Date:   Fri, 27 Jan 2023 17:55:05 -0500
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, io-uring@vger.kernel.org,
        Eric Paris <eparis@parisplace.org>,
        Steve Grubb <sgrubb@redhat.com>, Stefan Roesch <shr@fb.com>,
        Christian Brauner <brauner@kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>
Subject: Re: [PATCH v1 1/2] io_uring,audit: audit IORING_OP_FADVISE but not
 IORING_OP_MADVISE
Message-ID: <Y9RWSZJt7NruCPZ+@madcap2.tricolour.ca>
References: <cover.1674682056.git.rgb@redhat.com>
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 <CAHC9VhSZNGs+SQU7WCD+ObMcwv-=1ZkBts8oHn40qWsQ=n0pXA@mail.gmail.com>
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On 2023-01-27 17:35, Paul Moore wrote:
> On Fri, Jan 27, 2023 at 12:24 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> >
> > Since FADVISE can truncate files and MADVISE operates on memory, reverse
> > the audit_skip tags.
> >
> > Fixes: 5bd2182d58e9 ("audit,io_uring,io-wq: add some basic audit support to io_uring")
> > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > ---
> >  io_uring/opdef.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/io_uring/opdef.c b/io_uring/opdef.c
> > index 3aa0d65c50e3..a2bf53b4a38a 100644
> > --- a/io_uring/opdef.c
> > +++ b/io_uring/opdef.c
> > @@ -306,12 +306,12 @@ const struct io_op_def io_op_defs[] = {
> >         },
> >         [IORING_OP_FADVISE] = {
> >                 .needs_file             = 1,
> > -               .audit_skip             = 1,
> >                 .name                   = "FADVISE",
> >                 .prep                   = io_fadvise_prep,
> >                 .issue                  = io_fadvise,
> >         },
> 
> I've never used posix_fadvise() or the associated fadvise64*()
> syscalls, but from quickly reading the manpages and the
> generic_fadvise() function in the kernel I'm missing where the fadvise
> family of functions could be used to truncate a file, can you show me
> where this happens?  The closest I can see is the manipulation of the
> page cache, but that shouldn't actually modify the file ... right?

I don't know.  I was going on the advice of Steve Grubb.  I'm looking
for feedback, validation, correction, here.

> >         [IORING_OP_MADVISE] = {
> > +               .audit_skip             = 1,
> >                 .name                   = "MADVISE",
> >                 .prep                   = io_madvise_prep,
> >                 .issue                  = io_madvise,
> 
> I *think* this should be okay, what testing/verification have you done
> on this?  One of the things I like to check is to see if any LSMs
> might perform an access check and/or generate an audit record on an
> operation, if there is a case where that could happen we should setup
> audit properly.  I did a very quick check of do_madvise() and nothing
> jumped out at me, but I would be interested in knowing what testing or
> verification you did here.

No testing other than build/boot/audit-testsuite.  You had a test you
had developed that went through several iterations?

> paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635