perf header: Sanity check HEADER_GROUP_DESC

Add upper bound check on nr_groups in process_group_desc() to harden
against malformed perf.data files (max 32768), and move the env
assignment after validation.

Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Assisted-by: Claude Code:claude-opus-4-6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: acmel

tools/perf/util/header.c

@@ -63,6 +63,7 @@
 #include <event-parse.h>
 #endif
 
+#define MAX_GROUP_DESC		32768
 #define MAX_NUMA_NODES		4096
 #define MAX_PMU_MAPPINGS	4096
 #define MAX_SCHED_DOMAINS	64
@@ -3132,12 +3133,25 @@ static int process_group_desc(struct feat_fd *ff, void *data __maybe_unused)
 	if (do_read_u32(ff, &nr_groups))
 		return -1;
 
-	env->nr_groups = nr_groups;
 	if (!nr_groups) {
 		pr_debug("group desc not available\n");
 		return 0;
 	}
 
+	if (nr_groups > MAX_GROUP_DESC) {
+		pr_err("Invalid HEADER_GROUP_DESC: nr_groups (%u) > %u\n",
+		       nr_groups, MAX_GROUP_DESC);
+		return -1;
+	}
+
+	if (ff->size < sizeof(u32) + nr_groups * 3 * sizeof(u32)) {
+		pr_err("Invalid HEADER_GROUP_DESC: section too small (%zu) for %u groups\n",
+		       ff->size, nr_groups);
+		return -1;
+	}
+
+	env->nr_groups = nr_groups;
+
 	desc = calloc(nr_groups, sizeof(*desc));
 	if (!desc)
 		return -1;