Re: [PATCH 1/2] Makefile: fix _FORTIFY_SOURCE redefined build error

[William Roberts <bill.c.roberts@gmail.com>]

On Wed, Dec 19, 2018 at 1:12 AM Patrick Steinhardt <ps@pks.im> wrote:
>
> Hi,
>
> On Tue, Dec 18, 2018 at 08:03:54AM -0800, William Roberts wrote:
> > Patrick,
> >
> > Hoping you could maybe weigh in on your choice for bypassing the
> > compiler driver with -Wp and not setting _FORTIFY_SOURCE to something
> > like 1 or 2?
> >
> > I'm seeing this issue on Ubuntu 16.04.5:
> > <command-line>:0:0: error: "_FORTIFY_SOURCE" redefined [-Werror]
> >
> > gcc version:
> > gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609
> >
> > My thought is to undef/redef _FORTIFY_SOURCE in CFLAGS and set the
> > level to 2. Setting CFLAGS via the env/make arg will override this
> > behavior
> > and use CFLAGS as is.
>
> I used "-Wp" simply because it was existing previously, so I just
> stuck to what was there already. The original issue I had was
> that Gentoo Hardened, as Jason notes, already defines
> _FORTIFY_SOURCE as part of the compiler spec. Due to that, I was
> seeing a lot of warnings.
>
> So I set the flag to a simple define without setting a specific
> value, which _seemed_ to let the issue go away. But going back to
> the initial issue, this didn't seem to have solved it correctly.
> Dunno what I've been doing back then to not see the warnings
> after my change anymore, but I noticed that they have resurface
> recently.
>
> So I guess the real fix would be to redefine the value by first
> undef'ing it and then redefining it to the desired value. And I
> do agree that in that case, we should simply revert to
> _FORTIFY_SOURCE=2.
>
> Patrick
>
> > On Fri, Dec 14, 2018 at 8:02 AM William Roberts
> > <bill.c.roberts@gmail.com> wrote:
> > >
> > > On Fri, Dec 14, 2018 at 6:32 AM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> > > >
> > > > On 12/14/18 8:43 AM, Stephen Smalley wrote:
> > > > > On 12/13/18 4:32 PM, bill.c.roberts@gmail.com wrote:
> > > > >> From: William Roberts <william.c.roberts@intel.com>
> > > > >>
> > > > >> Certain builds of gcc enable _FORTIFY_SOURCE which results in the error:
> > > > >> <command-line>:0:0: warning: "_FORTIFY_SOURCE" redefined
> > > > >> <command-line>:0:0: note: this is the location of the previous definition
> > > > >>
> > > > >> Correct this by undefining it first and redefining it. Also, the previous
> > > > >> command line option was using -Wp which passing the value *AS IS* to the
> > > > >> pre-processor rather than to the compiler driver. The C pre-processor has
> > > > >> an undocumented interface subject to change per man 1 gcc. Just use the
> > > > >> -D option as is.
> > > > >
> > > > > See commit ca07a2ad46be141dad90d885dd33a2ac31c6559a ("libselinux: avoid
> > > > > redefining _FORTIFY_SOURCE") for why we don't specify a value for
> > > > > _FORTIFY_SOURCE here.  Not sure about the -Wp,-D vs -D rationale.
> > >
> > > I'm not 100% convinced that the patch is the best solution or the commit message
> > > is describing the problem correctly. I could also be understanding it
> > > wrong here.
> > > The man page is saying not to bypass the compiler driver via -Wp, and I don't
> > > see a good reason for it either.
> > >
> > > See my comments below, they feed back into this.
> > >
> > > >
> > > > I guess the issue here is that we want to provide sane defaults for
> > > > building without breaking the build when others specify their own
> > > > definitions and without weakening those definitions.  By undefining and
> > > > re-defining, it seems like we might weaken existing builds that were
> > > > specifying 2.
> > >
> > > We conditionally assign to CFLAGS via ?= operator. Thus, CFLAGS and the
> > > corresponding addition of EXTRA_CFLAGS which contains the undef/def
> > > is not appended. CFLAGS specified via the environment or as an argument to
> > > make will cause this assignment not to occur (via ?= semantics) and whatever
> > > they specify for CFLAGS is sent to CC.
> > >
> > > Here is some sample output:
> > > make CFLAGS='-D_FORTIFY_SOURCE=2'
> > > cc -D_FORTIFY_SOURCE=2 -I../include -D_GNU_SOURCE -DNO_ANDROID_BACKEND
> > >  -fPIC -DSHARED -c -o stringrep.lo stringrep.c
> > >
> > > With that said, *i think its safe* to bump it back to '-D_FORTIFY_SOURCE=2'

