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From:   Ilya Dryomov <idryomov@gmail.com>
Date:   Thu, 17 Jan 2019 15:17:33 +0100
Message-ID: <CAOi1vP_yWH2mhquFObC6VnUzNTzc7PX7tqA3RP=ci71BMm-gqA@mail.gmail.com>
Subject: Re: [PATCH net-next] libceph, ceph: use struct_size() in kmalloc()
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc:     "Yan, Zheng" <zyan@redhat.com>, Sage Weil <sage@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Ceph Development <ceph-devel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, linux-kernel@vger.kernel.org
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On Tue, Jan 15, 2019 at 8:41 PM Gustavo A. R. Silva
<gustavo@embeddedor.com> wrote:
>
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
>
> struct foo {
>     int stuff;
>     struct boo entry[];
> };
>
> instance = kmalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP_KERNEL);
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>
> This code was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  net/ceph/osdmap.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
> index 98c0ff3d6441..48a31dc9161c 100644
> --- a/net/ceph/osdmap.c
> +++ b/net/ceph/osdmap.c
> @@ -495,9 +495,8 @@ static struct crush_map *crush_decode(void *pbyval, void *end)
>                           / sizeof(struct crush_rule_step))
>                         goto bad;
>  #endif
> -               r = c->rules[i] = kmalloc(sizeof(*r) +
> -                                         yes*sizeof(struct crush_rule_step),
> -                                         GFP_NOFS);
> +               r = kmalloc(struct_size(r, steps, yes), GFP_NOFS);
> +               c->rules[i] = r;
>                 if (r == NULL)
>                         goto badmem;
>                 dout(" rule %d is at %p\n", i, r);

Applied.

Thanks,

                Ilya