[PATCH] i2c: mux: harden i2c_mux_alloc() against integer overflows

[Dan Carpenter <dan.carpenter@oracle.com>]

A couple years back we went through the kernel an automatically
converted size calculations to use struct_size() instead.  The
struct_size() calculation is protected against integer overflows.

However it does not make sense to use the result from struct_size()
for additional math operations as that would negate any safeness.

Fixes: 1f3b69b6b939 ("i2c: mux: Use struct_size() in devm_kzalloc()")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 drivers/i2c/i2c-mux.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 774507b54b57..313904be5f3b 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -243,9 +243,10 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
 				   int (*deselect)(struct i2c_mux_core *, u32))
 {
 	struct i2c_mux_core *muxc;
+	size_t mux_size;
 
-	muxc = devm_kzalloc(dev, struct_size(muxc, adapter, max_adapters)
-			    + sizeof_priv, GFP_KERNEL);
+	mux_size = struct_size(muxc, adapter, max_adapters);
+	muxc = devm_kzalloc(dev, size_add(mux_size, sizeof_priv), GFP_KERNEL);
 	if (!muxc)
 		return NULL;
 	if (sizeof_priv)
-- 
2.35.1