Overview of security and memory management?

edit

A few answers:

A new copy of Sage is started up for each worksheet process. Code to be executed is copied to a temporary directory and can be executed as a very non-privileged user (using the server_pool option in starting up the notebook). Standard OS ulimit functions can be used to limit memory or other resources per worksheet.

You might look at http://wiki.sagemath.org/SageServer for one set of instructions about deploying Sage. Also look in the documentation for the notebook() command for other security options.

sagenb.org has strange permissions at least in /tmp

In a notebook on sagenb.org:

os.system("id")
uid=1168(sagenbws) gid=1168(sagenbws) groups=1168(sagenbws)
os.system("cat /tmp/tmpzxlnwt/___code___.py") #someone's code
os.system("find /tmp type -type f -user sagenbws   -ls 2>/dev/null") #sagenbws is us
1615059    4 -rw-r--r--   1 sagenbws sagenbws      568 Dec  5 13:32 /tmp/tmp0uWxta/___code___.py
 ...
WARNING: Output truncated!

Since system commands are supported one can use the notebook as a proxy or send email.

If one starts the notebook from sage via notebook() the user id is the user running sage so anyone who can login to the notebook in this case can execute system commands as the user running sage (by default creating accounts appears disabled to me in this case).