From 4a3a7ca0b15485a9061017409b51fc5e4cf86ecb Mon Sep 17 00:00:00 2001
From: Amin Ben Romdhane <amin.benromdhane@iopsys.eu>
Date: Thu, 24 Apr 2025 23:19:51 +0200
Subject: [PATCH] Reference DB: add file lock to prevent race condition when
 updating reference DB file

Added an exclusive file locking mechanism using `flock()` to ensure that
only one process at a time can update the '/var/state/bbfdm_reference_db' file.
This prevents data loss or corruption caused by concurrent access.

This change improves robustness when `bbfdm_refresh_references()` is called
by multiple processes in parallel.
---
 libbbfdm-api/legacy/dmbbf.c | 12 +++++++-----
 libbbfdm-ubus/bbfdm-ubus.c  | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/libbbfdm-api/legacy/dmbbf.c b/libbbfdm-api/legacy/dmbbf.c
index d85fee2b..7fb1952c 100644
--- a/libbbfdm-api/legacy/dmbbf.c
+++ b/libbbfdm-api/legacy/dmbbf.c
@@ -1921,24 +1921,26 @@ static void create_required_sections(struct dmctx *ctx)
 		dmuci_rename_section_by_section(ref_s, ctx->in_value);
 	} else {
 		struct uci_list *uci_list = NULL;
-		struct uci_element *e = NULL, *tmp = NULL;
+		struct uci_element *e = NULL;
 
 		dmuci_get_value_by_section_list(ref_s, "reference_path", &uci_list);
 		if (uci_list != NULL) {
 
-			uci_foreach_element_safe(uci_list, tmp, e) {
+			uci_foreach_element(uci_list, e) {
 				dmuci_set_value_varstate("bbfdm_reference_db", "reference_path", e->name, "");
-				dmuci_del_list_value_by_section(ref_s, "reference_path", e->name);
 			}
+
+			dmuci_set_value_by_section_varstate(ref_s, "reference_path", "");
 		}
 
 		dmuci_get_value_by_section_list(ref_s, "reference_value", &uci_list);
 		if (uci_list != NULL) {
 
-			uci_foreach_element_safe(uci_list, tmp, e) {
+			uci_foreach_element(uci_list, e) {
 				dmuci_set_value_varstate("bbfdm_reference_db", "reference_value", e->name, "");
-				dmuci_del_list_value_by_section(ref_s, "reference_value", e->name);
 			}
+
+			dmuci_set_value_by_section_varstate(ref_s, "reference_value", "");
 		}
 	}
 
diff --git a/libbbfdm-ubus/bbfdm-ubus.c b/libbbfdm-ubus/bbfdm-ubus.c
index 99c67345..b81160b5 100644
--- a/libbbfdm-ubus/bbfdm-ubus.c
+++ b/libbbfdm-ubus/bbfdm-ubus.c
@@ -12,6 +12,9 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/file.h>
 #include <libubox/blobmsg.h>
 #include <libubox/uloop.h>
 #include <libubus.h>
@@ -779,6 +782,33 @@ void bbfdm_ubus_load_data_model(DM_MAP_OBJ *DynamicObj)
 	INTERNAL_ROOT_TREE = DynamicObj;
 }
 
+static int bbfdm_lock_reference_db(void)
+{
+#define BBF_LOCK_FILE "/var/lock/bbfdm_reference_db.lock"
+
+	int fd = open(BBF_LOCK_FILE, O_CREAT | O_RDWR, 0666);
+	if (fd == -1) {
+		BBF_ERR("Error opening lock file %s: %s", BBF_LOCK_FILE, strerror(errno));
+		return -1;
+	}
+
+	if (flock(fd, LOCK_EX) == -1) {
+		BBF_ERR("Error locking file %s: %s", BBF_LOCK_FILE, strerror(errno));
+		close(fd);
+		return -1;
+	}
+
+	return fd; // Lock held
+}
+
+static void bbfdm_unlock_reference_db(int lock_fd)
+{
+	if (lock_fd >= 0) {
+		flock(lock_fd, LOCK_UN);
+		close(lock_fd);
+	}
+}
+
 int bbfdm_refresh_references(unsigned int dm_type, const char *srv_obj_name)
 {
 	char hash_str[9] = {0};
@@ -791,6 +821,10 @@ int bbfdm_refresh_references(unsigned int dm_type, const char *srv_obj_name)
 		.dm_type = dm_type
 	};
 
+	int lock_fd = bbfdm_lock_reference_db();
+	if (lock_fd == -1)
+		return -1;
+
 	bbf_init(&bbf_ctx);
 	int res = bbfdm_cmd_exec(&bbf_ctx, BBF_REFERENCES_DB);
 
@@ -804,6 +838,7 @@ int bbfdm_refresh_references(unsigned int dm_type, const char *srv_obj_name)
 	}
 
 	bbf_cleanup(&bbf_ctx);
+	bbfdm_unlock_reference_db(lock_fd);
 
 	return res;
 }