gatchat: fix g_at_chat_unref in notify handler

Commit Message

Maxim Lyubimov Jan. 23, 2024, 3 p.m. UTC

If the new_bytes handler processes a modem shutdown URC, it results in
a call to the g_at_chat_unref function, which includes a call to the
chat_cleanup function, which clears the list of URC handlers that
continue to be traversed after the current handler has completed, and
may lead to errors. To correct the situation, the chat_cleanup function
is not called in the at_chat_unref function if the in_read_handler flag
is set. In the new_bytes function, if the destroyed flag is set, the
chat_cleanup function is called before calling g_free. Additional
checks have been added to the chat_cleanup function.
---
 gatchat/gatchat.c | 102 +++++++++++++++++++++++++++-------------------
 1 file changed, 60 insertions(+), 42 deletions(-)

Comments

Denis Kenzior Jan. 24, 2024, 4:52 p.m. UTC | #1

Hi Maxim,

On 1/23/24 09:00, Maxim Lyubimov wrote:
> If the new_bytes handler processes a modem shutdown URC, it results in
> a call to the g_at_chat_unref function, which includes a call to the
> chat_cleanup function, which clears the list of URC handlers that
> continue to be traversed after the current handler has completed, and
> may lead to errors. To correct the situation, the chat_cleanup function
> is not called in the at_chat_unref function if the in_read_handler flag
> is set. In the new_bytes function, if the destroyed flag is set, the
> chat_cleanup function is called before calling g_free. Additional
> checks have been added to the chat_cleanup function.
> ---
>   gatchat/gatchat.c | 102 +++++++++++++++++++++++++++-------------------
>   1 file changed, 60 insertions(+), 42 deletions(-)
> 

Looks good.  There's no need to move some of these functions around now though. 
I sent a (much smaller) v3 of this patch so it goes through CI.  Please take a 
look as well.

Regards,
-Denis

Patch

diff --git a/gatchat/gatchat.c b/gatchat/gatchat.c
index 9e777107..50f8ba57 100644
--- a/gatchat/gatchat.c
+++ b/gatchat/gatchat.c
@@ -319,19 +319,25 @@  static void chat_cleanup(struct at_chat *chat)
 	struct at_command *c;
 
 	/* Cleanup pending commands */
-	while ((c = g_queue_pop_head(chat->command_queue)))
-		at_command_destroy(c);
+	if (chat->command_queue) {
+		while ((c = g_queue_pop_head(chat->command_queue)))
+			at_command_destroy(c);
 
-	g_queue_free(chat->command_queue);
-	chat->command_queue = NULL;
+		g_queue_free(chat->command_queue);
+		chat->command_queue = NULL;
+	}
 
 	/* Cleanup any response lines we have pending */
-	g_slist_free_full(chat->response_lines, g_free);
-	chat->response_lines = NULL;
+	if (chat->response_lines) {
+		g_slist_free_full(chat->response_lines, g_free);
+		chat->response_lines = NULL;
+	}
 
 	/* Cleanup registered notifications */
-	g_hash_table_destroy(chat->notify_list);
-	chat->notify_list = NULL;
+	if (chat->notify_list) {
+		g_hash_table_destroy(chat->notify_list);
+		chat->notify_list = NULL;
+	}
 
 	if (chat->pdu_notify) {
 		g_free(chat->pdu_notify);
@@ -727,6 +733,48 @@  static char *extract_line(struct at_chat *p, struct ring_buffer *rbuf)
 	return line;
 }
 
+static void at_chat_suspend(struct at_chat *chat)
+{
+	chat->suspended = TRUE;
+
+	g_at_io_set_write_handler(chat->io, NULL, NULL);
+	g_at_io_set_read_handler(chat->io, NULL, NULL);
+	g_at_io_set_debug(chat->io, NULL, NULL);
+}
+
+static struct at_chat *at_chat_ref(struct at_chat *chat)
+{
+	if (chat == NULL)
+		return NULL;
+
+	g_atomic_int_inc(&chat->ref_count);
+
+	return chat;
+}
+
+static void at_chat_unref(struct at_chat *chat)
+{
+	gboolean is_zero;
+
+	is_zero = g_atomic_int_dec_and_test(&chat->ref_count);
+
+	if (is_zero == FALSE)
+		return;
+
+	if (chat->io) {
+		at_chat_suspend(chat);
+		g_at_io_unref(chat->io);
+		chat->io = NULL;
+	}
+
+	if (chat->in_read_handler)
+		chat->destroyed = TRUE;
+	else {
+		chat_cleanup(chat);
+		g_free(chat);
+	}
+}
+
 static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
 {
 	struct at_chat *p = user_data;
@@ -780,8 +828,10 @@  static void new_bytes(struct ring_buffer *rbuf, gpointer user_data)
 
 	p->in_read_handler = FALSE;
 
-	if (p->destroyed)
+	if (p->destroyed) {
+		chat_cleanup(p);
 		g_free(p);
+	}
 }
 
 static void wakeup_cb(gboolean ok, GAtResult *result, gpointer user_data)
@@ -931,15 +981,6 @@  static void chat_wakeup_writer(struct at_chat *chat)
 	g_at_io_set_write_handler(chat->io, can_write_data, chat);
 }
 
-static void at_chat_suspend(struct at_chat *chat)
-{
-	chat->suspended = TRUE;
-
-	g_at_io_set_write_handler(chat->io, NULL, NULL);
-	g_at_io_set_read_handler(chat->io, NULL, NULL);
-	g_at_io_set_debug(chat->io, NULL, NULL);
-}
-
 static void at_chat_resume(struct at_chat *chat)
 {
 	chat->suspended = FALSE;
@@ -958,28 +999,6 @@  static void at_chat_resume(struct at_chat *chat)
 		chat_wakeup_writer(chat);
 }
 
-static void at_chat_unref(struct at_chat *chat)
-{
-	gboolean is_zero;
-
-	is_zero = g_atomic_int_dec_and_test(&chat->ref_count);
-
-	if (is_zero == FALSE)
-		return;
-
-	if (chat->io) {
-		at_chat_suspend(chat);
-		g_at_io_unref(chat->io);
-		chat->io = NULL;
-		chat_cleanup(chat);
-	}
-
-	if (chat->in_read_handler)
-		chat->destroyed = TRUE;
-	else
-		g_free(chat);
-}
-
 static gboolean at_chat_set_disconnect_function(struct at_chat *chat,
 						GAtDisconnectFunc disconnect,
 						gpointer user_data)
@@ -1372,10 +1391,9 @@  GAtChat *g_at_chat_clone(GAtChat *clone)
 	if (chat == NULL)
 		return NULL;
 
-	chat->parent = clone->parent;
+	chat->parent = at_chat_ref(clone->parent);
 	chat->group = chat->parent->next_gid++;
 	chat->ref_count = 1;
-	g_atomic_int_inc(&chat->parent->ref_count);
 
 	if (clone->slave != NULL)
 		chat->slave = g_at_chat_clone(clone->slave);