[PATCH 6.1.y] platform/x86: think-lmi: Fix certificate thumbprint sysfs output

[Sasha Levin <sashal@kernel.org>]

From: Thorsten Blum <thorsten.blum@linux.dev>

[ Upstream commit 4f3183f5ae9b8ddfe338d79a96146a05342bbe50 ]

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>
Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Link: https://patch.msgid.link/20260810120556.149416-2-thorsten.blum@linux.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[ Adapted upstream loop changes to the older driver’s three explicit cert_thumbprint() calls. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/platform/x86/think-lmi.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/think-lmi.c b/drivers/platform/x86/think-lmi.c
index e7605bc97f2b0..31f545a2f0a58 100644
--- a/drivers/platform/x86/think-lmi.c
+++ b/drivers/platform/x86/think-lmi.c
@@ -681,9 +681,15 @@ static ssize_t certificate_thumbprint_show(struct kobject *kobj, struct kobj_att
 	if (!tlmi_priv.certificate_support || !setting->cert_installed)
 		return -EOPNOTSUPP;
 
-	count += cert_thumbprint(buf, "Md5", count);
-	count += cert_thumbprint(buf, "Sha1", count);
-	count += cert_thumbprint(buf, "Sha256", count);
+	count = cert_thumbprint(buf, "Md5", count);
+	if (count < 0)
+		return count;
+
+	count = cert_thumbprint(buf, "Sha1", count);
+	if (count < 0)
+		return count;
+
+	count = cert_thumbprint(buf, "Sha256", count);
 	return count;
 }
 
-- 
2.53.0