linux-kernel - [PATCH v2] clk: x86: Fix a wild pointer dereference in fch_clk

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Date:   Fri,  7 Jan 2022 15:15:58 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Akshu Agrawal <akshu.agrawal@....com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] clk: x86: Fix a wild pointer dereference in fch_clk_probe()

In fch_clk_probe(), the return value of clk_hw_register_mux() is
assigned to hws[ST_CLK_MUX] and there is a dereference of it in
fch_clk_probe(), which could lead to a wild pointer dereference on
failure of clk_hw_register_mux().

Fix this bug by adding a check of hws[ST_CLK_MUX].

This bug was found by a static analyzer.

Builds with CONFIG_X86_AMD_PLATFORM_DEVICE=y show no new warnings, and
our static analyzer no longer warns about this code.

Fixes: 19fe87fd854a ("clk: x86: Support RV architecture")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
--- 
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.

Changes in v2:
  -  Add error check to every register function calls.
  -  Add error handling logic to every error path.
  -  Turn clk_hw_register_mux to devm_clk_hw_register_mux.
  -  Add error check of clk_set_parent().

 drivers/clk/x86/clk-fch.c | 53 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 49 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/x86/clk-fch.c b/drivers/clk/x86/clk-fch.c
index 8f7c5142b0f0..47754761b19c 100644
--- a/drivers/clk/x86/clk-fch.c
+++ b/drivers/clk/x86/clk-fch.c
@@ -36,6 +36,7 @@ static struct clk_hw *hws[ST_MAX_CLKS];
 static int fch_clk_probe(struct platform_device *pdev)
 {
 	struct fch_clk_data *fch_data;
+	int ret;
 
 	fch_data = dev_get_platdata(&pdev->dev);
 	if (!fch_data || !fch_data->base)
@@ -44,35 +45,79 @@ static int fch_clk_probe(struct platform_device *pdev)
 	if (!fch_data->is_rv) {
 		hws[ST_CLK_48M] = clk_hw_register_fixed_rate(NULL, "clk48MHz",
 			NULL, 0, 48000000);
+		if (IS_ERR(hws[ST_CLK_48M]))
+			return PTR_ERR(hws[ST_CLK_48M]);
+
 		hws[ST_CLK_25M] = clk_hw_register_fixed_rate(NULL, "clk25MHz",
 			NULL, 0, 25000000);
+		if (IS_ERR(hws[ST_CLK_25M])) {
+			ret = PTR_ERR(hws[ST_CLK_25M]);
+			goto err_st_clk_25m;
+		}
 
-		hws[ST_CLK_MUX] = clk_hw_register_mux(NULL, "oscout1_mux",
+		hws[ST_CLK_MUX] = devm_clk_hw_register_mux(NULL, "oscout1_mux",
 			clk_oscout1_parents, ARRAY_SIZE(clk_oscout1_parents),
 			0, fch_data->base + CLKDRVSTR2, OSCOUT1CLK25MHZ, 3, 0,
 			NULL);
+		if (IS_ERR(hws[ST_CLK_MUX])) {
+			ret = PTR_ERR(hws[ST_CLK_MUX]);
+			goto err_st_clk_mux;
+		}
 
-		clk_set_parent(hws[ST_CLK_MUX]->clk, hws[ST_CLK_48M]->clk);
+		ret = clk_set_parent(hws[ST_CLK_MUX]->clk, hws[ST_CLK_48M]->clk);
+		if (ret)
+			goto err_clk_set_parent;
 
 		hws[ST_CLK_GATE] = clk_hw_register_gate(NULL, "oscout1",
 			"oscout1_mux", 0, fch_data->base + MISCCLKCNTL1,
 			OSCCLKENB, CLK_GATE_SET_TO_DISABLE, NULL);
+		if (IS_ERR(hws[ST_CLK_GATE])) {
+			ret = PTR_ERR(hws[ST_CLK_GATE]);
+			goto err_st_clk_gate;
+		}
 
-		devm_clk_hw_register_clkdev(&pdev->dev, hws[ST_CLK_GATE],
+		ret = devm_clk_hw_register_clkdev(&pdev->dev, hws[ST_CLK_GATE],
 			"oscout1", NULL);
+		if (ret)
+			goto err_register_st_clk_gate;
 	} else {
 		hws[RV_CLK_48M] = clk_hw_register_fixed_rate(NULL, "clk48MHz",
 			NULL, 0, 48000000);
+		if (IS_ERR(hws[RV_CLK_48M]))
+			return PTR_ERR(hws[RV_CLK_48M]);
 
 		hws[RV_CLK_GATE] = clk_hw_register_gate(NULL, "oscout1",
 			"clk48MHz", 0, fch_data->base + MISCCLKCNTL1,
 			OSCCLKENB, CLK_GATE_SET_TO_DISABLE, NULL);
+		if (IS_ERR(hws[RV_CLK_GATE])) {
+			ret = PTR_ERR(hws[RV_CLK_GATE]);
+			goto err_rv_clk_gate;
+		}
 
-		devm_clk_hw_register_clkdev(&pdev->dev, hws[RV_CLK_GATE],
+		ret = devm_clk_hw_register_clkdev(&pdev->dev, hws[RV_CLK_GATE],
 			"oscout1", NULL);
+		if (ret)
+			goto err_register_rv_clk_gate;
 	}
 
 	return 0;
+
+err_register_st_clk_gate:
+	clk_hw_unregister_gate(hws[ST_CLK_GATE]);
+err_st_clk_gate:
+err_clk_set_parent:
+	clk_hw_unregister_mux(hws[ST_CLK_MUX]);
+err_st_clk_mux:
+	clk_hw_unregister_fixed_rate(hws[ST_CLK_25M]);
+err_st_clk_25m:
+	clk_hw_unregister_fixed_rate(hws[ST_CLK_48M]);
+	return ret;
+
+err_register_rv_clk_gate:
+	clk_hw_unregister_gate(hws[RV_CLK_GATE]);
+err_rv_clk_gate:
+	clk_hw_unregister_fixed_rate(hws[RV_CLK_48M]);
+	return ret;
 }
 
 static int fch_clk_remove(struct platform_device *pdev)
-- 
2.25.1