[PATCH] hwmon: (lm90) Fix error return value from detect function

[Guenter Roeck <linux@roeck-us.net>]

lm90_detect_nuvoton() is supposed to return NULL if it can not detect
a chip, or a pointer to the chip name if it does. Under some circumstances
it returns an error pointer instead. Some versions of gcc interpret an
ERR_PTR as region of size 0 and generate an error message.

  In function ‘__fortify_strlen’,
      inlined from ‘strlcpy’ at ./include/linux/fortify-string.h:159:10,
      inlined from ‘lm90_detect’ at drivers/hwmon/lm90.c:2550:2:
  ./include/linux/fortify-string.h:50:33: error:
      ‘__builtin_strlen’ reading 1 or more bytes from a region of size 0
     50 | #define __underlying_strlen     __builtin_strlen
        |                                 ^
  ./include/linux/fortify-string.h:141:24: note:
      in expansion of macro ‘__underlying_strlen’
    141 |                 return __underlying_strlen(p);
        |                        ^~~~~~~~~~~~~~~~~~~

Returning NULL instead of ERR_PTR() fixes the problem.

Fixes: c7cebce984a2 ("hwmon: (lm90) Rework detect function")
Reported-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
It is interesting that some versions of gcc interpret an ERR_PTR this way.
It did find a real bug, though the error message is quite confusing.
Would it be possible to enhance the fortify functions to detect a constant
ERR_PTR at compile time ? I think that might be quite useful.

 drivers/hwmon/lm90.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
index 03d07da8c2dc..221de01a327a 100644
--- a/drivers/hwmon/lm90.c
+++ b/drivers/hwmon/lm90.c
@@ -2321,7 +2321,7 @@ static const char *lm90_detect_nuvoton(struct i2c_client *client, int chip_id,
 	const char *name = NULL;
 
 	if (config2 < 0)
-		return ERR_PTR(-ENODEV);
+		return NULL;
 
 	if (address == 0x4c && !(config1 & 0x2a) && !(config2 & 0xf8)) {
 		if (chip_id == 0x01 && convrate <= 0x09) {
-- 
2.36.2