tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields

[ Upstream commit a244c241593b5b38a08f0df2cb43c26574efbdcb ]

In check_synth_field(), when a synthetic event field is a stacktrace (field->is_stack) and the histogram field is not a "long[" stacktrace array, validation falls through to the generic size and signedness comparison.

Because parse_synth_field() sets a stacktrace field's type to "__data_loc unsigned long[]", its size is sizeof(u64) and synth_field_signed() marks it as signed. Consequently, any 8-byte signed scalar histogram field passes the fallback check, and its scalar value is subsequently dereferenced as a kernel stacktrace pointer in get_field_size() and trace_stack().

Furthermore, checking strstr(hist_field->type, "long[") is insufficient because tracepoint fields defined with __bitmask() or __rel_bitmask() also have type "__data_loc unsigned long[]" or "__rel_loc unsigned long[]", whilst create_hist_field() treats them as 4-byte scalar values without HIST_FIELD_FL_STACKTRACE.

Propagate HIST_FIELD_FL_STACKTRACE to variable references and field variables (whilst excluding variable aliases from per-element stacktrace capture), and reject any mismatch between HIST_FIELD_FL_STACKTRACE and field->is_stack in check_synth_field().

[Lee: Omit create_var_field() and hist_trigger_elt_update() hunks as
288709c9f3b0 ("tracing: Allow stacktraces to be saved as histogram variables") is not present]

---
 kernel/trace/trace_events_hist.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

index 8e5efdfa0fc7..b8fb45fa3cfc 100644
@@ -2066,7 +2066,8 @@ static int init_var_ref(struct hist_field *ref_field,
 	ref_field->size = var_field->size;
 	ref_field->is_signed = var_field->is_signed;
 	ref_field->flags |= var_field->flags &
-		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
+		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS |
+		 HIST_FIELD_FL_STACKTRACE);
 
 	if (system) {
 		ref_field->system = kstrdup(system, GFP_KERNEL);

@@ -3203,6 +3204,7 @@ static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
 		ret =  -ENOMEM;
 		goto err;
 	}
+	var->flags |= val->flags & HIST_FIELD_FL_STACKTRACE;
 
 	field_var->var = var;
 	field_var->val = val;

@@ -3820,7 +3822,10 @@ static int check_synth_field(struct synth_event *event,
 	    && field->is_dynamic)
 		return 0;
 
-	if (strstr(hist_field->type, "long[") && field->is_stack)
+	if (!!(hist_field->flags & HIST_FIELD_FL_STACKTRACE) != field->is_stack)
+		return -EINVAL;
+
+	if (field->is_stack)
 		return 0;
 
 	if (strcmp(field->type, hist_field->type) != 0) {

2.56.0.257.gf7497c7d27-goog