[RFC PATCH BlueZ v2] Cleaning up gatt operations on a disconnect to fix possible use after free

There is a current use after free possible on a gatt server if a client
disconnects while a WriteValue call is being processed with dbus.

This patch includes the addition of a pending disconnect callback to handle
cleanup better if a disconnect occurs during a write, an acquire write
or read operation using bt_att_register_disconnect with the cb.

v2: Fixed a bad call to pending_read_new

---
 src/gatt-database.c | 115 +++++++++++++++++++++++++-------------------
 1 file changed, 65 insertions(+), 50 deletions(-)

diff --git a/src/gatt-database.c b/src/gatt-database.c
index 1f7ce5f02..a03c579cf 100644
--- a/src/gatt-database.c
+++ b/src/gatt-database.c

@@ -933,6 +933,24 @@ static struct btd_device *att_get_device(struct bt_att *att)
 	return btd_adapter_find_device(adapter, &dst, dst_type);
 }
 
+
+static void pending_op_free(void *data)
+{
+	struct pending_op *op = data;
+
+	if (op->owner_queue)
+		queue_remove(op->owner_queue, op);
+
+	free(op);
+}
+
+static void pending_disconnect_cb(int err, void *user_data)
+{
+	struct pending_op *op = user_data;
+
+	op->owner_queue = NULL;
+}
+
 static struct pending_op *pending_ccc_new(struct bt_att *att,
 					struct gatt_db_attribute *attrib,
 					uint16_t value,

@@ -956,17 +974,12 @@ static struct pending_op *pending_ccc_new(struct bt_att *att,
 	op->attrib = attrib;
 	op->link_type = link_type;
 
-	return op;
-}
+	bt_att_register_disconnect(att,
+				   pending_disconnect_cb,
+				   op,
+				   NULL);
 
-static void pending_op_free(void *data)
-{
-	struct pending_op *op = data;
-
-	if (op->owner_queue)
-		queue_remove(op->owner_queue, op);
-
-	free(op);
+	return op;
 }
 
 static void gatt_ccc_write_cb(struct gatt_db_attribute *attrib,

@@ -2169,24 +2182,26 @@ done:
 	gatt_db_attribute_read_result(op->attrib, op->id, ecode, value, len);
 }
 
-static struct pending_op *pending_read_new(struct btd_device *device,
+
+static struct pending_op *pending_read_new(struct bt_att *att,
 					struct queue *owner_queue,
 					struct gatt_db_attribute *attrib,
-					unsigned int id, uint16_t offset,
-					uint8_t link_type)
+					unsigned int id, uint16_t offset)
 {
 	struct pending_op *op;
 
 	op = new0(struct pending_op, 1);
 
 	op->owner_queue = owner_queue;
-	op->device = device;
+	op->device = att_get_device(att);
 	op->attrib = attrib;
 	op->id = id;
 	op->offset = offset;
-	op->link_type = link_type;
+	op->link_type = bt_att_get_link_type(att);
 	queue_push_tail(owner_queue, op);
 
+	bt_att_register_disconnect(att, pending_disconnect_cb, op, NULL);
+
 	return op;
 }
 

@@ -2243,18 +2258,16 @@ static void read_setup_cb(DBusMessageIter *iter, void *user_data)
 	dbus_message_iter_close_container(iter, &dict);
 }
 
-static struct pending_op *send_read(struct btd_device *device,
+static struct pending_op *send_read(struct bt_att *att,
 					struct gatt_db_attribute *attrib,
 					GDBusProxy *proxy,
 					struct queue *owner_queue,
 					unsigned int id,
-					uint16_t offset,
-					uint8_t link_type)
+					uint16_t offset)
 {
 	struct pending_op *op;
 
-	op = pending_read_new(device, owner_queue, attrib, id, offset,
-							link_type);
+	op = pending_read_new(att, owner_queue, attrib, id, offset);
 
 	if (g_dbus_proxy_method_call(proxy, "ReadValue", read_setup_cb,
 				read_reply_cb, op, pending_op_free) == TRUE)

@@ -2337,15 +2350,17 @@ static void write_reply_cb(DBusMessage *message, void *user_data)
 	}
 
 done:
-	gatt_db_attribute_write_result(op->attrib, op->id, ecode);
+	// Make sure that only reply if the device is connected
+	if (btd_device_is_connected(op->device))
+		gatt_db_attribute_write_result(op->attrib, op->id, ecode);
 }
 
