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

[Christophe Leroy]

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:

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 <l...@intel.com>
Link: https://lore.kernel.org/lkml/202111190526.k5vb7nwc-...@intel.com/T/
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
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;

?