[PATCH] Return NULL instead of FAIL when retrieving a network property that has not been defined

[Francisco Munoz]

Currently, the Supplicant returns `FAIL` when trying to get or duplicate a string field on a network that is NULL. The supplicant also returns "FAIL" for other reasons as well, such as not being able to allocate memory while trying to retrieve the field. This can cause confusion as the caller is unsure if there was an error or if the field is not set.

This patch updates the Supplicant to return "NULL" when a string field is not set on a network, allowing the caller to distinguish between an error and a non-present value. The patch is inline below and attached. 

Signed-off-by: Francisco Munoz <Francisco.munozpena at microsoft.com>

---
 wpa_supplicant/config.c     | 15 ++++++++++--
 wpa_supplicant/ctrl_iface.c | 46 +++++++++++++++++++++++++++++--------
 2 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/wpa_supplicant/config.c b/wpa_supplicant/config.c
index 7a62f96..5db352e 100644
--- a/wpa_supplicant/config.c
+++ b/wpa_supplicant/config.c
@@ -183,8 +183,11 @@ static char * wpa_config_write_str(const struct parse_data *data,
 	char **src;
 
 	src = (char **) (((u8 *) ssid) + (long) data->param1);
-	if (*src == NULL)
+	if (*src == NULL) {
+		// The field is not set, set errno and return NULL
+		errno = -ENOENT;
 		return NULL;
+	}
 
 	if (data->param2)
 		len = *((size_t *) (((u8 *) ssid) + (long) data->param2));
@@ -592,6 +595,8 @@ static char * wpa_config_write_psk(const struct parse_data *data,
 	if (ssid->psk_set)
 		return wpa_config_write_string_hex(ssid->psk, PMK_LEN);
 
+	// No PSK, set errno return NULL
+	errno = -ENOENT;
 	return NULL;
 }
 #endif /* NO_CONFIG_WRITE */
@@ -1567,8 +1572,11 @@ static char * wpa_config_write_eap(const struct parse_data *data,
 	const struct eap_method_type *eap_methods = ssid->eap.eap_methods;
 	const char *name;
 
-	if (eap_methods == NULL)
+	if (eap_methods == NULL) {
+		// The field is not set, set errno and return NULL
+		errno = -ENOENT;
 		return NULL;
+	}
 
 	pos = buf = os_zalloc(100);
 	if (buf == NULL)
@@ -3125,7 +3133,10 @@ char * wpa_config_get_no_key(struct wpa_ssid *ssid, const char *var)
 					return os_strdup("*");
 				}
 
+				// Preserve errno
+				int error = errno;
 				os_free(res);
+				errno = error;
 				return NULL;
 			}
 			return res;
diff --git a/wpa_supplicant/ctrl_iface.c b/wpa_supplicant/ctrl_iface.c
index 8d5532d..104b192 100644
--- a/wpa_supplicant/ctrl_iface.c
+++ b/wpa_supplicant/ctrl_iface.c
@@ -3492,11 +3492,19 @@ static int wpa_supplicant_ctrl_iface_get_network(
 		return -1;
 	}
 
+	errno = 0;
 	value = wpa_config_get_no_key(ssid, name);
 	if (value == NULL) {
-		wpa_printf(MSG_EXCESSIVE, "CTRL_IFACE: Failed to get network "
-			   "variable '%s'", name);
-		return -1;
+		int ret = -1;
+		if (errno == -ENOENT) {
+			wpa_printf(MSG_EXCESSIVE, "CTRL_IFACE: Network variable '%s' "
+			   "is unset", name);
+			ret = -ENOENT;
+		} else {
+			wpa_printf(MSG_EXCESSIVE, "CTRL_IFACE: Failed to get network "
+				"variable '%s'", name);
+		}
+		return ret;
 	}
 
 	res = os_strlcpy(buf, value, buflen);
@@ -3553,9 +3561,16 @@ static int wpa_supplicant_ctrl_iface_dup_network(
 
 	value = wpa_config_get(ssid_s, name);
 	if (value == NULL) {
-		wpa_printf(MSG_DEBUG, "CTRL_IFACE: Failed to get network "
-			   "variable '%s'", name);
-		return -1;
+		int ret = -1;
+		if (errno == -ENOENT) {
+			wpa_printf(MSG_EXCESSIVE, "CTRL_IFACE: Network variable '%s' "
+			   "is unset", name);
+			ret = -ENOENT;
+		} else {
+			wpa_printf(MSG_EXCESSIVE, "CTRL_IFACE: Failed to get network "
+				"variable '%s'", name);
+		}
+		return ret;
 	}
 
 	ret = wpa_supplicant_ctrl_iface_update_network(dst_wpa_s, ssid_d, name,
@@ -10423,10 +10438,23 @@ char * wpa_supplicant_ctrl_iface_process(struct wpa_supplicant *wpa_s,
 	} else if (os_strncmp(buf, "GET_NETWORK ", 12) == 0) {
 		reply_len = wpa_supplicant_ctrl_iface_get_network(
 			wpa_s, buf + 12, reply, reply_size);
+		if (reply_len < 0) {
+			if (abs(reply_len) == ENOENT) {
+				os_memcpy(reply, "NULL\n", 5);
+				reply_len = 5;
+			}
+		}
 	} else if (os_strncmp(buf, "DUP_NETWORK ", 12) == 0) {
-		if (wpa_supplicant_ctrl_iface_dup_network(wpa_s, buf + 12,
-							  wpa_s))
-			reply_len = -1;
+		int ret = wpa_supplicant_ctrl_iface_dup_network(wpa_s, buf + 12,
+							  wpa_s);
+		if (ret < 0) {
+			if (abs(ret) == ENOENT) {
+				os_memcpy(reply, "NULL\n", 5);
+				reply_len = 5;
+			} else {
+				reply_len = ret;
+			}
+		}
 	} else if (os_strcmp(buf, "LIST_CREDS") == 0) {
 		reply_len = wpa_supplicant_ctrl_iface_list_creds(
 			wpa_s, reply, reply_size);
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