clk: clk-loongson2: Fix potential buffer overflow in flexible-array member access

Flexible-array member hws in struct clk_hw_onecell_data is annotated with the counted_by() attribute. This means that when memory is allocated for this array, the _counter_, which in this case is member num in the flexible structure, should be set to the maximum number of elements the flexible array can contain, or fewer.

In this case, the total number of elements for the flexible array is determined by variable clks_num when allocating heap space via devm_kzalloc(), as shown below:

289         struct loongson2_clk_provider *clp;
	...

296 for (p = data; p->name; p++)
297 clks_num++;
298
299 clp = devm_kzalloc(dev, struct_size(clp, clk_data.hws, clks_num),
300 GFP_KERNEL);

So, clp->clk_data.num should be set to clks_num or less, and not exceed clks_num, as is currently the case. Otherwise, if data is written into clp->clk_data.hws[clks_num], the instrumentation provided by the compiler won't detect the overflow, leading to a memory corruption bug at runtime.

Fix this issue by setting clp->clk_data.num to clks_num.

---
 drivers/clk/clk-loongson2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e99ba79feec6..7082b4309c6f 100644
@@ -306,7 +306,7 @@ static int loongson2_clk_probe(struct platform_device *pdev)
 		return PTR_ERR(clp->base);
 
 	spin_lock_init(&clp->clk_lock);
-	clp->clk_data.num = clks_num + 1;
+	clp->clk_data.num = clks_num;
 	clp->dev = dev;
 
 	for (i = 0; i < clks_num; i++) {

2.43.0

Quoting Gustavo A. R. Silva (2024-11-14 15:55:16)

Applied to clk-next