[PATCH] clk: mediatek: mt7622: 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.

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_MT7622=y show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 2fc0a509e4ee ("clk: mediatek: add clock support for MT7622 SoC")
Signed-off-by: Zhou Qingyang <zhou1615 at umn.edu>
---
 drivers/clk/mediatek/clk-mt7622.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt7622.c b/drivers/clk/mediatek/clk-mt7622.c
index e89acef5768f..4968b227b4ab 100644
--- a/drivers/clk/mediatek/clk-mt7622.c
+++ b/drivers/clk/mediatek/clk-mt7622.c
@@ -620,6 +620,8 @@ static int mtk_topckgen_init(struct platform_device *pdev)
 		return PTR_ERR(base);
 
 	clk_data = mtk_alloc_clk_data(CLK_TOP_NR_CLK);
+	if (!clk_data)
+		return -ENOMEM;
 
 	mtk_clk_register_fixed_clks(top_fixed_clks, ARRAY_SIZE(top_fixed_clks),
 				    clk_data);
-- 
2.25.1