-static struct pending_op *pending_write_new(struct btd_device *device,
+static struct pending_op *pending_write_new(struct bt_att *att,
 					struct queue *owner_queue,
 					struct gatt_db_attribute *attrib,
 					unsigned int id,
 					const uint8_t *value, size_t len,
-					uint16_t offset, uint8_t link_type,
+					uint16_t offset,
 					bool is_characteristic,
 					bool prep_authorize)
 {

@@ -2356,33 +2371,37 @@ static struct pending_op *pending_write_new(struct btd_device *device,
 	op->data.iov_base = (uint8_t *) value;
 	op->data.iov_len = len;
 
-	op->device = device;
+	op->device = att_get_device(att);
 	op->owner_queue = owner_queue;
 	op->attrib = attrib;
 	op->id = id;
 	op->offset = offset;
-	op->link_type = link_type;
+	op->link_type = bt_att_get_link_type(att);
 	op->is_characteristic = is_characteristic;
 	op->prep_authorize = prep_authorize;
 	queue_push_tail(owner_queue, op);
 
+	bt_att_register_disconnect(att,
+			    pending_disconnect_cb,
+			    op, NULL);
+
 	return op;
 }
 
-static struct pending_op *send_write(struct btd_device *device,
+static struct pending_op *send_write(struct bt_att *att,
 					struct gatt_db_attribute *attrib,
 					GDBusProxy *proxy,
 					struct queue *owner_queue,
 					unsigned int id,
 					const uint8_t *value, size_t len,
-					uint16_t offset, uint8_t link_type,
+					uint16_t offset,
 					bool is_characteristic,
 					bool prep_authorize)
 {
 	struct pending_op *op;
 
-	op = pending_write_new(device, owner_queue, attrib, id, value, len,
-					offset, link_type, is_characteristic,
+	op = pending_write_new(att, owner_queue, attrib, id, value, len,
+					offset, is_characteristic,
 					prep_authorize);
 
 	if (g_dbus_proxy_method_call(proxy, "WriteValue", write_setup_cb,

@@ -2558,17 +2577,16 @@ static void acquire_write_setup(DBusMessageIter *iter, void *user_data)
 }
 
 static struct pending_op *acquire_write(struct external_chrc *chrc,
-					struct btd_device *device,
+					struct bt_att *att,
 					struct gatt_db_attribute *attrib,
 					unsigned int id,
-					const uint8_t *value, size_t len,
-					uint8_t link_type)
+					const uint8_t *value, size_t len)
 {
 	struct pending_op *op;
 	bool acquiring = !queue_isempty(chrc->pending_writes);
 
-	op = pending_write_new(device, chrc->pending_writes, attrib, id, value,
-				len, 0, link_type, false, false);
+	op = pending_write_new(att, chrc->pending_writes, attrib, id, value,
+				len, 0, false, false);
 
 	if (acquiring)
 		return op;

@@ -2851,8 +2869,8 @@ static void desc_read_cb(struct gatt_db_attribute *attrib,
 		goto fail;
 	}
 
-	if (send_read(device, attrib, desc->proxy, desc->pending_reads, id,
-					offset, bt_att_get_link_type(att)))
+	if (send_read(att, attrib, desc->proxy, desc->pending_reads, id,
+					offset))
 		return;
 
 fail:

@@ -2883,10 +2901,9 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
 	if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
 		if (!device_is_trusted(device) && !desc->prep_authorized &&
 						desc->req_prep_authorization)
-			send_write(device, attrib, desc->proxy,
+			send_write(att, attrib, desc->proxy,
 					desc->pending_writes, id, value, len,
-					offset, bt_att_get_link_type(att),
-					false, true);
+					offset, false, true);
 		else
 			gatt_db_attribute_write_result(attrib, id, 0);
 

@@ -2896,9 +2913,8 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
 	if (opcode == BT_ATT_OP_EXEC_WRITE_REQ)
 		desc->prep_authorized = false;
 
-	if (send_write(device, attrib, desc->proxy, desc->pending_writes, id,
-			value, len, offset, bt_att_get_link_type(att), false,
-			false))
+	if (send_write(att, attrib, desc->proxy, desc->pending_writes, id,
+			value, len, offset, false, false))
 		return;
 
 fail:

@@ -2977,8 +2993,8 @@ static void chrc_read_cb(struct gatt_db_attribute *attrib,
 		goto fail;
 	}
 
-	if (send_read(device, attrib, chrc->proxy, chrc->pending_reads, id,
-					offset, bt_att_get_link_type(att)))
+	if (send_read(att, attrib, chrc->proxy, chrc->pending_reads, id,
+	       offset))
 		return;
 
 fail:

