Re: [PATCH v2] w1: Misuse of get_user()/put_user() reported by sparse

Le 26/11/2021 à 17:54, Greg Kroah-Hartman a écrit :

On Fri, Nov 26, 2021 at 05:47:58PM +0100, Christophe Leroy wrote:

quoted

sparse warnings: (new ones prefixed by >>)

quoted

quoted

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

quoted

quoted

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 <redacted>
Link: https://lore.kernel.org/lkml/202111190526.K5vb7NWC-lkp@intel.com/T/ (local)
Signed-off-by: Christophe Leroy <redacted>
---
v2: Use sysfs_emit() and kstrtobool()
---
  drivers/w1/slaves/w1_ds28e04.c | 25 +++----------------------
  1 file changed, 3 insertions(+), 22 deletions(-)

diff --git a/drivers/w1/slaves/w1_ds28e04.c b/drivers/w1/slaves/w1_ds28e04.c
index e4f336111edc..98f80f412cfd 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 +339,13 @@ 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;
-
-	if (get_user(val, buf))
-		return -EFAULT;
-
-	/* 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 kstrtobool(buf, &w1_enable_crccheck) ? : count;

Please spell this line out, using ? : is unreadable at times.

You prefer something like:

	int err = kstrtobool(buf, &w1_enable_crccheck);

	return err ? err : count;


Or

	int err = kstrtobool(buf, &w1_enable_crccheck);

	if (err)
		return err;

	return count;

?