mjhjmtu

I am concerned about the possibility that a normal user can delete important files from like /etc/passwd or files from /boot. They can do it because the permissions on /etc and /boot are drwxr-xr-x.
Should I worry about this or am I missing something?

Thank you

No. The permissions that you see can be split into four components: type of entry, owner permissions, group permissions, and "all" permissions; "all" simply refers to anyone who is neither the owner or a member of the group. What the permissions mean depend on whether the entry is a file or a directory. A more thorough description of how permissions work is here.

So, for this example:

$ ls -dl /etc /etc/passwd /etc/shadow
drwxr-xr-x 58 root root 4096 Feb 13 19:08 /etc
-rw-r--r-- 1 root root 1887 Oct 11 21:49 /etc/passwd
-rw-r----- 1 root root 970 Oct 11 21:49 /etc/shadow

For /etc:

• 
  d: the entry is a directory.


• 
  rwx: the owner of the directory (root) has full permissions to view and modify (add/delete/rename) file entries, and change to ("cd") this directory.


• 
  r-x: members of the group (also called root, but is not the same as the user called root) have permissions to view file entries and change to ("cd") this directory.


• 
  r-x: everyone else has permissions to view file entries and change to ("cd") this directory.

Note that having permission to read a directory does not mean that you can read the contents of individual files: that is what file permissions are for.

Individual files work in a similar way, but the permissions refer to reading, writing and executing the file itself.

For /etc/passwd:

• 
  -: the entry is a regular file.


• 
  rw-: the owner (root) can read and write to this file, but not run it directly from the command line.


• 
  r--: members of the group (root) can only read this file.


• 
  r--: everyone else can read this file.

Originally the /etc/passwd file did have (encrypted) passwords in it, but that was judged to be a security risk so the passwords were moved to a "shadow" copy of the password file called /etc/shadow. It is only accessible by the root user and group (-rw-r-----): regular users cannot view it.

The owner of /etc and /boot is or should be root.

echo test > /etc/test 
bash: /etc/test: Permission denied

Only the owner root has the permission to create files or delete them from the directory.

To delete a file a user needs write permission on the parent directory of the file. With the permissions set to drwxr-xr-x only the owner of those directorys can delete files in them