From: "Günther Noack" <gnoack3000@gmail.com>
To: Alejandro Colomar <alx.manpages@gmail.com>
Cc: "Mickaël Salaün" <mic@digikod.net>, linux-man@vger.kernel.org
Subject: Re: [PATCH v6 1/1] landlock.7: Explain the best-effort fallback mechanism in the example
Date: Sat, 15 Apr 2023 09:16:50 +0200 [thread overview]
Message-ID: <20230415.de079bcd1e29@gnoack.org> (raw)
In-Reply-To: <ba15e85d-db90-88cf-ca60-1d4a11a40c31@gmail.com>
Hello Alejandro!
On Fri, Apr 14, 2023 at 06:35:22PM +0200, Alejandro Colomar wrote:
> On 4/14/23 17:59, Günther Noack wrote:
> > Signed-off-by: Günther Noack <gnoack3000@gmail.com>
> > ---
> > man7/landlock.7 | 70 ++++++++++++++++++++++++++++++++++++++++++++++---
> > 1 file changed, 66 insertions(+), 4 deletions(-)
> >
> > diff --git a/man7/landlock.7 b/man7/landlock.7
> > index 24488465e..64bfa0752 100644
> > --- a/man7/landlock.7
> > +++ b/man7/landlock.7
> > [...]
> > +/*
> > + * Table of available file system access rights by ABI version,
> > + * numbers hardcoded to keep the example short.
> > + */
> > +__u64 landlock_fs_access_rights[] = {
> > + (1ULL << 13) \- 1, /* ABI v1 */
> > + (1ULL << 14) \- 1, /* ABI v2: add "refer" */
> > + (1ULL << 15) \- 1, /* ABI v3: add "truncate" */
> > +};
> > +
> > +int abi = landlock_create_ruleset(NULL, 0,
> > + LANDLOCK_CREATE_RULESET_VERSION);
> > +if (abi <= 0) {
> > + perror("Giving up \- No Landlock support");
>
> Using perror(3) will already print "Operation not supported", since
> errno is ENOTSUP. Maybe this string is redundant? How about the
> following?
>
> perror("landlock_create_ruleset"); // EOPNOTSUPP
The fallback code assumes that we don't know the kernel that we run on,
so in practice we also have to handle ENOSYS.
See https://docs.kernel.org/userspace-api/landlock.html#landlock-abi-versions
I'd suggest to just make it more explicit here that it can be two
different error codes:
if (abi <= 0) {
/* ENOTSUP or ENOSYS */
perror("Giving up \- No Landlock support");
}
Does that sound reasonable?
> BTW, now I checked that while in Linux ENOTSUP and EOPNOTSUPP are
> equivalent, in POSIX the latter has a connotation that it's about
> sockets. Should we document ENOTSUP in landlock_create_ruleset(2)
> instead of EOPNOTSUPP?
EOPNOTSUP is also used in Landlock's kernel documentation,
we'd maybe have to update it there as well.
I'll have a look at what is more common.
> > + exit(EXIT_FAILURE);
> > +}
> > +if (abi > 3)
> > + abi = 3;
>
> This makes the example a line shorter (see MIN(3)):
>
> abi = MIN(abi, 3);
Thanks, good point! I'll add that.
–Günther
next prev parent reply other threads:[~2023-04-15 7:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-14 15:59 [PATCH v6 0/1] landlock.7: Explain best-effort fallback in example Günther Noack
2023-04-14 15:59 ` [PATCH v6 1/1] landlock.7: Explain the best-effort fallback mechanism in the example Günther Noack
2023-04-14 16:35 ` Alejandro Colomar
2023-04-15 7:16 ` Günther Noack [this message]
2023-04-17 17:24 ` Alejandro Colomar
2023-04-17 20:54 ` Mickaël Salaün
2023-04-18 14:37 ` Alejandro Colomar
2023-04-18 20:50 ` Mickaël Salaün
2023-04-18 20:54 ` Alejandro Colomar
2023-04-18 20:55 ` Alejandro Colomar
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