Re: [RFC PATCH v8 1/3] fs: Introduce AT_INTERPRETED flag for faccessat2(2)

On Tue, 2020-09-08 at 08:52 -0400, Stephen Smalley wrote:

On Tue, Sep 8, 2020 at 8:50 AM Stephen Smalley
[off-list ref] wrote:

quoted

On Tue, Sep 8, 2020 at 8:43 AM Mickaël Salaün [off-list ref] wrote:

quoted

On 08/09/2020 14:28, Mimi Zohar wrote:

quoted

Hi Mickael,

On Tue, 2020-09-08 at 09:59 +0200, Mickaël Salaün wrote:

quoted

+                    mode |= MAY_INTERPRETED_EXEC;
+                    /*
+                     * For compatibility reasons, if the system-wide policy
+                     * doesn't enforce file permission checks, then
+                     * replaces the execute permission request with a read
+                     * permission request.
+                     */
+                    mode &= ~MAY_EXEC;
+                    /* To be executed *by* user space, files must be readable. */
+                    mode |= MAY_READ;

After this change, I'm wondering if it makes sense to add a call to
security_file_permission().  IMA doesn't currently define it, but
could.

Yes, that's the idea. We could replace the following inode_permission()
with file_permission(). I'm not sure how this will impact other LSMs though.

I wasn't suggesting replacing the existing security_inode_permission
hook later, but adding a new security_file_permission hook here.

quoted

They are not equivalent at least as far as SELinux is concerned.
security_file_permission() was only to be used to revalidate
read/write permissions previously checked at file open to support
policy changes and file or process label changes.  We'd have to modify
the SELinux hook if we wanted to have it check execute access even if
nothing has changed since open time.

Also Smack doesn't appear to implement file_permission at all, so it
would skip Smack checking.

My question is whether adding a new security_file_permission call here
would break either SELinux or Apparmor?

Mimi