@@ -3016,9 +3032,9 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
 	if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
 		if (!device_is_trusted(device) && !chrc->prep_authorized &&
 						chrc->req_prep_authorization)
-			send_write(device, attrib, chrc->proxy, queue,
+			send_write(att, attrib, chrc->proxy, queue,
 					id, value, len, offset,
-					bt_att_get_link_type(att), true, true);
+					true, true);
 		else
 			gatt_db_attribute_write_result(attrib, id, 0);
 

@@ -3039,13 +3055,12 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
 	}
 
 	if (g_dbus_proxy_get_property(chrc->proxy, "WriteAcquired", &iter)) {
-		if (acquire_write(chrc, device, attrib, id, value, len,
-						bt_att_get_link_type(att)))
+		if (acquire_write(chrc, att, attrib, id, value, len))
 			return;
 	}
 
-	if (send_write(device, attrib, chrc->proxy, queue, id, value, len,
-			offset, bt_att_get_link_type(att), false, false))
+	if (send_write(att, attrib, chrc->proxy, queue, id, value, len,
+			offset, false, false))
 		return;
 
 fail:

-- 
2.17.1

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=554607

---Test result---

Test Summary:
CheckPatch                    PASS      1.56 seconds
GitLint                       FAIL      1.05 seconds
Prep - Setup ELL              PASS      48.61 seconds
Build - Prep                  PASS      0.51 seconds
Build - Configure             PASS      8.91 seconds
Build - Make                  PASS      207.06 seconds
Make Check                    PASS      9.64 seconds
Make Distcheck                PASS      246.35 seconds
Build w/ext ELL - Configure   PASS      9.02 seconds
Build w/ext ELL - Make        PASS      195.19 seconds

Details
##############################
Test: GitLint - FAIL
Desc: Run gitlint with rule in .gitlint
Output:
[RFC,BlueZ,v2] Cleaning up gatt operations on a disconnect to fix possible use after free
1: T1 Title exceeds max length (89>80): "[RFC,BlueZ,v2] Cleaning up gatt operations on a disconnect to fix possible use after free"




---
Regards,
Linux Bluetooth

Hi Bernie,

On Tue, Sep 28, 2021 at 4:01 PM Bernie Conrad [off-list ref] wrote:

We might need to do something like the following:

https://gist.github.com/Vudentz/958d540591d1ae6a32d226ef8a0d6d54

Otherwise we risk the op being freeing when the op is completely
properly but when att is disconnected it still runs
pending_disconnect_cb causing a UAF.

-- 
Luiz Augusto von Dentz

Hi Bernie,

On Wed, Sep 29, 2021 at 2:05 PM Luiz Augusto von Dentz
[off-list ref] wrote:

Hi Bernie,

On Tue, Sep 28, 2021 at 4:01 PM Bernie Conrad [off-list ref] wrote:

quoted

There is a current use after free possible on a gatt server if a client
disconnects while a WriteValue call is being processed with dbus.

This patch includes the addition of a pending disconnect callback to handle
cleanup better if a disconnect occurs during a write, an acquire write
or read operation using bt_att_register_disconnect with the cb.

v2: Fixed a bad call to pending_read_new

---
 src/gatt-database.c | 115 +++++++++++++++++++++++++-------------------
 1 file changed, 65 insertions(+), 50 deletions(-)

diff --git a/src/gatt-database.c b/src/gatt-database.c
index 1f7ce5f02..a03c579cf 100644
--- a/src/gatt-database.c
+++ b/src/gatt-database.c

@@ -933,6 +933,24 @@ static struct btd_device *att_get_device(struct bt_att *att)
        return btd_adapter_find_device(adapter, &dst, dst_type);
 }

+
+static void pending_op_free(void *data)
+{
+       struct pending_op *op = data;
+
+       if (op->owner_queue)
+               queue_remove(op->owner_queue, op);
+
+       free(op);

We might need to do something like the following:

https://gist.github.com/Vudentz/958d540591d1ae6a32d226ef8a0d6d54

Otherwise we risk the op being freeing when the op is completely
properly but when att is disconnected it still runs
pending_disconnect_cb causing a UAF.

quoted

+}
+
+static void pending_disconnect_cb(int err, void *user_data)
+{
+       struct pending_op *op = user_data;
+
+       op->owner_queue = NULL;
+}
+
 static struct pending_op *pending_ccc_new(struct bt_att *att,
                                        struct gatt_db_attribute *attrib,
                                        uint16_t value,

