Re: [PATCH 1/1] s390/dasd: fix string length handling

[Nick Desaulniers]

On Tue, Aug 29, 2023 at 1:02 AM Heiko Carstens <hca@xxxxxxxxxxxxx> wrote:
>
> On Mon, Aug 28, 2023 at 03:46:52PM -0700, Nick Desaulniers wrote:
> > On Mon, Aug 28, 2023 at 05:31:42PM +0200, Heiko Carstens wrote:
> > > Building dasd_eckd.o with latest clang reveals this bug:
> > >
> > >     CC      drivers/s390/block/dasd_eckd.o
> > >       drivers/s390/block/dasd_eckd.c:1082:3: warning: 'snprintf' will always be truncated;
> > >       specified size is 1, but format string expands to at least 11 [-Wfortify-source]
> > >        1082 |                 snprintf(print_uid, sizeof(*print_uid),
> > >             |                 ^
> > >       drivers/s390/block/dasd_eckd.c:1087:3: warning: 'snprintf' will always be truncated;
> > >       specified size is 1, but format string expands to at least 10 [-Wfortify-source]
> > >        1087 |                 snprintf(print_uid, sizeof(*print_uid),
> > >             |                 ^
> > >
> > > Fix this by moving and using the existing UID_STRLEN for the arrays
> > > that are being written to. Also rename UID_STRLEN to DASD_UID_STRLEN
> > > to clarify its scope.
> > >
> > > Fixes: 23596961b437 ("s390/dasd: split up dasd_eckd_read_conf")
> > > Reviewed-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
> > > Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
> >
> > Thanks for the patch! Nathan just reported a bunch of these. I took a
> > look at these two and thought "yeah that's clearly a bug in the kernel
> > sources." Fix LGTM.
> >
> > Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> > Closes: https://github.com/ClangBuiltLinux/linux/issues/1923
> > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> >
> > I also like David's idea of passing `char ident [DASD_UID_STRLEN]`, too,
> > but I don't feel strongly either way.
>
> Well, this is supposed to be the "minimal" fix. I consider everything else
> additional cleanup work, which can and should be done by Stefan and Jan who
> maintain this device driver.

Sure, like I said, I don't care either way.

>
> For example there is more or less identical code within dasd_devmap.c
> (dasd_uid_show()), where it would make sense to de-deduplicate the
> code. And then of course there is the already mentioned rather pointless
> strlen() invocation; plus there are many other string operations / format
> strings, which also should be addressed.
> E.g. there are quite a couple of "%p" printk format specifiers which are
> pointless, since pointer values get hashed since years - so a more or less
> random value will be printed, etc.

kptr_restrict can be disabled at runtime though, so it's not useless
to print pointer values (IMO).

>
> However all of this is up to Stefan and Jan.
>
> So I consider this current fix as good enough and final.

Thanks for the patch.

-- 
Thanks,
~Nick Desaulniers