linux-kernel - Re: [PATCH v1 1/2] io_uring,audit: audit IORING_OP_FADVISE but not IORING_OP

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Message-ID: <CAHC9VhSZNGs+SQU7WCD+ObMcwv-=1ZkBts8oHn40qWsQ=n0pXA@mail.gmail.com>
Date:   Fri, 27 Jan 2023 17:35:52 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, io-uring@...r.kernel.org,
        Eric Paris <eparis@...isplace.org>,
        Steve Grubb <sgrubb@...hat.com>, Stefan Roesch <shr@...com>,
        Christian Brauner <brauner@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH v1 1/2] io_uring,audit: audit IORING_OP_FADVISE but not IORING_OP_MADVISE

On Fri, Jan 27, 2023 at 12:24 PM Richard Guy Briggs <rgb@...hat.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@...hat.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?

>         [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.

-- 
paul-moore.com