2019-02-08 00:56:33

by Gustavo A. R. Silva

Subject: [PATCH net-next] netfilter: xt_recent: Use struct_size() in kvzalloc()

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;
void *entry[];
};

size = sizeof(struct foo) + count * sizeof(void *);
instance = alloc(size, GFP_KERNEL)

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

size = struct_size(instance, entry, count);
instance = alloc(size, GFP_KERNEL)

Notice that, in this case, variable sz is not necessary, hence it is
removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
net/netfilter/xt_recent.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c
index f44de4bc2100..1664d2ec8b2f 100644
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -337,7 +337,6 @@ static int recent_mt_check(const struct xt_mtchk_param *par,
unsigned int nstamp_mask;
unsigned int i;
int ret = -EINVAL;
- size_t sz;

net_get_random_once(&hash_rnd, sizeof(hash_rnd));

@@ -387,8 +386,7 @@ static int recent_mt_check(const struct xt_mtchk_param *par,
goto out;
}

- sz = sizeof(*t) + sizeof(t->iphash[0]) * ip_list_hash_size;
- t = kvzalloc(sz, GFP_KERNEL);
+ t = kvzalloc(struct_size(t, iphash, ip_list_hash_size), GFP_KERNEL);
if (t == NULL) {
ret = -ENOMEM;
goto out;
--
2.20.1

2019-02-11 23:45:49

by Pablo Neira Ayuso

Subject: Re: [PATCH net-next] netfilter: xt_recent: Use struct_size() in kvzalloc()

On Thu, Feb 07, 2019 at 06:56:08PM -0600, Gustavo A. R. Silva 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;
> void *entry[];
> };
>
> size = sizeof(struct foo) + count * sizeof(void *);
> instance = alloc(size, GFP_KERNEL)
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> size = struct_size(instance, entry, count);
> instance = alloc(size, GFP_KERNEL)
>
> Notice that, in this case, variable sz is not necessary, hence it is
> removed.
>
> This code was detected with the help of Coccinelle.

Applied, thanks.