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SubjectRe: [RFC] [PATCH] [3/3] LSM Stacking: stackable bsdjail (Documentation)
The documentation for the bsdjail LSM.

Signed-off-by: Serge E. Hallyn <>

diff -Nrup linux-2.6.9/Documentation/bsdjail.txt
--- linux-2.6.9/Documentation/bsdjail.txt 1969-12-31 18:00:00.000000000
+++ linux-2.6.9-jail/Documentation/bsdjail.txt 2004-10-20
14:41:28.266075800 -0500
@@ -0,0 +1,135 @@
+BSD Jail Linux Security Module
+Serge E. Hallyn <>
+Used in conjunction with per-process namespaces, this implements
+a subset of the BSD Jail functionality as a Linux LSM. What is
+currently implemented:
+ If a proces is in a jail, it:
+ 2. Cannot mount or umount
+ 3. Cannot send signals outside of jail
+ 4. Cannot ptrace processes outside of jail
+ 5. Cannot create devices
+ 6. Cannot renice processes
+ 7. Cannot load or unload modules
+ 8. Cannot change network settings
+ 9. May be assigned a specific ip address which will be used
+ for all it's socket binds.
+ 10. Cannot see contents of /proc/<pid> entries of processes not in
+ same jail. (We hide their existence for convenience's sake,
+ their existance can still be detected using, for instance,
+ 11. Has no CAP_SYS_RAWIO capability (no ioperm/iopl)
+ 12. May not share IPC resources with processes outside its own jail.
+ 13. May find it's valid network address (if restricted) under
+ /proc/$$/attr/current.
+ If properly locked into its own namespace, processes will not be able
+ to escape to parts of the system's filesystem which were made
+ unavailable (without outside help).
+The security of this module is very much dependent on the security
+of the rest of the system. You must carefully think through your
+use of the system.
+Some examples:
+ 1. If you leave /dev/hda1 in the jail, processes in the
+ jail can access that filesystem (i.e. /sbin/debugfs).
+ 2. If you provide root access within a jail, this can of
+ course be used to setuid binaries in the jail. Combined
+ with an unjailed regular user account, this gives jailed
+ users unjailed root access. (thanks to Brad Spender for
+ pointing this out).
+How to use:
+ 1. Load the bsdjail module if not already loaded or compiled in:
+ modprobe bsdjail
+ 3. (Optional) Set up an ipv4 alias for the jail
+ # /sbin/ifconfig eth0:0
+ # /sbin/route add -host dev eth0:0
+ 3. Execute a shell under a new namespace:
+ exec clone_ns
+ (see
+ 4. If not already done, set up the filesystem for the jail. in our
+ example, we will set it up under /opt.
+ mount /dev/hdc5 /opt
+ mount -t proc proc /opt/proc
+ 5. Make sure there is an empty directory to put the old root in.
+ will just use /opt/mnt
+ mkdir /opt/mnt
+ 6. Pivot the old and new roots:
+ cd /opt
+ /sbin/pivot_root . mnt
+ /usr/sbin/chroot . /bin/sh
+ 7. Unmount the old root
+ umount -l /mnt
+ 6. Give the desired arguments for the jail. If no arguments are
+ necessary, just say:
+ echo lock > /proc/$$/attr/exec
+ To lock the process into an ip alias, say:
+ echo "ip" > /proc/$$/attr/exec
+ 7. Execute a new shell. The shell will be under the new jail, and
+ the private namespace you've been setting up.
+ exec /bin/sh
+ 8. To allow friends/customers/whoever to use this system, you might
+ start some services.
+ sshd
+ 9. Ssh is now running under the jail, so you no longer need the
+ shell:
+ exit
+The new shell runs in a private jail on the filesystem on /dev/hdc5. If
+has been mounted under /dev/hdc5, then a "ps -auxw" under the jailed
+will show only entries for processes started under that jail.
+If a private IP was specified for the jail, then
+ cat /proc/$$/attr/current
+will show the address for the private network device. Other network
+devices will be visible through /sbin/ifconfig -a, but not usable.
+If the reading process is not in a jail, then
+ cat /proc/$$/attr/current
+returns information about the root and ip * for the target process,
+or "Not Jailed" if the target process is not jailed.
+Cat /proc/$$/attr/exec gives a list of the valid keywords to cat into
+/proc/$$/attr/exec when starting a jail.
+Current valid keywords for creating a jail are:
+ lock: specifies the next exec should land us in a jail. (only
+ if you don't want to give any other keywords)
+ ip: IPV4 addr for this jail
+ ip6: IPV6 addr for this jail
+ nrtask: Number of tasks in this jail
+ nice: The nice level for this jail. (maybe should be min/max?)
+ slice: Max timeslice per process
+ data: Max size of DATA segment per process
+ memlock: Max size of memory which can be locked per process

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