I agree that 2 is the better value. I'll re-roll these to use 2. No
one seems to be complaining
on using the -D/-U options.

> > >
> > > >
> > > > >
> > > > >>
> > > > >> Signed-off-by: William Roberts <william.c.roberts@intel.com>
> > > > >> ---
> > > > >>   libselinux/src/Makefile   | 2 +-
> > > > >>   libselinux/utils/Makefile | 2 +-
> > > > >>   2 files changed, 2 insertions(+), 2 deletions(-)
> > > > >>
> > > > >> diff --git a/libselinux/src/Makefile b/libselinux/src/Makefile
> > > > >> index 977b5c8cfcca..ee55bd0dbff7 100644
> > > > >> --- a/libselinux/src/Makefile
> > > > >> +++ b/libselinux/src/Makefile
> > > > >> @@ -64,7 +64,7 @@ ifeq ($(COMPILER), gcc)
> > > > >>   EXTRA_CFLAGS = -fipa-pure-const -Wlogical-op
> > > > >> -Wpacked-bitfield-compat -Wsync-nand \
> > > > >>       -Wcoverage-mismatch -Wcpp -Wformat-contains-nul -Wnormalized=nfc
> > > > >> -Wsuggest-attribute=const \
> > > > >>       -Wsuggest-attribute=noreturn -Wsuggest-attribute=pure
> > > > >> -Wtrampolines -Wjump-misses-init \
> > > > >> -    -Wno-suggest-attribute=pure -Wno-suggest-attribute=const
> > > > >> -Wp,-D_FORTIFY_SOURCE
> > > > >> +    -Wno-suggest-attribute=pure -Wno-suggest-attribute=const
> > > > >> -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
> > > > >>   else
> > > > >>   EXTRA_CFLAGS = -Wunused-command-line-argument
> > > > >>   endif
> > > > >> diff --git a/libselinux/utils/Makefile b/libselinux/utils/Makefile
> > > > >> index d06ffd66893b..64ab877015c6 100644
> > > > >> --- a/libselinux/utils/Makefile
> > > > >> +++ b/libselinux/utils/Makefile
> > > > >> @@ -30,7 +30,7 @@ CFLAGS ?= -O -Wall -W -Wundef -Wformat-y2k
> > > > >> -Wformat-security -Winit-self -Wmissi
> > > > >>             -Wformat-extra-args -Wformat-zero-length -Wformat=2
> > > > >> -Wmultichar \
> > > > >>             -Woverflow -Wpointer-to-int-cast -Wpragmas \
> > > > >>             -Wno-missing-field-initializers -Wno-sign-compare \
> > > > >> -          -Wno-format-nonliteral
> > > > >> -Wframe-larger-than=$(MAX_STACK_SIZE) -Wp,-D_FORTIFY_SOURCE \
> > > > >> +          -Wno-format-nonliteral
> > > > >> -Wframe-larger-than=$(MAX_STACK_SIZE) -U_FORTIFY_SOURCE
> > > > >> -D_FORTIFY_SOURCE=1 \
> > > > >>             -fstack-protector-all --param=ssp-buffer-size=4
> > > > >> -fexceptions \
> > > > >>             -fasynchronous-unwind-tables -fdiagnostics-show-option
> > > > >> -funit-at-a-time \
> > > > >>             -Werror -Wno-aggregate-return -Wno-redundant-decls \