[PATCH v2] perf buildid: Avoid copy of uninitialized memory

[Ian Rogers <irogers@google.com>]

build_id__init only copies the buildid data up to size leaving the
rest of the data array uninitialized. Copying the full array during
synthesis means the written event contains uninitialized
memory. Ensure the size is less that the buffer size and only copy the
bytes that were initialized. This was detected by the Clang/LLVM
memory sanitizer.

Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ian Rogers <irogers@google.com>

v2. Avoids the potential for copying too much as suggested by Arnaldo.
---
 tools/perf/util/synthetic-events.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 3ab6a92b1a6d..9ab9308ee80c 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -2219,8 +2219,8 @@ int perf_event__synthesize_build_id(struct perf_tool *tool, struct dso *pos, u16
 
 	len = pos->long_name_len + 1;
 	len = PERF_ALIGN(len, NAME_ALIGN);
-	memcpy(&ev.build_id.build_id, pos->bid.data, sizeof(pos->bid.data));
-	ev.build_id.size = pos->bid.size;
+	ev.build_id.size = min(pos->bid.size, sizeof(pos->bid.data));
+	memcpy(&ev.build_id.build_id, pos->bid.data, ev.build_id.size);
 	ev.build_id.header.type = PERF_RECORD_HEADER_BUILD_ID;
 	ev.build_id.header.misc = misc | PERF_RECORD_MISC_BUILD_ID_SIZE;
 	ev.build_id.pid = machine->pid;
-- 
2.39.0.246.g2a6d74b583-goog