Date:   Fri, 27 Jan 2023 18:02:44 -0500
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Paul Moore <paul@paul-moore.com>,
        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>,
        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: <Y9RYFHucRL5TrsDh@madcap2.tricolour.ca>
References: <cover.1674682056.git.rgb@redhat.com>
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 <CAHC9VhSZNGs+SQU7WCD+ObMcwv-=1ZkBts8oHn40qWsQ=n0pXA@mail.gmail.com>
 <6d3f76ae-9f86-a96e-d540-cfd45475e288@kernel.dk>
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On 2023-01-27 15:45, Jens Axboe wrote:
> On 1/27/23 3:35?PM, 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?
> 
> Yeah, honestly not sure where that came from. Maybe it's being mixed up
> with fallocate? All fadvise (or madvise, for that matter) does is
> provide hints on the caching or access pattern. On second thought, both
> of these should be able to set audit_skip as far as I can tell.

That was one suspicion I had.  If this is the case, I'd agree both could
be skipped.

> Jens Axboe

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
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