[PATCH v4 4/9] platform/x86: hp-bioscfg: allow clearing current_password

[Muhammad Bilal <meatuni001@gmail.com>]

The ABI documents echo "" > current_password as the way to end a
session, but validate_password_input() rejects an empty string when
min_password_length is nonzero. The password stays cached, and since
the previous patch the write also fails with -E2BIG.

Skip the length check for an empty current_password so the write
clears it.

Before the previous patch the write returned 1 on an HP EliteBook 840
G2 (min_password_length is 8) but cleared nothing.

Compile tested only.

Fixes: 8646a3b5ee3a ("platform/x86: hp-bioscfg: passwdobj-attributes")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
Changes in v4:
 - New patch

 .../platform/x86/hp/hp-bioscfg/passwdobj-attributes.c    | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/hp/hp-bioscfg/passwdobj-attributes.c b/drivers/platform/x86/hp/hp-bioscfg/passwdobj-attributes.c
index 3f4c45d9b..f0551b455 100644
--- a/drivers/platform/x86/hp/hp-bioscfg/passwdobj-attributes.c
+++ b/drivers/platform/x86/hp/hp-bioscfg/passwdobj-attributes.c
@@ -60,7 +60,8 @@ int hp_get_password_instance_for_type(const char *name)
 	return -EINVAL;
 }
 
-static int validate_password_input(int instance_id, const char *buf)
+static int validate_password_input(int instance_id, const char *buf,
+				   bool is_current)
 {
 	int length;
 	struct password_data *password_data = &bioscfg_drv.password_data[instance_id];
@@ -69,6 +70,10 @@ static int validate_password_input(int instance_id, const char *buf)
 	if (length > 0 && buf[length - 1] == '\n')
 		length--;
 
+	/* An empty current_password clears the session password */
+	if (is_current && !length)
+		return 0;
+
 	if (length > MAX_PASSWD_SIZE)
 		return -E2BIG;
 
@@ -97,7 +102,7 @@ static int store_password_instance(struct kobject *kobj, const char *buf,
 		id = get_password_instance_id(kobj);
 
 		if (id >= 0)
-			ret = validate_password_input(id, buf_cp);
+			ret = validate_password_input(id, buf_cp, is_current);
 	}
 
 	if (!ret) {
-- 
2.43.0