linux-kernel - [PATCH net-next] net: dsa: use struct_size() in devm

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Date:   Thu, 7 Feb 2019 19:16:03 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH net-next] net: dsa: use struct_size() in devm_kzalloc()

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[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
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:

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

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

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 net/dsa/dsa2.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index a1917025e155..8c431e0f3627 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -767,11 +767,10 @@ static int dsa_switch_probe(struct dsa_switch *ds)
 
 struct dsa_switch *dsa_switch_alloc(struct device *dev, size_t n)
 {
-	size_t size = sizeof(struct dsa_switch) + n * sizeof(struct dsa_port);
 	struct dsa_switch *ds;
 	int i;
 
-	ds = devm_kzalloc(dev, size, GFP_KERNEL);
+	ds = devm_kzalloc(dev, struct_size(ds, ports, n), GFP_KERNEL);
 	if (!ds)
 		return NULL;
 
-- 
2.20.1