[PATCH] samples/landlock: Document best-effort approach for LANDLOCK_ACCESS_FS_REFER

[Günther Noack]

On Thu, Nov 03, 2022 at 03:21:32PM +0100, Mickaël Salaün wrote:
> On 30/10/2022 07:11, Günther Noack wrote:
> > Add a comment to clarify how to handle best-effort backwards
> > compatibility for LANDLOCK_ACCESS_FS_REFER.
> > 
> > The "refer" access is special because these operations are always
> > forbidden in ABI 1, unlike most other operations, which are permitted
> > when using Landlock ABI levels where they are not supported yet.
> > 
> > Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
> > ---
> >   samples/landlock/sandboxer.c | 16 +++++++++++++++-
> >   1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> > index fd4237c64fb2..901acb383124 100644
> > --- a/samples/landlock/sandboxer.c
> > +++ b/samples/landlock/sandboxer.c
> > @@ -234,7 +234,21 @@ int main(const int argc, char *const argv[], char *const *const envp)
> > +		 * If only ABI 1 is available, the sample tool knowingly forbids
> 
> s/the sample tool/this sandboxer/
> 
> > +		 * refer operations.
> > +		 *
> > +		 * If a program *needs* to do refer operations after enabling
> > +		 * Landlock, it can not use Landlock at ABI level 1.  To be
> > +		 * compatible across different kernels, such programs should
> > +		 * fall back to not using Landlock instead.
> 
> To be compatible with different kernel versions, such programs should then
> fall back to not restrict themselves at all if the running kernel only
> supports ABI 1.

Thanks for the review, Mickaël! Both suggestions applied, and sent V2.

—Günther

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