File Permissions

Action	---	r--	-w-	--x	rw-	r-x	-wx	rwx	r-s
read - cat file	no	yes	no	no	yes	yes	no	yes
write - ls /tmp >> file	no	no	yes	no	yes	no	yes	yes
write - ls /tmp > file	no	no	yes	no	yes	no	yes	yes
remove file	yes*	yes*	yes	yes*	yes	yes*	yes	yes
executing a script	no	no	no	no	no	yes	no	yes	yes**

yes*: These files gave a "rm: remove write-protected file 'filename'?" error. Saying "yes" removes these files. Also performing a "rm -rf" file removes the file without any warning. The ability to remove a file is controlled at the directory level.
yes**: execute a file with permission of owner or group

Directory Permissions

Action	---	r--	-w-	--x	rw-	r-x	-wx	rwx
cd into directory	no	no	no	yes	no	yes	yes	yes
ls directory	no	yes*	no	no	yes*	yes	no	yes
file name completion	no	yes	no	no	yes	yes	no	yes
create new file in dir.	no	no	no	no	no	no	yes	yes
read file in dir.	no	no	no	yes	no	yes	yes	yes
modify file in dir.	no	no	no	yes	no	yes	yes	yes
remove files	no	no	no	no	no	no	yes	yes
execute script	no	no	no	yes	no	yes	yes	yes

ls = yes* - Only the files are listed with error. No other file attributes are able to be listed. File name completion works in these cases as well.

t - Save text attribute (sticky bit): The user may delete or modify only those files in the directory that they own or have write permission for (/tmp).

s - Set group ID: files in that directory will have the group ownership as the directory, instead of than the group of the user that created the file

If you want to have full access to a directory with 2 different users in different groups make a new group and add both users.

addgroup newgroup
adduser user1 newgroup
adduser user2 newgroup

chown root:newgroup /directory
chmod 775 /directory

You do not need to use group ID (s-Flag).

You can use these commands to set 755 on directories and 644 on files

find -type f -exec chmod 644 {} \;
find -type d -exec chmod 755 {} \;

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scponly

Thursday, June 21, 2007, 11:56 - Network, Security
Posted by Administrator

apt-get install scponly

gunzip /usr/share/doc/scponly/setup_chroot/setup_chroot.sh.gz
chmod 755 /usr/share/doc/scponly/setup_chroot/setup_chroot.sh
cd /usr/share/doc/scponly/setup_chroot/
./setup_chroot.sh /home/USERNAME USERNAME RELATIVE_WRITEABLE_DIR

cp /dev/null /home/USERNAME/dev

maybe cp /etc/groups /home/USERNAME/etc

HINT: login via ssh is not possible BUT PORTFORWARDING

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ssh - chroot

Thursday, June 21, 2007, 10:36 - Network, Security
Posted by Administrator

chroot a user logging in via ssh

apt-get install libpam-chroot

less /usr/share/doc/libpam-chroot/examples/README.example

/usr/share/doc/libpam-chroot/examples/setup-chrootdir-shell.sh

/etc/security/chroot.conf:

+USERNAME   /var/chroot/sshd/home/USERNAME

/etc/pam.d/login:

+session    required   pam_chroot.so

To copy all linked libs (but not libs loaded at runtime) of a programm to our chroot

ldd /usr/bin/pprogram | awk '{if ($3 ~ /^[^ (]/) print $3}' | \
cpio -pdvuL $CHROOTDIR

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