On Tue, 2004-11-09 at 16:05, Stephen Smalley wrote:
> Sorry, the last statement isn't accurate; this patch only provides
> SELinux policy control over the ability to have a mapping that is
> simultaneously writable and executable. One could still create a rw
> mapping and then later change its protection to rx. For anonymous
> mappings, the patch could be trivially modified to apply the check for
> any PROT_EXEC mapping and thus prevent executable anonymous mappings
> entirely except when explicitly allowed; that seems reasonable. Private
> file mappings are more problematic.

Ok, based on feedback and some sample code from Roland McGrath (but any bugs are likely mine), here are revised kernel and policy patches with the following changes:
- permission name has changed from wxpage to execmem to more accurately represent the meaning,
- always check this permission for any executable anonymous mapping, whether presently writable or not,
- check this permission not only for a writable executable private file mapping, but also for an executable private file mapping that has been previously written (based on whether a COW has occurred for the mapping).

This brings the check closer to the goal of controlling the ability to make executable a mapping that can contain data not covered by file permission checks.

Constructive comments welcome.

-- 
Stephen Smalley <sds@epoch.ncsc.mil>
National Security Agency




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