@@ -956,17 +974,12 @@ static struct pending_op *pending_ccc_new(struct bt_att *att,
        op->attrib = attrib;
        op->link_type = link_type;

-       return op;
-}
+       bt_att_register_disconnect(att,
+                                  pending_disconnect_cb,
+                                  op,
+                                  NULL);

-static void pending_op_free(void *data)
-{
-       struct pending_op *op = data;
-
-       if (op->owner_queue)
-               queue_remove(op->owner_queue, op);
-
-       free(op);
+       return op;
 }

 static void gatt_ccc_write_cb(struct gatt_db_attribute *attrib,

@@ -2169,24 +2182,26 @@ done:
        gatt_db_attribute_read_result(op->attrib, op->id, ecode, value, len);
 }

-static struct pending_op *pending_read_new(struct btd_device *device,
+
+static struct pending_op *pending_read_new(struct bt_att *att,
                                        struct queue *owner_queue,
                                        struct gatt_db_attribute *attrib,
-                                       unsigned int id, uint16_t offset,
-                                       uint8_t link_type)
+                                       unsigned int id, uint16_t offset)
 {
        struct pending_op *op;

        op = new0(struct pending_op, 1);

        op->owner_queue = owner_queue;
-       op->device = device;
+       op->device = att_get_device(att);
        op->attrib = attrib;
        op->id = id;
        op->offset = offset;
-       op->link_type = link_type;
+       op->link_type = bt_att_get_link_type(att);
        queue_push_tail(owner_queue, op);

+       bt_att_register_disconnect(att, pending_disconnect_cb, op, NULL);
+
        return op;
 }

@@ -2243,18 +2258,16 @@ static void read_setup_cb(DBusMessageIter *iter, void *user_data)
        dbus_message_iter_close_container(iter, &dict);
 }

-static struct pending_op *send_read(struct btd_device *device,
+static struct pending_op *send_read(struct bt_att *att,
                                        struct gatt_db_attribute *attrib,
                                        GDBusProxy *proxy,
                                        struct queue *owner_queue,
                                        unsigned int id,
-                                       uint16_t offset,
-                                       uint8_t link_type)
+                                       uint16_t offset)
 {
        struct pending_op *op;

-       op = pending_read_new(device, owner_queue, attrib, id, offset,
-                                                       link_type);
+       op = pending_read_new(att, owner_queue, attrib, id, offset);

        if (g_dbus_proxy_method_call(proxy, "ReadValue", read_setup_cb,
                                read_reply_cb, op, pending_op_free) == TRUE)

@@ -2337,15 +2350,17 @@ static void write_reply_cb(DBusMessage *message, void *user_data)
        }

 done:
-       gatt_db_attribute_write_result(op->attrib, op->id, ecode);
+       // Make sure that only reply if the device is connected
+       if (btd_device_is_connected(op->device))
+               gatt_db_attribute_write_result(op->attrib, op->id, ecode);
 }

-static struct pending_op *pending_write_new(struct btd_device *device,
+static struct pending_op *pending_write_new(struct bt_att *att,
                                        struct queue *owner_queue,
                                        struct gatt_db_attribute *attrib,
                                        unsigned int id,
                                        const uint8_t *value, size_t len,
-                                       uint16_t offset, uint8_t link_type,
+                                       uint16_t offset,
                                        bool is_characteristic,
                                        bool prep_authorize)
 {

@@ -2356,33 +2371,37 @@ static struct pending_op *pending_write_new(struct btd_device *device,
        op->data.iov_base = (uint8_t *) value;
        op->data.iov_len = len;

-       op->device = device;
+       op->device = att_get_device(att);
        op->owner_queue = owner_queue;
        op->attrib = attrib;
        op->id = id;
        op->offset = offset;
-       op->link_type = link_type;
+       op->link_type = bt_att_get_link_type(att);
        op->is_characteristic = is_characteristic;
        op->prep_authorize = prep_authorize;
        queue_push_tail(owner_queue, op);

+       bt_att_register_disconnect(att,
+                           pending_disconnect_cb,
+                           op, NULL);
+
        return op;
 }

-static struct pending_op *send_write(struct btd_device *device,
+static struct pending_op *send_write(struct bt_att *att,
                                        struct gatt_db_attribute *attrib,
                                        GDBusProxy *proxy,
                                        struct queue *owner_queue,
                                        unsigned int id,
                                        const uint8_t *value, size_t len,
-                                       uint16_t offset, uint8_t link_type,
+                                       uint16_t offset,
                                        bool is_characteristic,
                                        bool prep_authorize)
 {
        struct pending_op *op;

