[PATCH 07/29] perf session: Fix swap_sample_id_all() crash on crafted events

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

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

swap_sample_id_all() calls BUG_ON(size % sizeof(u64)) which kills
perf on any event where the sample_id_all tail is not 8-byte aligned.
A crafted perf.data can trigger this trivially.

Replace BUG_ON with a bounds check: skip the swap if the data pointer
is past the end of the event, and only swap when there are bytes
remaining.

Note: the strlen calls in string-field swap handlers (comm,
mmap, mmap2, cgroup) are replaced with bounded strnlen by the
next patch in this series ("perf session: Add validated swap
infrastructure with null-termination checks").

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 | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 24f2ba599b8079bd..37544a3574185bac 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -276,10 +276,18 @@ void perf_session__delete(struct perf_session *session)
 static void swap_sample_id_all(union perf_event *event, void *data)
 {
 	void *end = (void *) event + event->header.size;
-	int size = end - data;
+	int size;
 
-	BUG_ON(size % sizeof(u64));
-	mem_bswap_64(data, size);
+	if (data >= end)
+		return;
+
+	size = end - data;
+	if (size % sizeof(u64)) {
+		pr_warning("swap_sample_id_all: unaligned sample_id_all remainder (%d), skipping swap\n", size);
+		return;
+	}
+	if (size > 0)
+		mem_bswap_64(data, size);
 }
 
 static void perf_event__all64_swap(union perf_event *event,
-- 
2.54.0