On Mon, 11 Oct 2021 10:47:04 +0200 Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > On 10/10/2021 23:48, Andrew Morton wrote: > > On Fri, 8 Oct 2021 12:48:37 +0200 Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > > >> The final goal of this patch series is to enable the kernel to be a > >> global policy manager by entrusting processes with access control at > >> their level. To reach this goal, two complementary parts are required: > >> * user space needs to be able to know if it can trust some file > >> descriptor content for a specific usage; > >> * and the kernel needs to make available some part of the policy > >> configured by the system administrator. > > > > Apologies if I missed this... > > > > It would be nice to see a description of the proposed syscall interface > > in these changelogs! Then a few questions I have will be answered... > > I described this syscall and it's semantic in the first patch in > Documentation/admin-guide/sysctl/fs.rst Well, kinda. It didn't explain why the `usage' and `flags' arguments exist and what are the plans for them. > Do you want me to copy-paste this content in the cover letter? That would be best please. It's basically the most important thing when reviewing the implementation. > > > > long trusted_for(const int fd, > > const enum trusted_for_usage usage, > > const u32 flags) > > > > - `usage' must be equal to TRUSTED_FOR_EXECUTION, so why does it > > exist? Some future modes are planned? Please expand on this. > > Indeed, the current use case is to check if the kernel would allow > execution of a file. But as Florian pointed out, we may want to add more > context in the future, e.g. to enforce signature verification, to check > if this is a legitimate (system) library, to check if the file is > allowed to be used as (trusted) configuration… > > > > > - `flags' is unused (must be zero). So why does it exist? What are > > the plans here? > > This is mostly to follow syscall good practices for extensibility. It > could be used in combination with the usage argument (which defines the > user space semantic), e.g. to check for extra properties such as > cryptographic or integrity requirements, origin of the file… > > > > > - what values does the syscall return and what do they mean? > > > > It returns 0 on success, or -EACCES if the kernel policy denies the > specified usage. And please document all of this in the changelog also.
