Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg

[Joe Lawrence]

On 9/9/20 3:49 PM, Kees Cook wrote:
> On Fri, Jun 26, 2020 at 01:59:43PM -0700, Kees Cook wrote:
> > Instead of full GNU diff (which smaller boot environments may not have),
> > use "comm" which is more available.
> >
> > Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> > Link: https://lore.kernel.org/lkml/CA+G9fYtHP+Gg+BrR_GkBMxu2oOi-_e9pATtpb6TVRswv1G1r1Q@xxxxxxxxxxxxxx
> > Fixes: f131d9edc29d ("selftests/lkdtm: Don't clear dmesg when running tests")
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> Shuah, this really needs to land to fix lkdtm tests on busybox. Can
> you add this to -next? (Or is it better to direct this to Greg for the
> lkdtm tree?)
>
> Thanks!
>
> -Kees
>
> > ---
> >   tools/testing/selftests/lkdtm/run.sh | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
> > index 8383eb89d88a..5fe23009ae13 100755
> > --- a/tools/testing/selftests/lkdtm/run.sh
> > +++ b/tools/testing/selftests/lkdtm/run.sh
> > @@ -82,7 +82,7 @@ dmesg > "$DMESG"
> >   ($SHELL -c 'cat <(echo '"$test"') >'"$TRIGGER" 2>/dev/null) || true
> >   
> >   # Record and dump the results
> > -dmesg | diff --changed-group-format='%>' --unchanged-group-format='' "$DMESG" - > "$LOG" || true
> > +dmesg | comm -13 "$DMESG" - > "$LOG" || true
> >   
> >   cat "$LOG"
> >   # Check for expected output
> > --
> > 2.25.1
> >
> >
> > --
> > Kees Cook

Hi Kees,

You may want to consider a similar follow up to the one Miroslav made to 
the livepatching equivalent:

https://lore.kernel.org/live-patching/nycvar.YFH.7.76.2008271528000.27422@xxxxxxxxxxxxx/T/#m1c17812d2c005dd57e9a299a4a492026a156619e

basically 'comm' will complain if two lines from dmesg have the same 
timestamp prefix and their text portions are not sorted.

Regards,

-- Joe