How to mount .img file as read-only ext4, but give users read permissions to the whole fs?

Question

I have a system.img android's image file that has ext4 filesystem in it. I mount it as

sudo mount -o ro system.img /mnt

I have two questions:

1. Why do I need root access to mount the image file?

Mounting the image file as user gives me the following error:

mount: /mnt: mount failed: Permission denied.

The user has full access to the system.img as it is the owner of file:

ls -l system.img
-rwxr-xr-x 1 user users 4877225984 Apr 12 19:13 system.img

The user doesn't have permission to mount the image file even if the user is the owner of the the directory to which I try to mount the image, like that:

$ mkdir system_mount
$ mount -o ro system.img system_mount
mount: system_mount: mount failed: Permission denied.
$ ls -l
drwxr-xr-x 2 user users       4096 Apr 12 19:38  system_mount 

So why mounting always requires root access?

2. When mounted, the user still may not have access to some directories/files in the mounted filesystem if in the filesystem itself the permissions are not given to the user.

Access to some directories is not permitted, like init.container.rc file (others have no permissions):

-rwxr-x---  1 root 2000  3583 Dec 31  2008 init.container.rc

Trying to get contents of that file fails:

$ cat /mnt/init.container.rc
cat: /mnt/init.container.rc: Permission denied

I still can access that directory as root. And I could access it as user if I used chmod -R 755 if the system was mounted as writable. But as it's not, I get the following kind of errors when I use chmod command:

chmod: changing permissions of '/mnt/d/tracing': Read-only file system

I want to give the user temporary read permissions to the whole filesystem WITHOUT modifying the system.img file (having it mounted as read-only), without actually changing the permissions in the filesystem.

How can I do that?

Answer 1

Kamil Maciorowski's solution, to use fuse2fs.