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

[Christophe Leroy]

Le 26/11/2021 à 17:00, Greg Kroah-Hartman a écrit :
On Fri, Nov 19, 2021 at 10:15:09AM +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>
---
  drivers/w1/slaves/w1_ds28e04.c | 10 ++--------
  1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/w1/slaves/w1_ds28e04.c b/drivers/w1/slaves/w1_ds28e04.c
index e4f336111edc..d75bb16fb7a1 100644
--- a/drivers/w1/slaves/w1_ds28e04.c
+++ b/drivers/w1/slaves/w1_ds28e04.c
@@ -339,10 +339,7 @@ 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 sprintf(buf, "%d", w1_enable_crccheck);

This should be sysfs_emit(), right?

Ok


  }
  
  static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
@@ -353,11 +350,8 @@ static ssize_t crccheck_store(struct device *dev, struct 
device_attribute *attr,
        if (count != 1 || !buf)
                return -EINVAL;
  
-	if (get_user(val, buf))
-               return -EFAULT;
-
        /* convert to decimal */
-       val = val - 0x30;
+       val = *buf - 0x30;

Why not use a proper function that can parse a string and turn it into a
number?

I wanted to keep the change minimal. But I can also replace it with some 
scanf.

But don't we have any generic function to read and store a bool after all ?

Thanks
Christophe