Re: [PATCH v1 1/2] io_uring,audit: audit IORING_OP_FADVISE but not IORING_OP_MADVISE

[Paul Moore]

On Fri, Jan 27, 2023 at 5:45 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
> On 1/27/23 3:35?PM, Paul Moore wrote:
> > On Fri, Jan 27, 2023 at 12:24 PM Richard Guy Briggs <rgb@xxxxxxxxxx> 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@xxxxxxxxxx>
> >> ---
> >>  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?

That was my thought too when I was looking at it.

> 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.

Agreed on the fadvise side, and probably the madvise side too,
although the latter has more options/code to sift through so I'm
curious to hear what analysis Richard has done on that one.

-- 
paul-moore.com