Commit 84265cbd authored by Damien Riégel's avatar Damien Riégel Committed by Greg Kroah-Hartman
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greybus: raw: fix use-after-free if write is called after disconnect 



If a user writes to the chardev after disconnect has been called, the
kernel panics with the following trace (with
CONFIG_INIT_ON_FREE_DEFAULT_ON=y):

        BUG: kernel NULL pointer dereference, address: 0000000000000218
         ...
        Call Trace:
         <TASK>
         gb_operation_create_common+0x61/0x180
         gb_operation_create_flags+0x28/0xa0
         gb_operation_sync_timeout+0x6f/0x100
         raw_write+0x7b/0xc7 [gb_raw]
         vfs_write+0xcf/0x420
         ? task_mm_cid_work+0x136/0x220
         ksys_write+0x63/0xe0
         do_syscall_64+0xa4/0x290
         entry_SYSCALL_64_after_hwframe+0x77/0x7f

Disconnect calls gb_connection_destroy, which ends up freeing the
connection object. When gb_operation_sync is called in the write file
operations, its gets a freed connection as parameter and the kernel
panics.

The gb_connection_destroy cannot be moved out of the disconnect
function, as the Greybus subsystem expect all connections belonging to a
bundle to be destroyed when disconnect returns.

To prevent this bug, use a rw lock to synchronize access between write
and disconnect. This guarantees that the write function doesn't try
to use a disconnected connection.

Fixes: e806c7fb ("greybus: raw: add raw greybus kernel driver")
Reviewed-by: default avatarJohan Hovold <johan@kernel.org>
Signed-off-by: default avatarDamien Riégel <damien.riegel@silabs.com>
Link: https://patch.msgid.link/20260324140039.40001-2-damien.riegel@silabs.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 983cc2c7

drivers/staging/greybus/raw.c

+21 −2
Original line number Diff line number Diff line
@@ -21,6 +21,8 @@ struct gb_raw { 
	struct list_head list;

	int list_data;

	struct mutex list_lock;

	struct rw_semaphore disconnect_lock;

	bool disconnected;

	struct cdev cdev;

	struct device dev;

};
@@ -200,6 +202,7 @@ static int gb_raw_probe(struct gb_bundle *bundle, 


	INIT_LIST_HEAD(&raw->list);

	mutex_init(&raw->list_lock);

	init_rwsem(&raw->disconnect_lock);



	raw->connection = connection;

	greybus_set_drvdata(bundle, raw);
@@ -235,6 +238,11 @@ static void gb_raw_disconnect(struct gb_bundle *bundle) 
	struct raw_data *temp;



	cdev_device_del(&raw->cdev, &raw->dev);



	down_write(&raw->disconnect_lock);

	raw->disconnected = true;

	up_write(&raw->disconnect_lock);



	gb_connection_disable(connection);

	gb_connection_destroy(connection);
@@ -277,11 +285,22 @@ static ssize_t raw_write(struct file *file, const char __user *buf, 
	if (count > MAX_PACKET_SIZE)

		return -E2BIG;



	down_read(&raw->disconnect_lock);



	if (raw->disconnected) {

		retval = -ENODEV;

		goto exit;

	}



	retval = gb_raw_send(raw, count, buf);

	if (retval)

		return retval;

		goto exit;



	return count;

	retval = count;

exit:

	up_read(&raw->disconnect_lock);



	return retval;

}



static ssize_t raw_read(struct file *file, char __user *buf, size_t count,