-       op = pending_write_new(device, owner_queue, attrib, id, value, len,
-                                       offset, link_type, is_characteristic,
+       op = pending_write_new(att, owner_queue, attrib, id, value, len,
+                                       offset, is_characteristic,
                                        prep_authorize);

        if (g_dbus_proxy_method_call(proxy, "WriteValue", write_setup_cb,

@@ -2558,17 +2577,16 @@ static void acquire_write_setup(DBusMessageIter *iter, void *user_data)
 }

 static struct pending_op *acquire_write(struct external_chrc *chrc,
-                                       struct btd_device *device,
+                                       struct bt_att *att,
                                        struct gatt_db_attribute *attrib,
                                        unsigned int id,
-                                       const uint8_t *value, size_t len,
-                                       uint8_t link_type)
+                                       const uint8_t *value, size_t len)
 {
        struct pending_op *op;
        bool acquiring = !queue_isempty(chrc->pending_writes);

-       op = pending_write_new(device, chrc->pending_writes, attrib, id, value,
-                               len, 0, link_type, false, false);
+       op = pending_write_new(att, chrc->pending_writes, attrib, id, value,
+                               len, 0, false, false);

        if (acquiring)
                return op;

@@ -2851,8 +2869,8 @@ static void desc_read_cb(struct gatt_db_attribute *attrib,
                goto fail;
        }

-       if (send_read(device, attrib, desc->proxy, desc->pending_reads, id,
-                                       offset, bt_att_get_link_type(att)))
+       if (send_read(att, attrib, desc->proxy, desc->pending_reads, id,
+                                       offset))
                return;

 fail:

@@ -2883,10 +2901,9 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
        if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
                if (!device_is_trusted(device) && !desc->prep_authorized &&
                                                desc->req_prep_authorization)
-                       send_write(device, attrib, desc->proxy,
+                       send_write(att, attrib, desc->proxy,
                                        desc->pending_writes, id, value, len,
-                                       offset, bt_att_get_link_type(att),
-                                       false, true);
+                                       offset, false, true);
                else
                        gatt_db_attribute_write_result(attrib, id, 0);

@@ -2896,9 +2913,8 @@ static void desc_write_cb(struct gatt_db_attribute *attrib,
        if (opcode == BT_ATT_OP_EXEC_WRITE_REQ)
                desc->prep_authorized = false;

-       if (send_write(device, attrib, desc->proxy, desc->pending_writes, id,
-                       value, len, offset, bt_att_get_link_type(att), false,
-                       false))
+       if (send_write(att, attrib, desc->proxy, desc->pending_writes, id,
+                       value, len, offset, false, false))
                return;

 fail:

@@ -2977,8 +2993,8 @@ static void chrc_read_cb(struct gatt_db_attribute *attrib,
                goto fail;
        }

-       if (send_read(device, attrib, chrc->proxy, chrc->pending_reads, id,
-                                       offset, bt_att_get_link_type(att)))
+       if (send_read(att, attrib, chrc->proxy, chrc->pending_reads, id,
+              offset))
                return;

 fail:

@@ -3016,9 +3032,9 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
        if (opcode == BT_ATT_OP_PREP_WRITE_REQ) {
                if (!device_is_trusted(device) && !chrc->prep_authorized &&
                                                chrc->req_prep_authorization)
-                       send_write(device, attrib, chrc->proxy, queue,
+                       send_write(att, attrib, chrc->proxy, queue,
                                        id, value, len, offset,
-                                       bt_att_get_link_type(att), true, true);
+                                       true, true);
                else
                        gatt_db_attribute_write_result(attrib, id, 0);

@@ -3039,13 +3055,12 @@ static void chrc_write_cb(struct gatt_db_attribute *attrib,
        }

        if (g_dbus_proxy_get_property(chrc->proxy, "WriteAcquired", &iter)) {
-               if (acquire_write(chrc, device, attrib, id, value, len,
-                                               bt_att_get_link_type(att)))
+               if (acquire_write(chrc, att, attrib, id, value, len))
                        return;
        }

-       if (send_write(device, attrib, chrc->proxy, queue, id, value, len,
-                       offset, bt_att_get_link_type(att), false, false))
+       if (send_write(att, attrib, chrc->proxy, queue, id, value, len,
+                       offset, false, false))
                return;

 fail:
--

2.17.1

--
Luiz Augusto von Dentz

I went ahead and applied this with my changes on top, thanks.

-- 
Luiz Augusto von Dentz