Re: [Qemu-devel] [PATCH] tests/Makefile: Suppress format-security warnings on JSON tests

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/02/2014 23:47, Peter Maydell ha scritto:
> Some of our test binaries programmatically generate JSON format
> strings to feed to qobject_from_json(). Since that function is
> marked with GCC_FMT_ATTR(), clang complains about this:
>  tests/test-qmp-input-visitor.c:76:35: warning: format string is not a
>  string literal (potentially insecure) [-Wformat-security]
>     data->obj = qobject_from_json(json_string);
>                                   ^~~~~~~~~~~

qobject_from_json shouldn't have a GCC_FMT_ATTR marker, only 
qobject_from_jsonf and qobject_from_jsonv.

qobject_from_json passes a NULL va_list*, and then parse_escape in 
qobject/json-parser.c returns NULL before calling va_arg.  Ultimately 
this produces a parse error.

Paolo

> Since these are only test cases and not potential attack vectors,
> the simplest approach is simply to suppress this particular
> compiler warning when compiling the relevant test cases.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I couldn't think of a better way to do this...
>
>  tests/Makefile | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/tests/Makefile b/tests/Makefile
> index b17d41e..496c02f 100644
> --- a/tests/Makefile
> +++ b/tests/Makefile
> @@ -146,6 +146,17 @@ check-qapi-schema-y := $(addprefix tests/qapi-schema/, \
>
>  GENERATED_HEADERS += tests/test-qapi-types.h tests/test-qapi-visit.h tests/test-qmp-commands.h
>
> +# These tests use the qobject_from_json() function with programmatically
> +# generated format strings; since this would otherwise trip clang's
> +# format-security warnings and these are only test binaries, disable
> +# the warnings when building them.
> +JSON_USERS=check-qjson \
> +           check-input-visitor \
> +           test-qmp-input-visitor \
> +           test-visitor-serialization
> +
> +$(JSON_USERS:%=tests/%.o): CFLAGS += -Wno-format-security
> +
>  test-obj-y = tests/check-qint.o tests/check-qstring.o tests/check-qdict.o \
>  	tests/check-qlist.o tests/check-qfloat.o tests/check-qjson.o \
>  	tests/test-coroutine.o tests/test-string-output-visitor.o \
>