[PATCH] Add default binder devices through binderfs when configured

[Hridya Valsaraju <hridya@google.com>]

If CONFIG_ANDROID_BINDERFS is set, the default binder devices
specified by CONFIG_ANDROID_BINDER_DEVICES are created in each
binderfs instance instead of global devices being created by
the binder driver.

Co-developed-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Hridya Valsaraju <hridya@google.com>
---
 drivers/android/binder.c   |  3 ++-
 drivers/android/binderfs.c | 46 ++++++++++++++++++++++++++++++++++----
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 466b6a7f8ab7..65a99ac26711 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -6279,7 +6279,8 @@ static int __init binder_init(void)
 				    &transaction_log_fops);
 	}
 
-	if (strcmp(binder_devices_param, "") != 0) {
+	if (!IS_ENABLED(CONFIG_ANDROID_BINDERFS) &&
+	    strcmp(binder_devices_param, "") != 0) {
 		/*
 		* Copy the module_parameter string, because we don't want to
 		* tokenize it in-place.
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index e773f45d19d9..9f5ed50ffd70 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -48,6 +48,10 @@ static dev_t binderfs_dev;
 static DEFINE_MUTEX(binderfs_minors_mutex);
 static DEFINE_IDA(binderfs_minors);
 
+static char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
+module_param_named(devices, binder_devices_param, charp, 0444);
+MODULE_PARM_DESC(devices, "Binder devices to be created by default");
+
 /**
  * binderfs_mount_opts - mount options for binderfs
  * @max: maximum number of allocatable binderfs binder devices
@@ -135,7 +139,6 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
 #else
 	bool use_reserve = true;
 #endif
-
 	/* Reserve new minor number for the new device. */
 	mutex_lock(&binderfs_minors_mutex);
 	if (++info->device_count <= info->mount_opts.max)
@@ -186,8 +189,7 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
 	req->major = MAJOR(binderfs_dev);
 	req->minor = minor;
 
-	ret = copy_to_user(userp, req, sizeof(*req));
-	if (ret) {
+	if (userp && copy_to_user(userp, req, sizeof(*req))) {
 		ret = -EFAULT;
 		goto err;
 	}
@@ -467,6 +469,9 @@ static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
 	int ret;
 	struct binderfs_info *info;
 	struct inode *inode = NULL;
+	struct binderfs_device device_info = { 0 };
+	const char *name;
+	size_t len;
 
 	sb->s_blocksize = PAGE_SIZE;
 	sb->s_blocksize_bits = PAGE_SHIFT;
@@ -521,7 +526,28 @@ static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
 	if (!sb->s_root)
 		return -ENOMEM;
 
-	return binderfs_binder_ctl_create(sb);
+	ret = binderfs_binder_ctl_create(sb);
+	if (ret)
+		return ret;
+
+	name = binder_devices_param;
+	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
+		/*
+		 * init_binderfs() has already checked that the length of
+		 * device_name_entry->name is not greater than device_info.name.
+		 */
+		strscpy(device_info.name, name, len + 1);
+		ret = binderfs_binder_device_create(inode, NULL, &device_info);
+		if (ret)
+			return ret;
+		name += len;
+		if (*name == ',')
+			name++;
+
+	}
+
+	return 0;
+
 }
 
 static struct dentry *binderfs_mount(struct file_system_type *fs_type,
@@ -553,6 +579,18 @@ static struct file_system_type binder_fs_type = {
 int __init init_binderfs(void)
 {
 	int ret;
+	const char *name;
+	size_t len;
+
+	/* Verify that the default binderfs device names are valid. */
+	name = binder_devices_param;
+	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
+		if (len > BINDERFS_MAX_NAME)
+			return -E2BIG;
+		name += len;
+		if (*name == ',')
+			name++;
+	}
 
 	/* Allocate new major number for binderfs. */
 	ret = alloc_chrdev_region(&binderfs_dev, 0, BINDERFS_MAX_MINOR,
-- 
2.22.0.770.g0f2c4a37fd-goog