[PATCH] clk: mediatek: mt6779: Fix a NULL pointer dereference in clk_mt6779_apmixed_probe()

[Zhou Qingyang]

In clk_mt6779_apmixed_probe(), the return value of
mtk_alloc_clk_data() is assigned to clk_data and used in
mtk_clk_register_plls(). There is a dereference of clk_data in
mtk_clk_register_plls(), 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_plls(), 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 9825385c9f94..f22bf4025f55 100644
--- a/drivers/clk/mediatek/clk-mt6779.c
+++ b/drivers/clk/mediatek/clk-mt6779.c
@@ -1217,6 +1217,8 @@ static int clk_mt6779_apmixed_probe(struct platform_device *pdev)
 	struct device_node *node = pdev->dev.of_node;
 
 	clk_data = mtk_alloc_clk_data(CLK_APMIXED_NR_CLK);
+	if (!clk_data)
+		return -ENOMEM;
 
 	mtk_clk_register_plls(node, plls, ARRAY_SIZE(plls), clk_data);
 
-- 
2.25.1