[PATCH 08/28] perf session: Use bounded copy for PERF_RECORD_TIME_CONV

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

session->time_conv = event->time_conv copies sizeof(struct
perf_record_time_conv) bytes unconditionally, but older kernels
emit shorter TIME_CONV events without the time_cycles, time_mask,
cap_user_time_zero, and cap_user_time_short fields.

For a 32-byte event (the original format), this reads 24 bytes
past the event boundary into adjacent mmap'd data.  The garbage
values end up in session->time_conv and can cause incorrect TSC
conversion if cap_user_time_zero happens to be non-zero.

Replace the struct assignment with a bounded memcpy capped at
event->header.size, zeroing the remainder so extended fields
default to off when absent.

Reported-by: sashiko-bot@kernel.org # Running on a local machine
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/session.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 18e60ccf6829f05a..776061afd568858a 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1894,7 +1894,14 @@ static s64 perf_session__process_user_event(struct perf_session *session,
 		err = tool->stat_round(tool, session, event);
 		break;
 	case PERF_RECORD_TIME_CONV:
-		session->time_conv = event->time_conv;
+		/*
+		 * Bounded copy: older kernels emit a shorter struct
+		 * without time_cycles/time_mask/cap_user_time_*.
+		 * Zero the rest so extended fields default to off.
+		 */
+		memset(&session->time_conv, 0, sizeof(session->time_conv));
+		memcpy(&session->time_conv, &event->time_conv,
+		       min((size_t)event->header.size, sizeof(session->time_conv)));
 		err = tool->time_conv(tool, session, event);
 		break;
 	case PERF_RECORD_HEADER_FEATURE:
-- 
2.54.0