linux-kernel - [PATCH v3] w1: Misuse of get_user()/put

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Message-Id: <d14ed8d71ad4372e6839ae427f91441d3ba0e94d.1637946316.git.christophe.leroy@csgroup.eu>
Date:   Fri, 26 Nov 2021 18:06:46 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Evgeniy Polyakov <zbr@...emap.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kernel test robot <lkp@...el.com>
Subject: [PATCH v3] w1: Misuse of get_user()/put_user() reported by sparse

sparse warnings: (new ones prefixed by >>)
>> drivers/w1/slaves/w1_ds28e04.c:342:13: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected char [noderef] __user *_pu_addr @@     got char *buf @@
   drivers/w1/slaves/w1_ds28e04.c:342:13: sparse:     expected char [noderef] __user *_pu_addr
   drivers/w1/slaves/w1_ds28e04.c:342:13: sparse:     got char *buf
>> drivers/w1/slaves/w1_ds28e04.c:356:13: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected char const [noderef] __user *_gu_addr @@     got char const *buf @@
   drivers/w1/slaves/w1_ds28e04.c:356:13: sparse:     expected char const [noderef] __user *_gu_addr
   drivers/w1/slaves/w1_ds28e04.c:356:13: sparse:     got char const *buf

The buffer buf is a failsafe buffer in kernel space, it's not user
memory hence doesn't deserve the use of get_user() or put_user().

Access 'buf' content directly.

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/202111190526.K5vb7NWC-lkp@intel.com/T/
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
v3: Rewrite crccheck_store() more userfriendly

v2: Use sysfs_emit() and kstrtobool()
---
 drivers/w1/slaves/w1_ds28e04.c | 26 ++++++--------------------
 1 file changed, 6 insertions(+), 20 deletions(-)

diff --git a/drivers/w1/slaves/w1_ds28e04.c b/drivers/w1/slaves/w1_ds28e04.c
index e4f336111edc..6cef6e2edb89 100644
--- a/drivers/w1/slaves/w1_ds28e04.c
+++ b/drivers/w1/slaves/w1_ds28e04.c
@@ -32,7 +32,7 @@ static int w1_strong_pullup = 1;
 module_param_named(strong_pullup, w1_strong_pullup, int, 0);
 
 /* enable/disable CRC checking on DS28E04-100 memory accesses */
-static char w1_enable_crccheck = 1;
+static bool w1_enable_crccheck = true;
 
 #define W1_EEPROM_SIZE		512
 #define W1_PAGE_COUNT		16
@@ -339,32 +339,18 @@ static BIN_ATTR_RW(pio, 1);
 static ssize_t crccheck_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
-	if (put_user(w1_enable_crccheck + 0x30, buf))
-		return -EFAULT;
-
-	return sizeof(w1_enable_crccheck);
+	return sysfs_emit(buf, "%d\n", w1_enable_crccheck);
 }
 
 static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
-	char val;
-
-	if (count != 1 || !buf)
-		return -EINVAL;
+	int err = kstrtobool(buf, &w1_enable_crccheck);
 
-	if (get_user(val, buf))
-		return -EFAULT;
+	if (err)
+		return err;
 
-	/* convert to decimal */
-	val = val - 0x30;
-	if (val != 0 && val != 1)
-		return -EINVAL;
-
-	/* set the new value */
-	w1_enable_crccheck = val;
-
-	return sizeof(w1_enable_crccheck);
+	return count;
 }
 
 static DEVICE_ATTR_RW(crccheck);
-- 
2.33.1