[Cc'ing Casey] On Tue, 2020-09-08 at 16:14 +0200, Mickaël Salaün wrote: > On 08/09/2020 15:42, Stephen Smalley wrote: > > On Tue, Sep 8, 2020 at 9:29 AM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > >> > >> On Tue, 2020-09-08 at 08:52 -0400, Stephen Smalley wrote: > >>> On Tue, Sep 8, 2020 at 8:50 AM Stephen Smalley > >>> <stephen.smalley.work@xxxxxxxxx> wrote: > >>>> > >>>> On Tue, Sep 8, 2020 at 8:43 AM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > >>>>> > >>>>> > >>>>> On 08/09/2020 14:28, Mimi Zohar wrote: > >>>>>> Hi Mickael, > >>>>>> > >>>>>> On Tue, 2020-09-08 at 09:59 +0200, Mickaël Salaün wrote: > >>>>>>> + 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. > >> > >>>> > >>>> 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? > > > > selinux_inode_permission() has special handling for MAY_ACCESS so we'd > > need to duplicate that into selinux_file_permission() -> > > selinux_revalidate_file_permission(). Also likely need to adjust > > selinux_file_permission() to explicitly check whether the mask > > includes any permissions not checked at open time. So some changes > > would be needed here. By default, it would be a no-op unless there > > was a policy reload or the file was relabeled between the open(2) and > > the faccessat(2) call. > > > > We could create a new hook path_permission(struct path *path, int mask) > as a superset of inode_permission(). To be more convenient, his new hook > could then just call inode_permission() for every LSMs not implementing > path_permission(). The LSM maintainers need to chime in here on this suggestion. In terms of the name, except for one hook, all the security_path_XXXX() hooks are dependent on CONFIG_SECURITY_PATH being configured. Mimi
