linux-kernel - [PATCH] clk: imx: Fix a NULL pointer dereference in imx_register_uart

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Date:   Tue, 25 Jan 2022 00:52:06 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Abel Vesa <abel.vesa@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Adam Ford <aford173@...il.com>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] clk: imx: Fix a NULL pointer dereference in imx_register_uart_clocks()

In imx_register_uart_clocks(), the global variable imx_uart_clocks is
assigned by kcalloc() and there is a dereference of in the next for loop,
which could introduce a NULL pointer dereference on failure of kcalloc().

Fix this by adding a NULL check of imx_uart_clocks.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 379c9a24cc23 ("clk: imx: Fix reparenting of UARTs not associated with stdout")
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.

 drivers/clk/imx/clk.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/clk/imx/clk.c b/drivers/clk/imx/clk.c
index 7cc669934253..99249ab361d2 100644
--- a/drivers/clk/imx/clk.c
+++ b/drivers/clk/imx/clk.c
@@ -173,6 +173,8 @@ void imx_register_uart_clocks(unsigned int clk_count)
 		int i;
 
 		imx_uart_clocks = kcalloc(clk_count, sizeof(struct clk *), GFP_KERNEL);
+		if (!imx_uart_clocks)
+			return;
 
 		if (!of_stdout)
 			return;
-- 
2.25.1