[PATCH 16/16] shared/gatt-helpers: Improve robustness of get descriptors

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This patch makes sure that we do get into infinite loop when doing
get descriptors operation.

It could happen if we got bogus find information response
---
 src/shared/gatt-helpers.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/shared/gatt-helpers.c b/src/shared/gatt-helpers.c
index 6e5cf30..39ba636 100644
--- a/src/shared/gatt-helpers.c
+++ b/src/shared/gatt-helpers.c
@@ -1460,10 +1460,22 @@ static void discover_descs_cb(uint8_t opcode, const void *pdu,
 	}
 
 	last_handle = get_le16(pdu + length - data_length);
+
+	/*
+	 * If last handle is lower from previous start handle then it is smth
+	 * wrong. Let's stop search, otherwise we might enter infinite loop.
+	 */
+	if (last_handle < op->start_handle) {
+		success = false;
+		goto done;
+	}
+
+	op->start_handle = last_handle + 1;
+
 	if (last_handle != op->end_handle) {
 		uint8_t pdu[4];
 
-		put_le16(last_handle + 1, pdu);
+		put_le16(op->start_handle, pdu);
 		put_le16(op->end_handle, pdu + 2);
 
 		op->id = bt_att_send(op->att, BT_ATT_OP_FIND_INFO_REQ,
@@ -1505,6 +1517,7 @@ bool bt_gatt_discover_descriptors(struct bt_att *att,
 	op->callback = callback;
 	op->user_data = user_data;
 	op->destroy = destroy;
+	op->start_handle = start;
 	op->end_handle = end;
 
 	put_le16(start, pdu);
-- 
1.8.4

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