[PATCH v3 5/5] telemetry: remove VLA in json string format function

[David Marchand]

On Wed, Apr 5, 2023 at 6:05 PM Bruce Richardson
<bruce.richardson at intel.com> wrote:
>
> Since variable length arrays (VLAs) are potentially insecure and
> unsupported by some compilers, rework the code to remove their use. As
> with previous changes to remove VLAs in the telemetry code, this
> function uses two methods to avoid modifying the buffer when adding to
> it fails:
> * if there are only a few characters in the buffer, save them off to
>   restore on failure, then use the buffer as-is,
> * otherwise use malloc rather than a VLA to allocate a temporary buffer
>   and copy from that on success only.
>
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> ---
>  app/test/test_telemetry_json.c |  2 +-
>  lib/telemetry/telemetry_json.h | 19 +++++++++++++++++--
>  2 files changed, 18 insertions(+), 3 deletions(-)

This change triggers a unit test failure ("interestingly" only with
gcc, I can't reproduce with clang).

$ ninja -C build-gcc && ./build-gcc/app/test/dpdk-test --no-huge -m
2048 --iova=va -- telemetry_json_autotest
ninja: Entering directory `build-gcc'
ninja: no work to do.
EAL: Detected CPU lcores: 16
EAL: Detected NUMA nodes: 1
EAL: Detected shared linkage of DPDK
EAL: Multi-process socket /run/user/114840/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'VA'
APP: HPET is not enabled, using TSC as default timer
RTE>>telemetry_json_autotest
test_basic_array: buf = '["meaning of life",42]', expected =
'["meaning of life",42]'
OK
test_basic_obj: buf = '{"weddings":4,"funerals":1}', expected =
'{"weddings":4,"funerals":1}'
OK
test_overflow_array: buf = '', expected = '["Arsenal","Chelsea"]'
ERROR
Test Failed


I guess we need:

diff --git a/lib/telemetry/telemetry_json.h b/lib/telemetry/telemetry_json.h
index 7999535848..7a246deacb 100644
--- a/lib/telemetry/telemetry_json.h
+++ b/lib/telemetry/telemetry_json.h
@@ -153,7 +153,7 @@ __json_format_str(char *buf, const int len, const
char *prefix, const char *str,

        ret = __json_format_str_to_buf(tmp, len, prefix, str, suffix);
        if (ret > 0)
-               strcpy(buf, saved);
+               strcpy(buf, tmp);

        free(tmp);
        return ret;


-- 
David Marchand