linux-kernel - [PATCH] clk: mediatek: mt8167: Fix a NULL pointer dereference in mtk_apmixedsys

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Date:   Tue, 30 Nov 2021 17:57:50 +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>,
        Fabien Parent <fparent@...libre.com>,
        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: mt8167: Fix a NULL pointer dereference in mtk_apmixedsys_init()

In mtk_apmixedsys_init(), 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_MT8167=y show no new warnings, and our
static analyzer no longer warns about this code.

Fixes: a68224832118 ("clk: mediatek: Add MT8167 clock support")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
---
 drivers/clk/mediatek/clk-mt8167.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/mediatek/clk-mt8167.c b/drivers/clk/mediatek/clk-mt8167.c
index e5ea10e31799..7b18b751487f 100644
--- a/drivers/clk/mediatek/clk-mt8167.c
+++ b/drivers/clk/mediatek/clk-mt8167.c
@@ -1047,6 +1047,11 @@ static void __init mtk_apmixedsys_init(struct device_node *node)
 	}

 	clk_data = mtk_alloc_clk_data(MT8167_CLK_APMIXED_NR_CLK);
+	if (!clk_data) {
+		pr_err("%s(): could not register clock provider: %d\n",
+			__func__, -ENOMEM);
+		return;
+	}

 	mtk_clk_register_plls(node, plls, ARRAY_SIZE(plls), clk_data);
 	mtk_clk_register_dividers(apmixed_adj_divs, ARRAY_SIZE(apmixed_adj_divs),
-- 
2.25.1