Linux directory read and execute bits

file pippo.txt is in /vagrant/one/two, and it belongs to root, just like directories one and two.

[root@osb-vagrant vagrant]# ls -Rlt /vagrant
/vagrant:
total 4
drwxr-xr-x 3 root root 4096 Oct 26 08:29 one

/vagrant/one:
total 4
drwxr-x--x 2 root root 4096 Oct 26 08:29 two

/vagrant/one/two:
total 0
-rw-r--r-- 1 root root 0 Oct 26 08:29 pippo.txt

Question: will user vagrant be able to do ls /vagrant/one/two?
Answer: NO

[vagrant@osb-vagrant vagrant]$ ls /vagrant/one/two/
ls: cannot open directory /vagrant/one/two/: Permission denied

Why not? Because the "two" read bit is not set. It is set on "one" however". The "read" bit for a folder means "let me list its content". However, user vagrant can "cat /vagrant/one/two/pippo.txt", because the read bit is set on pippo.txt, and the execute bit is set on "two".
If I remove the execute bit on "two":

chmod 770 /vagrant/one/two
ls -ltr /vagrant/one/two
total 0
-rw-r--r-- 1 root root 0 Oct 26 08:29 pippo.txt

then I even lose the right to view pippo.txt content, although the file itself is readable for vagrant.

[vagrant@osb-vagrant vagrant]$ cat /vagrant/one/two/pippo.txt
cat: /vagrant/one/two/pippo.txt: Permission denied

To recap: execute bit on a folder allows me to "traverse it". read bit on a folder allows me to view its content. This is very un-intuitive and derives from an overloaded use of bits which were originally meant for files. Files and directories are totally different beasts, so they should be modeled differently.

How about deleting files? It's not enough that you have "write" access to the file: you should also have execute access to the folder.

See also these excellent tutorials http://www.hackinglinuxexposed.com/articles/20030417.html http://www.hackinglinuxexposed.com/articles/20030424.html