[PATCH v2 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[Ian Rogers <irogers@google.com>]

Fix potential buffer overruns in perf_event__synthesize_modules_maps_cb()
by safely clamping long DSO names to the mmap/mmap2 filename boundaries.
Explicitly assign and clear the misc flags and union padding across all
iterations to prevent stale Build-ID state from leaking between module
synthesis events.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 70 +++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 9a2b4d561e9e..068323b9510d 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -754,6 +754,7 @@ struct perf_event__synthesize_modules_maps_cb_args {
 	perf_event__handler_t process;
 	struct machine *machine;
 	union perf_event *event;
+	u16 misc;
 };
 
 static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
@@ -761,49 +762,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 	struct perf_event__synthesize_modules_maps_cb_args *args = data;
 	union perf_event *event = args->event;
 	struct dso *dso;
-	size_t size;
+	size_t size, aligned_size;
+	int rc = 0;
 
 	if (!__map__is_kmodule(map))
 		return 0;
 
 	dso = map__dso(map);
 	if (!symbol_conf.no_buildid_mmap2) {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap2.filename))
+			size = sizeof(event->mmap2.filename) - 1;
+
+		strlcpy(event->mmap2.filename, long_name,
+			sizeof(event->mmap2.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap2.header.type = PERF_RECORD_MMAP2;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - size));
-		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap2.header.misc = args->misc;
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap2.header.size += args->machine->id_hdr_size;
 		event->mmap2.start = map__start(map);
 		event->mmap2.len   = map__size(map);
 		event->mmap2.pid   = args->machine->pid;
 
-		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
-
-		/* Clear stale build ID from previous module iteration */
+		/* Clear stale build ID and entire union from previous module iteration */
 		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
 		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
 		event->mmap2.build_id_size = 0;
+		event->mmap2.__reserved_1 = 0;
+		event->mmap2.__reserved_2 = 0;
 
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap.filename))
+			size = sizeof(event->mmap.filename) - 1;
+
+		strlcpy(event->mmap.filename, long_name,
+			sizeof(event->mmap.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap.header.type = PERF_RECORD_MMAP;
-		event->mmap.header.size = (sizeof(event->mmap) -
-					(sizeof(event->mmap.filename) - size));
-		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap.header.misc = args->misc;
+		event->mmap.header.size =
+			offsetof(struct perf_record_mmap, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap.header.size += args->machine->id_hdr_size;
 		event->mmap.start = map__start(map);
 		event->mmap.len   = map__size(map);
 		event->mmap.pid   = args->machine->pid;
-
-		memcpy(event->mmap.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 	}
 
 	if (perf_tool__process_synth_event(args->tool, event, args->machine, args->process) != 0)
-		return -1;
+		rc = -1;
 
-	return 0;
+	return rc;
 }
 
 int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process,
@@ -828,13 +858,13 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
 	}
 
 	/*
-	 * kernel uses 0 for user space maps, see kernel/perf_event.c
-	 * __perf_event_mmap
+	 * Just like the kernel, see perf_misc_flags() in
+	 * kernel/events/core.c
 	 */
 	if (machine__is_host(machine))
-		args.event->header.misc = PERF_RECORD_MISC_KERNEL;
+		args.misc = PERF_RECORD_MISC_KERNEL;
 	else
-		args.event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
+		args.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
 	rc = maps__for_each_map(maps, perf_event__synthesize_modules_maps_cb, &args);
 
-- 
2.55.0.229.g6434b31f56-goog