
reply_buf is transformed into a flexible array, the mentioned line of
code is now replaced by a literal 0.

Also, as a safeguard, explicitly assign NULL to
auth->authorizer_reply_buf, as no heap is allocated for it, therefore
it should not be accessible.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 net/ceph/auth_none.c | 4 ++--
 net/ceph/auth_none.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

On Fri, May 14, 2021 at 11:51 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
>

> There is a regular need in the kernel to provide a way to declare

> having a dynamically sized set of trailing elements in a structure.

> Kernel code should always use “flexible array members”[1] for these

> cases. The older style of one-element or zero-length arrays should

> no longer be used[2].

>

> Notice that, in this case, sizeof(au->reply_buf) translates to zero,

> becase in the original code reply_buf is a zero-length array. Now that

> reply_buf is transformed into a flexible array, the mentioned line of

> code is now replaced by a literal 0.

>

> Also, as a safeguard, explicitly assign NULL to

> auth->authorizer_reply_buf, as no heap is allocated for it, therefore

> it should not be accessible.

>

> [1] https://en.wikipedia.org/wiki/Flexible_array_member

> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

>

> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

> ---

>  net/ceph/auth_none.c | 4 ++--

>  net/ceph/auth_none.h | 2 +-

>  2 files changed, 3 insertions(+), 3 deletions(-)

>

> diff --git a/net/ceph/auth_none.c b/net/ceph/auth_none.c

> index 70e86e462250..10ee16d2cbf0 100644

> --- a/net/ceph/auth_none.c

> +++ b/net/ceph/auth_none.c

> @@ -111,8 +111,8 @@ static int ceph_auth_none_create_authorizer(

>         auth->authorizer = (struct ceph_authorizer *) au;

>         auth->authorizer_buf = au->buf;

>         auth->authorizer_buf_len = au->buf_len;

> -       auth->authorizer_reply_buf = au->reply_buf;

> -       auth->authorizer_reply_buf_len = sizeof (au->reply_buf);

> +       auth->authorizer_reply_buf_len = 0;

> +       auth->authorizer_reply_buf = NULL;

>

>         return 0;

>  }

> diff --git a/net/ceph/auth_none.h b/net/ceph/auth_none.h

> index 4158f064302e..3c68c0ee3dab 100644

> --- a/net/ceph/auth_none.h

> +++ b/net/ceph/auth_none.h

> @@ -16,7 +16,7 @@ struct ceph_none_authorizer {

>         struct ceph_authorizer base;

>         char buf[128];

>         int buf_len;

> -       char reply_buf[0];

> +       char reply_buf[];

>  };

>

>  struct ceph_auth_none_info {


Hi Gustavo,

I went ahead and removed reply_buf.  We never receive authorizer
replies in auth_none mode, so patching it to be a flexible array
is rather pointless.

Thanks,

                Ilya

On 5/15/21 05:42, Ilya Dryomov wrote:
> 
> Hi Gustavo,
> 
> I went ahead and removed reply_buf.  We never receive authorizer
> replies in auth_none mode, so patching it to be a flexible array
> is rather pointless.

Sounds great. :)

Thanks, Ilya.
--
Gustavo