linux-ext4 - Does the filesystem alter file permissions?

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Date:	Fri, 10 Oct 2014 15:41:41 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Theodore Ts'o <tytso@....edu>
cc:	linux-ext4@...r.kernel.org
Subject: Does the filesystem alter file permissions?

I'm getting very weird results when creating new files on ext4 
filesystems (this is on a CentOS 7 system).  The permissions are not 
what they should be.

On the / filesystem, as superuser:

[root@...ver ~]# umask
0000
[root@...ver ~]# touch a
[root@...ver ~]# ls -l a
-r--r----- 1 root root 0 Oct 10 11:45 a

As a normal user:

[stern@...ver ~]$ umask
0000
[stern@...ver ~]$ touch b
[stern@...ver ~]$ ls -l b
-rw------- 1 stern stern 0 Oct 10 11:47 b

In /boot (which is a separate ext4 filesystem):

[root@...ver boot]# umask
0000
[root@...ver boot]# touch a
[root@...ver boot]# ls -l a
-r--r--r--. 1 root root 0 Oct 10 15:30 a

On a tmpfs filesystem, the permissions are -rw-rw-rw-, as expected.

What causes this sort of thing, and how can I change it?

Thanks,

Alan Stern

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