[PATCH] clk: mediatek: mt8135: Fix a NULL pointer dereference in mtk_topckgen_init()

[Zhou Qingyang]

In mtk_topckgen_init(), mtk_alloc_clk_data() is assigned to clk_data
and used in clk_prepare_enable(). There is dereference of clk_data
in clk_prepare_enable(), which could lead to a NULL pointer dereference
on failure of mtk_alloc_clk_data().

Fix this bug by adding a check of clk_data.

Another way to fix this bug is to add a check of clk_data in
clk_prepare_enable(), which may solve many similar bugs but could
cause potential problems to previously correct cases as the API is
changed.

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_MT8135=y show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: a8aede794843 ("clk: mediatek: Add basic clocks for Mediatek MT8135.")
Signed-off-by: Zhou Qingyang <zhou1615@xxxxxxx>
---
 drivers/clk/mediatek/clk-mt8135.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt8135.c b/drivers/clk/mediatek/clk-mt8135.c
index b4e20bd7680e..556153379c3d 100644
--- a/drivers/clk/mediatek/clk-mt8135.c
+++ b/drivers/clk/mediatek/clk-mt8135.c
@@ -526,6 +526,11 @@ static void __init mtk_topckgen_init(struct device_node *node)
 	}
 
 	clk_data = mtk_alloc_clk_data(CLK_TOP_NR_CLK);
+	if (!clk_data) {
+		pr_err("%s(): could not register clock provider: %d\n",
+			__func__, -ENOMEM);
+		return;
+	}
 
 	mtk_clk_register_factors(root_clk_alias, ARRAY_SIZE(root_clk_alias), clk_data);
 	mtk_clk_register_factors(top_divs, ARRAY_SIZE(top_divs), clk_data);
-- 
2.25.1