[PATCH] clk: mediatek: mt2712: Fix a NULL pointer dereference in clk_mt2712_top_init_early()

[Zhou Qingyang]

In clk_mt2712_top_init_early(), mtk_alloc_clk_data() is assigned to
top_clk_data and there is a dereference of it in
clk_mt2712_top_init_early() which could lead to a NULL pointer
dereference on failure of mtk_alloc_clk_data().

Fix this bug by adding a check of top_clk_data.

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_COMMON_CLK_MT2712=y show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: e2f744a82d72 ("clk: mediatek: Add MT2712 clock support")
Signed-off-by: Zhou Qingyang <zhou1615 at umn.edu>
---
 drivers/clk/mediatek/clk-mt2712.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt2712.c b/drivers/clk/mediatek/clk-mt2712.c
index 08ef56f68c7a..9050927d2d5d 100644
--- a/drivers/clk/mediatek/clk-mt2712.c
+++ b/drivers/clk/mediatek/clk-mt2712.c
@@ -1286,6 +1286,11 @@ static void clk_mt2712_top_init_early(struct device_node *node)
 
 	if (!top_clk_data) {
 		top_clk_data = mtk_alloc_clk_data(CLK_TOP_NR_CLK);
+		if (!top_clk_data) {
+			pr_err("%s(): could not register clock provider: %d\n",
+				__func__, -ENOMEM);
+			return;
+		}
 
 		for (i = 0; i < CLK_TOP_NR_CLK; i++)
 			top_clk_data->clks[i] = ERR_PTR(-EPROBE_DEFER);
-- 
2.25.1