[PATCH v3] platform/x86: think-lmi: Fix current password length check

[Thorsten Blum]

current_password_store() checks the password length before removing the
trailing newline, which can reject valid passwords that are exactly
->maxlen bytes long.

It also passes ->maxlen to strscpy(), which truncates passwords without
a newline.

Use strchrnul() to measure the password length up to the newline, then
copy that many bytes and add a trailing NUL terminator using strscpy().

Fixes: a40cd7ef22fb ("platform/x86: think-lmi: Add WMI interface support on Lenovo platforms")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Mark Pearson <mpearson-lenovo@xxxxxxxxx>
Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
---
Changes in v3:
- Use strscpy() instead of memcpy() + manual NUL termination (Ilpo)
- v2: https://lore.kernel.org/r/20260813082049.41209-2-thorsten.blum@xxxxxxxxx/

Changes in v2:
- Keep and reword the newline comment
- v1: https://lore.kernel.org/r/20260810132018.156868-3-thorsten.blum@xxxxxxxxx/
---
 drivers/platform/x86/lenovo/think-lmi.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/platform/x86/lenovo/think-lmi.c b/drivers/platform/x86/lenovo/think-lmi.c
index e215e86e3db7..c1ccdd7491af 100644
--- a/drivers/platform/x86/lenovo/think-lmi.c
+++ b/drivers/platform/x86/lenovo/think-lmi.c
@@ -438,14 +438,13 @@ static ssize_t current_password_store(struct kobject *kobj,
 	struct tlmi_pwd_setting *setting = to_tlmi_pwd_setting(kobj);
 	size_t pwdlen;
 
-	pwdlen = strlen(buf);
+	/* Strip newline; setting password won't work if one is present. */
+	pwdlen = strchrnul(buf, '\n') - buf;
 	/* pwdlen == 0 is allowed to clear the password */
 	if (pwdlen && ((pwdlen < setting->minlen) || (pwdlen > setting->maxlen)))
 		return -EINVAL;
 
-	strscpy(setting->password, buf, setting->maxlen);
-	/* Strip out CR if one is present, setting password won't work if it is present */
-	strreplace(setting->password, '\n', '\0');
+	strscpy(setting->password, buf, pwdlen + 1);
 	return count;
 }