perf symbols: Fix return incorrect build_id size in elf_read_build_id()

In elf_read_build_id(), if gnu build_id is found, should return the size of
the actually copied data. If descsz is greater thanBuild_ID_SIZE,
write_buildid data access may occur.

Fixes: be96ea8 ("perf symbols: Fix issue with binaries using 16-bytes buildids (v2)")
Reported-by: Will Ochowicz <Will.Ochowicz@genusplc.com>
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Tested-by: Will Ochowicz <Will.Ochowicz@genusplc.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/lkml/CWLP265MB49702F7BA3D6D8F13E4B1A719C649@CWLP265MB4970.GBRP265.PROD.OUTLOOK.COM/T/
Link: https://lore.kernel.org/r/20230427012841.231729-1-yangjihong1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Yang Jihong

tools/perf/util/symbol-elf.c

@@ -886,7 +886,7 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
 				size_t sz = min(size, descsz);
 				memcpy(bf, ptr, sz);
 				memset(bf + sz, 0, size - sz);
-				err = descsz;
+				err = sz;
 				break;
 			}
 		}