On Wed, Jun 23, 2021 at 04:27:47PM +0000, David Laight wrote: > From: Kees Cook > > Sent: 23 June 2021 17:19 > > > > On Wed, Jun 23, 2021 at 01:43:04PM +0000, David Laight wrote: > > > From: Guillaume Tucker > > > > Sent: 23 June 2021 13:40 > > > ... > > > > > diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh > > > > > index bb7a1775307b..0f9f22ac004b 100755 > > > > > --- a/tools/testing/selftests/lkdtm/run.sh > > > > > +++ b/tools/testing/selftests/lkdtm/run.sh > > > > > @@ -78,8 +78,9 @@ dmesg > "$DMESG" > > > > > > > > > > # Most shells yell about signals and we're expecting the "cat" process > > > > > # to usually be killed by the kernel. So we have to run it in a sub-shell > > > > > -# and silence errors. > > > > > -($SHELL -c 'cat <(echo '"$test"') >'"$TRIGGER" 2>/dev/null) || true > > > > > +# to avoid terminating this script. Leave stderr alone, just in case > > > > > +# something _else_ happens. > > > > > +(/bin/sh -c '(echo '"$test"') | cat >'"$TRIGGER") || true > > > > > > I was having trouble parsing that command - and I'm good > > > at shell scripts. > > > I think the extra subshell the 'echo' is in doesn't help. > > > In fact, is either subshell needed? > > > Surely: > > > /bin/sh -c "echo '$test' | cat >$trigger" || true > > > will work just as well? > > > > Ah yeah, and I just tested it to double check, it can be even simpler: > > > > echo "$test" | /bin/sh -c "cat >$TRIGGER" || true > > You can probably even do: > > echo "$test" | /bin/sh -c cat >$TRIGGER || true > > (moving the redirect to the outer shell). Actually, it looks like the "write" is already happening in the exec'd process, so this can just be: echo "$test" | cat >$TRIGGER || true But it still can't be: echo "$test" >$TRIGGER which is what I had over-engineered a solution to. :) -- Kees Cook
