binder: Add default binder devices through binderfs when configured

Currently, since each binderfs instance needs its own
private binder devices, every time a binderfs instance is
mounted, all the default binder devices need to be created
via the BINDER_CTL_ADD IOCTL. This patch aims to
add a solution to automatically create the default binder
devices for each binderfs instance that gets mounted.
To achieve this goal, when 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>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/20190808222727.132744-2-hridya@google.com
Link: https://lore.kernel.org/r/20190904110704.8606-2-christian.brauner@ubuntu.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 25 insertions, 5 deletions

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index dc1c83eafc22..ef2d3e582368 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -122,7 +122,7 @@ static uint32_t binder_debug_mask = BINDER_DEBUG_USER_ERROR |
         BINDER_DEBUG_FAILED_TRANSACTION | BINDER_DEBUG_DEAD_TRANSACTION;
 module_param_named(debug_mask, binder_debug_mask, uint, 0644);
 
-static char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
+char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
 module_param_named(devices, binder_devices_param, charp, 0444);
 
 static DECLARE_WAIT_QUEUE_HEAD(binder_user_error_wait);
@@ -6131,7 +6131,8 @@ 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/binder_internal.h b/drivers/android/binder_internal.h
index 045b3e42d98b..fe8c745dc8e0 100644
--- a/drivers/android/binder_internal.h
+++ b/drivers/android/binder_internal.h
@@ -37,6 +37,8 @@ struct binder_device {
 
 extern const struct file_operations binder_fops;
 
+extern char *binder_devices_param;
+
 #ifdef CONFIG_ANDROID_BINDERFS
 extern bool is_binderfs_device(const struct inode *inode);
 #else
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index d8307cccbef8..55c5adb87585 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -186,8 +186,7 @@ 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 +466,9 @@ 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 +523,22 @@ 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, ",")) {
+                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,