binder: Validate the default binderfs device names.

Length of a binderfs device name cannot exceed BINDERFS_MAX_NAME.
This patch adds a check in binderfs_init() to ensure the same
for the default binder devices that will be created in every
binderfs instance.
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>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/20190808222727.132744-3-hridya@google.com
Link: https://lore.kernel.org/r/20190904110704.8606-3-christian.brauner@ubuntu.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binderfs.c

@@ -553,6 +553,18 @@ 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,