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

["Mark Pearson" <mpearson-lenovo@squebb.ca>]

On Tue, Aug 11, 2026, at 4:29 PM, Thorsten Blum wrote:
> On Tue, Aug 11, 2026 at 03:29:28PM -0400, Mark Pearson wrote:
>> On Mon, Aug 10, 2026, at 9:20 AM, Thorsten Blum wrote:
>> > 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.
>> >
>> > Fixes: a40cd7ef22fb ("platform/x86: think-lmi: Add WMI interface 
>> > support on Lenovo platforms")
>> > Cc: stable@vger.kernel.org
>> > Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
>> > ---
>> >  drivers/platform/x86/lenovo/think-lmi.c | 8 +++-----
>> >  1 file changed, 3 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/drivers/platform/x86/lenovo/think-lmi.c 
>> > b/drivers/platform/x86/lenovo/think-lmi.c
>> > index e215e86e3db7..860224dc8c21 100644
>> > --- a/drivers/platform/x86/lenovo/think-lmi.c
>> > +++ b/drivers/platform/x86/lenovo/think-lmi.c
>> > @@ -436,16 +436,14 @@ static ssize_t current_password_store(struct 
>> > kobject *kobj,
>> >  				      const char *buf, size_t count)
>> >  {
>> >  	struct tlmi_pwd_setting *setting = to_tlmi_pwd_setting(kobj);
>> > -	size_t pwdlen;
>> > +	size_t pwdlen = strchrnul(buf, '\n') - buf;
>> > 
>> > -	pwdlen = strlen(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');
>> > +	memcpy(setting->password, buf, pwdlen);
>> > +	setting->password[pwdlen] = '\0';
>> >  	return count;
>> >  }
>> 
>> Change is good.
>> Only minor note is that I hate to lose the comment explaining why
>> we're losing the CR. Can we put that back in above the strchrnul
>> operation?
>
> I removed the comment because '\r' is CR and '\n' is LF. Happy to add it
> back if needed, but maybe a better version would be:
>
> /* Strip newline; setting password won't work if one is present. */

Good point. Yes please.

Mark