linux-kernel - [PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos

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Date:   Mon, 11 Jan 2021 14:09:04 -0800
From:   trix@...hat.com
To:     johan@...nel.org, gregkh@...uxfoundation.org,
        natechancellor@...il.com, ndesaulniers@...gle.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, Tom Rix <trix@...hat.com>
Subject: [PATCH] USB: serial: mos7720: improve handling of a kmalloc failure in read_mos_reg()

From: Tom Rix <trix@...hat.com>

clang static analysis reports this problem

mos7720.c:352:2: warning: Undefined or garbage value returned to caller
        return d;
        ^~~~~~~~

In the parport_mos7715_read_data()'s call to read_mos_reg(), 'd' is
only set after the alloc block.

	buf = kmalloc(1, GFP_KERNEL);
	if (!buf)
		return -ENOMEM;

Although the problem is reported in parport_most7715_read_data(),
none of the callee's of read_mos_reg() check the return status.

So move the clearing of data to before the malloc.

Fixes: 0d130367abf5 ("USB: serial: mos7720: fix control-message error handling")
Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/usb/serial/mos7720.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
index 41ee2984a0df..23e8162c768b 100644
--- a/drivers/usb/serial/mos7720.c
+++ b/drivers/usb/serial/mos7720.c
@@ -214,6 +214,7 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
 	u8 *buf;
 	int status;
 
+	*data = 0;
 	buf = kmalloc(1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
@@ -227,7 +228,6 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
 			"mos7720: usb_control_msg() failed: %d\n", status);
 		if (status >= 0)
 			status = -EIO;
-		*data = 0;
 	}
 
 	kfree(buf);
-- 
2.27.0