linux-kernel - Re: [PATCH RFC 3/5] kdbus: do explicit overflow check in kdbus_conn_quota

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Date:	Thu, 2 Jul 2015 10:35:30 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Sergei Zviagintsev <sergei@...v.net>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...glemail.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 3/5] kdbus: do explicit overflow check in kdbus_conn_quota_inc()

Hi

On Sun, Jun 28, 2015 at 3:17 PM, Sergei Zviagintsev <sergei@...v.net> wrote:
> Replace the use of max() with explicit and obvious overflow check.
>
> Signed-off-by: Sergei Zviagintsev <sergei@...v.net>
> ---
>  ipc/kdbus/connection.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/ipc/kdbus/connection.c b/ipc/kdbus/connection.c
> index af044f93c14f..1d44e280eff0 100644
> --- a/ipc/kdbus/connection.c
> +++ b/ipc/kdbus/connection.c
> @@ -668,9 +668,11 @@ int kdbus_conn_quota_inc(struct kdbus_conn *c, struct kdbus_user *u,
>
>         id = u ? u->id : KDBUS_USER_KERNEL_ID;
>         if (id >= c->n_quota) {
> -               unsigned int users;
> +               unsigned int users = KDBUS_ALIGN8(id) + 8;
> +
> +               if (users < id) /* overflow */
> +                       users = id;
>
> -               users = max(KDBUS_ALIGN8(id) + 8, id);

To me, the max() looks fine. I mean, it should be obvious that it
checks for an overflow, right? Otherwise, I'd prefer adding a comment
instead of the explicit conditional.

Thanks
David

>                 quota = krealloc(c->quota, users * sizeof(*quota),
>                                  GFP_KERNEL | __GFP_ZERO);
>                 if (!quota)
> --
> 1.8.3.1
>
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