linux-kernel - [PATCH] clk: mediatek: mt7629: Fix a NULL pointer dereference in mtk_topckgen

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Date:   Wed,  1 Dec 2021 02:15:07 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Wenzhen Yu <wenzhen.yu@...iatek.com>,
        Rob Herring <robh@...nel.org>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] clk: mediatek: mt7629: Fix a NULL pointer dereference in mtk_topckgen_init()

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_MT7629=y show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 3b5e748615e7 ("clk: mediatek: add clock support for MT7629 SoC")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
---
 drivers/clk/mediatek/clk-mt7629.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt7629.c b/drivers/clk/mediatek/clk-mt7629.c
index 856929f94ebd..f791e53b812a 100644
--- a/drivers/clk/mediatek/clk-mt7629.c
+++ b/drivers/clk/mediatek/clk-mt7629.c
@@ -580,6 +580,8 @@ 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