Strange permissions on directory created by mkdir (no execution) - linux

Question

I have this old Perl script. This script is working from cron on CentOS 6.4. It creates a temporary directory and is trying to unzip files there.
This is a piece of code:
$lg->li("Creating Directory... \n\t$unzip_dir");
mkdir ($unzip_dir, 0777) or my_die("mkdir $unzip_dir failed") unless (-e $unzip_dir && -d $unzip_dir);
However after execution the directory has weird permissions:
drwxrwsr-x 42 buser agroup 12K Dec 30 09:18 .
drwxrwsr-x 4 buser agroup 4.0K Apr 6 2012 ..
drw-rwSr-- 2 auser agroup 4.0K Dec 28 11:51 tm_unpack_dir_1388412502.20184
The umask for user auser is a 0002.
Why the new directory has no execution permission? Any idea, how this can happen?

Answer 1

The weird permissions are caused by the setgid bit on the parent directory in combination with an unusual umask:
Look at the permissions of the parent directory, the first line:
drwxrwsr-x 42 buser agroup 12K Dec 30 09:18 .
drw-rwSr-- 2 auser agroup 4.0K Dec 28 11:51 tm_unpack_dir_1388412502.20184
Notice it has rwxrwsr-x which means that the setgid bit is set. The setgid bit on a directory causes new files in the directory to be created with the same group as the directory. New directories inherit the setgid bit from their parent.
A umask of 0113 will cause the strange permissions you're seeing. That is an unusual umask, the default is 0022. The umask is set in the environment executing the script, or directly in the script itself.
Don't worry about 0777 after mkdir in your script: mkdir $dir, 0777 means "create $dir without interfering with the present umask". 0777 is the default and can be safely omitted.
Try setting the umask directly in your script:
umask 0022;
$lg->li("Creating Directory... \n\t$unzip_dir");
mkdir ($unzip_dir) or my_die("mkdir $unzip_dir failed") unless (-e $unzip_dir && -d $unzip_dir);
should cause:
drwxrwsr-x 42 buser agroup 12K Dec 30 09:18 .
drwxr-sr-x 2 auser agroup 4.0K Dec 28 11:51 tm_unpack_dir_1388412502.20184
New directory permissions are rwxr-sr-x which is more normal. Notice that the setgid bit is still set because of the parent directory.
Oh, you might wonder why the setgid bit is sometimes lowercase 's' and sometimes uppercase 'S'. That depends on the executable bit. Lowercase s means the executable bit is set, uppercase means it's not set:
$ mkdir foo
$ ls -l
drwxr-xr-x 2 johan johan 4096 Dec 30 17:22 foo
$ chmod g+s foo
$ ls -l
drwxr-sr-x 2 johan johan 4096 Dec 30 17:22 foo
$ chmod g-x foo
$ ls -l
drwxr-Sr-x 2 johan johan 4096 Dec 30 17:22 foo

Answer 2

Your code looks correct to me.
Confirming on my system:
perl -e 'mkdir("foo", 0777);'
drwxr-xr-x 2 user user 512 Dec 30 10:48 foo
mkdir is affected by your umask. A funky umask can do funky things.
What does this yield for you?
perl -e 'printf("%04o\n", umask());'
I get this:
0022
Which is why my folder is created 0755 when I ask for 0777.

Answer 3

I've debugged script and found source of the problem.
The problem caused by tar.gz archive sent to us by one of our submitters. These tar files having directory without execution permission set. I have no idea how they achieve such result.
One more problem - the Gnu Tar have no key to prevent restoring files and directories permissions.
So after extracting archive with wrong permissions I have to recursively set right permissions on the all files and directories in the archive.
Thank you everybody.

Answer 4

It means that the setuid and setgid bits have been set.
The setuid (set user id) is a permission bit, that allows the users to exec a program with the permissions of its owner.
The setgid (set group id) is a bit that allows the user to exec a program with the permissions of the group owner.
http://linuxg.net/how-to-set-the-setuid-and-setgid-bit-for-files-in-linux-and-unix/