|POV-Ray for Unix version 3.7|
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I/O Restrictions is a feature that was introduced in POV-Ray for Unix 3.5. The purpose of this feature is to attempt to at least partially protect a machine running POV-Ray from having files read or written outside of a given set of directories.
The need for this is related to the fact that the POV-Ray scene language has, over the years, become something more akin to a scripting language combined with a scene-description model. It is now possible to write obfuscated POV-Ray code, and to open, create, read and write arbitrary files anywhere on the target system's hard disk, subject to operating system permission.
The basic idea of I/O Restrictions is to attempt to protect the user from a script that may have been downloaded from an untrusted source, and which may attempt to create or modify files that it should not.
The I/O Restriction facility hooks the file open and creation functions in the core POV-Ray renderer code, and allows the Unix version to allow or deny any particular file operation.
Note: We do not guarantee that the I/O Restriction facility will actually stop anything from happening. There is always the chance that, like almost all software, it could have a bug in it that causes it to malfunction. Therefore, the onus is on the person who chooses to load an INI or scene file into POV-Ray to ensure that it does not do anything that it should not do. Please consider I/O Restrictions just a sometimes-helpful backup for manual checks.
Please read this section in full so that you understand the caveats and conditions of the facility, as some directories are allowed by default.
The I/O Restrictions are configured by two separate configuration files. This can be a system-wide configuration, or a user configuration file located in the following places, on most systems
POV-Ray will always use the most strict version of what is specified; user settings can only make security more strict.
The general syntax of these files is:
;Comment [Section] setting
Warning: If neither of these files exists I/O Restrictions are deactivated!
[File I/O Security] section only contains a single setting which is either
nonemeans that there are no restrictions other than those enforced by the file system.
read-onlymeans that files may be read without restriction.
restrictedmeans that files access is subject to restrictions as specified in the rest of this file. See below for details.
[Shellout Security] section determines whether POV-Ray will be allowed to call scripts.
This section contains a single setting which is either
allowedmeans that shellout will work as specified in the documentation.
forbiddenmeans that shellout will be disabled.
See the section Shell-out to Operating System for more details.
[Permitted Paths] section contains a list of directories which are specifically allowed for either reading or reading and writing. These paths are only used when the setting for
[File I/O Security] is either
[File I/O Security]is set to
read-only, any directory can be used to read in a file, and
read+writeentries must specify which directories are allowed for writing.
[File I/O Security]is set to
restricted, reading and writing is allowed only in the directories given by the
If the directory name contains spaces it has to be quoted or doubly-quoted. There can be spaces before and after the equal sign. Read-only and read/write entries can be specified in any order.
If you want the permissions for a specified directory to also extend to all of its subdirectories wildcards are permitted.
Both relative and absolute paths are permitted, so the dot character can be especially useful. The install directory, typically
/usr/share/povray-3.7, can be specified with
%INSTALLDIR%, the user home directory with
%HOME%. The install directory and its
descendents are typically only writable by root; therefore it does not make sense to have
%INSTALLDIR% in read/write directory paths.
Note: Since user-level permissions are at least as strict as system-level restrictions, any paths specified in the system-wide
povray.conf will also need to be specified in
~/.povray/3.7/povray.conf if this file exists.
[Permitted Paths] read=%INSTALLDIR%
Would permit reading from the directory where the POV-Ray supplementary files are installed.
Note that the installdir location does not relate to where the binary is run from - it relates to the information defined at compile-time. Relative paths are legal as well, and will be resolved only once at load time (but relative to the current directory, not the installdir). For example, a relative path like the following ...
[Permitted Paths] read+write=../output
Would be resolved with relation to the current directory at the time POV-Ray for Unix was started, so if you started povray while in the directory
~/myscenes/newscene, then the above path would be resolved as
~/myscenes/output. Please note that the actual location of the povray binary is not relevent here - it is the current directory that matters, which is typically not that of the program.
Here is a complete example for a
[File I/O Security] ; none ; read-only restricted [Shellout Security] allowed ; forbidden [Permitted Paths] read*=%INSTALLDIR%/include read*=%INSTALLDIR%/scenes read=%INSTALLDIR%/../../etc read+write=. read+write*=/tmp