PHP mkdir permission denied in Docker conatiner - php

Question

I've read a few questions about the same problem but i couldn't find any answer that works. I have a "mkdir permission denied" problem in PHP. I've tryed to change a few directories and users permissions, but it still doesn't work.
So, the erro is: "Warning: mkdir(): Permission denied in /www/denunciar/private/utilits.php on line 52"
This is my Docker-compose yml file:
services:
webserver:
image: nginx:stable
container_name: nginx
restart: always
ports:
- 80:80
volumes:
- ./www:/www
- ./site.conf:/etc/nginx/conf.d/site.conf
links:
- php
php:
image: php:8-fpm
container_name: php-fpm
volumes:
- ./www:/www
links:
- mysql-db-gestaofisc
mysql-db-gestaofisc:
image: mysql:5.7
container_name: mysql
ports:
- "3306:3306"
command: --default-authentication-plugin=mysql_native_password
restart: always
environment:
MYSQL_ROOT_PASSWORD: *****
MYSQL_DATABASE: dbname
MYSQL_USER: uname
MYSQL_PASSWORD: *****
links:
- phpmyadmin
phpmyadmin:
image: phpmyadmin/phpmyadmin
ports:
- "8084:80"
restart: always
environment:
PMA_HOST: mysql-db-gestaofisc
In the Nginx container, i set root group and root user as www directory's owner and nginx user in root group:
# pwd
/
# ls -la
total 88
drwxr-xr-x 1 root root 4096 Aug 9 19:10 .
drwxr-xr-x 1 root root 4096 Aug 9 19:10 ..
-rwxr-xr-x 1 root root 0 Aug 9 19:10 .dockerenv
drwxr-xr-x 2 root root 4096 Aug 1 00:00 bin
drwxr-xr-x 2 root root 4096 Jun 30 21:35 boot
drwxr-xr-x 5 root root 340 Aug 11 16:45 dev
drwxr-xr-x 1 root root 4096 Aug 2 05:18 docker-entrypoint.d
-rwxrwxr-x 1 root root 1202 Aug 2 05:17 docker-entrypoint.sh
drwxr-xr-x 1 root root 4096 Aug 9 19:47 etc
drwxr-xr-x 2 root root 4096 Jun 30 21:35 home
drwxr-xr-x 1 root root 4096 Aug 1 00:00 lib
drwxr-xr-x 2 root root 4096 Aug 1 00:00 lib64
drwxr-xr-x 2 root root 4096 Aug 1 00:00 media
drwxr-xr-x 2 root root 4096 Aug 1 00:00 mnt
drwxr-xr-x 2 root root 4096 Aug 1 00:00 opt
dr-xr-xr-x 357 root root 0 Aug 11 16:45 proc
drwx------ 2 root root 4096 Aug 1 00:00 root
drwxr-xr-x 1 root root 4096 Aug 11 16:45 run
drwxr-xr-x 2 root root 4096 Aug 1 00:00 sbin
drwxr-xr-x 2 root root 4096 Aug 1 00:00 srv
dr-xr-xr-x 11 root root 0 Aug 11 16:45 sys
drwxrwxrwt 1 root root 4096 Aug 2 05:18 tmp
drwxr-xr-x 1 root root 4096 Aug 1 00:00 usr
drwxr-xr-x 1 root root 4096 Aug 1 00:00 var
drwxrwxrwx 1 root root 512 Aug 9 19:27 www
# groups nginx
nginx : nginx root
#
Also, in PHP container i did the same with www directory and www-data user:
# pwd
/
# ls -la
total 80
drwxr-xr-x 1 root root 4096 Aug 9 19:10 .
drwxr-xr-x 1 root root 4096 Aug 9 19:10 ..
-rwxr-xr-x 1 root root 0 Aug 9 19:10 .dockerenv
drwxr-xr-x 1 root root 4096 Aug 2 06:17 bin
drwxr-xr-x 2 root root 4096 Jun 30 21:35 boot
drwxr-xr-x 5 root root 340 Aug 11 16:45 dev
drwxr-xr-x 1 root root 4096 Aug 11 16:42 etc
drwxr-xr-x 2 root root 4096 Jun 30 21:35 home
drwxr-xr-x 1 root root 4096 Aug 2 06:17 lib
drwxr-xr-x 2 root root 4096 Aug 1 00:00 lib64
drwxr-xr-x 2 root root 4096 Aug 1 00:00 media
drwxr-xr-x 2 root root 4096 Aug 1 00:00 mnt
drwxr-xr-x 2 root root 4096 Aug 1 00:00 opt
dr-xr-xr-x 358 root root 0 Aug 11 16:45 proc
drwx------ 1 root root 4096 Aug 4 21:10 root
drwxr-xr-x 3 root root 4096 Aug 1 00:00 run
drwxr-xr-x 2 root root 4096 Aug 1 00:00 sbin
drwxr-xr-x 2 root root 4096 Aug 1 00:00 srv
dr-xr-xr-x 11 root root 0 Aug 11 16:45 sys
drwxrwxrwt 1 root root 4096 Aug 11 16:49 tmp
drwxr-xr-x 1 root root 4096 Aug 1 00:00 usr
drwxr-xr-x 1 root root 4096 Aug 2 06:17 var
drwxrwxrwx 1 root root 512 Aug 9 19:27 www
# groups www-data
www-data : www-data root
#
After that, as both users are in root group, they should have all permissions, don't they ?