[PATCH] clk: mediatek: mt6779: Fix a NULL pointer dereference in clk_mt6779_top_probe()

[Zhou Qingyang]

In clk_mt6779_top_probe(), mtk_alloc_clk_data() is assigned to clk_data
and used in mtk_clk_register_muxes(). There is dereference of clk_data
in mtk_clk_register_muxes(), 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
mtk_clk_register_muxes(), 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_MT6779=y show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 710774e04861 ("clk: mediatek: Add MT6779 clock support")
Signed-off-by: Zhou Qingyang <zhou1615 at umn.edu>
---
 drivers/clk/mediatek/clk-mt6779.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt6779.c b/drivers/clk/mediatek/clk-mt6779.c
index f22bf4025f55..fb43d23b715b 100644
--- a/drivers/clk/mediatek/clk-mt6779.c
+++ b/drivers/clk/mediatek/clk-mt6779.c
@@ -1239,6 +1239,8 @@ static int clk_mt6779_top_probe(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