[PATCH] platform/x86: think-lmi: Fix certificate thumbprint sysfs output

[Thorsten Blum <thorsten.blum@linux.dev>]

cert_thumbprint() already returns the accumulated output length, but
certificate_thumbprint_show() adds that value to count again, making the
next line use the wrong offset. Errors returned by cert_thumbprint() are
also ignored and their negative values added to count.

Assign the total length to count instead and propagate errors correctly.

Fixes: b49f72e7f96d ("platform/x86: think-lmi: Certificate authentication support")
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, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/lenovo/think-lmi.c b/drivers/platform/x86/lenovo/think-lmi.c
index e215e86e3db7..441fca37b523 100644
--- a/drivers/platform/x86/lenovo/think-lmi.c
+++ b/drivers/platform/x86/lenovo/think-lmi.c
@@ -745,6 +745,8 @@ static ssize_t certificate_thumbprint_show(struct kobject *kobj, struct kobj_att
 		return -EOPNOTSUPP;
 
 	for (i = 0; i < ARRAY_SIZE(thumbtypes); i++) {
+		ssize_t ret;
+
 		if (tlmi_priv.pwdcfg.core.password_mode >= TLMI_PWDCFG_MODE_MULTICERT) {
 			/* Format: 'SVC | SMC, Thumbtype' */
 			wmistr = kasprintf(GFP_KERNEL, "%s,%s",
@@ -756,8 +758,12 @@ static ssize_t certificate_thumbprint_show(struct kobject *kobj, struct kobj_att
 		}
 		if (!wmistr)
 			return -ENOMEM;
-		count += cert_thumbprint(buf, wmistr, count);
+
+		ret = cert_thumbprint(buf, wmistr, count);
 		kfree(wmistr);
+		if (ret < 0)
+			return ret;
+		count = ret;
 	}
 
 	return count;