From 591c546c536b42bef696d027f64aa22434f8c3f0 Mon Sep 17 00:00:00 2001
From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date: Tue, 8 Jun 2021 16:46:49 -0700
Subject: [PATCH] shared/gatt-server: Fix heap overflow when appending prepare
 writes

The code shall check if the prepare writes would append more the
allowed maximum attribute length.

Fixes https://github.com/bluez/bluez/security/advisories/GHSA-479m-xcq5-9g2q
---
 src/shared/gatt-server.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/shared/gatt-server.c b/src/shared/gatt-server.c
index dc4e681c9c..9beec44bed 100644
--- a/src/shared/gatt-server.c
+++ b/src/shared/gatt-server.c
@@ -779,6 +779,20 @@ static uint8_t authorize_req(struct bt_gatt_server *server,
 						server->authorize_data);
 }
 
+static uint8_t check_length(uint16_t length, uint16_t offset)
+{
+	if (length > BT_ATT_MAX_VALUE_LEN)
+		return BT_ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LEN;
+
+	if (offset > BT_ATT_MAX_VALUE_LEN)
+		return BT_ATT_ERROR_INVALID_OFFSET;
+
+	if (length + offset > BT_ATT_MAX_VALUE_LEN)
+		return BT_ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LEN;
+
+	return 0;
+}
+
 static void write_cb(struct bt_att_chan *chan, uint8_t opcode, const void *pdu,
 					uint16_t length, void *user_data)
 {
@@ -809,6 +823,10 @@ static void write_cb(struct bt_att_chan *chan, uint8_t opcode, const void *pdu,
 				(opcode == BT_ATT_OP_WRITE_REQ) ? "Req" : "Cmd",
 				handle);
 
+	ecode = check_length(length, 0);
+	if (ecode)
+		goto error;
+
 	ecode = check_permissions(server, attr, BT_ATT_PERM_WRITE_MASK);
 	if (ecode)
 		goto error;
@@ -1299,6 +1317,10 @@ static void prep_write_cb(struct bt_att_chan *chan, uint8_t opcode,
 	util_debug(server->debug_callback, server->debug_data,
 				"Prep Write Req - handle: 0x%04x", handle);
 
+	ecode = check_length(length, offset);
+	if (ecode)
+		goto error;
+
 	ecode = check_permissions(server, attr, BT_ATT_PERM_WRITE_MASK);
 	if (ecode)
 		goto error;
