[PATCH v4 1/2] tracing: Return ERR_PTR() from expr_str()

[Pengpeng Hou]

expr_str() already has failure cases for invalid recursion depth and
allocation failure, but it currently reports them as a bare NULL. Teach
it to return ERR_PTR()-encoded errors and update parse_unary() and
parse_expr() to propagate those errors.

This keeps the error conversion separate from the string-building change
so the follow-up seq_buf patch can stay focused on the overflow fix
itself.

Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
Changes since v3: https://lore.kernel.org/all/20260417223002.2-tracing-expr-v3-pengpeng@xxxxxxxxxxx/
- split the ERR_PTR() conversion into a separate patch as requested by
  Steven
- use __free(kfree) and return_ptr() in expr_str()
- propagate ERR_PTR() errors from parse_unary() and parse_expr()

 kernel/trace/trace_events_hist.c | 37 +++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 0dbbf6cca9bc..0b33bb8ef6f7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1769,18 +1769,18 @@ static void expr_field_str(struct hist_field *field, char *expr)
 
 static char *expr_str(struct hist_field *field, unsigned int level)
 {
-	char *expr;
+	char *expr __free(kfree) = NULL;
 
 	if (level > 1)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	expr = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
 	if (!expr)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	if (!field->operands[0]) {
 		expr_field_str(field, expr);
-		return expr;
+		return_ptr(expr);
 	}
 
 	if (field->operator == FIELD_OP_UNARY_MINUS) {
@@ -1788,16 +1788,15 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 		strcat(expr, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
-		if (!subexpr) {
-			kfree(expr);
-			return NULL;
-		}
+		if (IS_ERR(subexpr))
+			return subexpr;
+
 		strcat(expr, subexpr);
 		strcat(expr, ")");
 
 		kfree(subexpr);
 
-		return expr;
+		return_ptr(expr);
 	}
 
 	expr_field_str(field->operands[0], expr);
@@ -1816,13 +1815,12 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 		strcat(expr, "*");
 		break;
 	default:
-		kfree(expr);
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	expr_field_str(field->operands[1], expr);
 
-	return expr;
+	return_ptr(expr);
 }
 
 /*
@@ -2636,6 +2634,11 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 	expr->is_signed = operand1->is_signed;
 	expr->operator = FIELD_OP_UNARY_MINUS;
 	expr->name = expr_str(expr, 0);
+	if (IS_ERR(expr->name)) {
+		ret = PTR_ERR(expr->name);
+		expr->name = NULL;
+		goto free;
+	}
 	expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
 	if (!expr->type) {
 		ret = -ENOMEM;
@@ -2848,6 +2851,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		destroy_hist_field(operand1, 0);
 
 		expr->name = expr_str(expr, 0);
+		if (IS_ERR(expr->name)) {
+			ret = PTR_ERR(expr->name);
+			expr->name = NULL;
+			goto free_expr;
+		}
 	} else {
 		/* The operand sizes should be the same, so just pick one */
 		expr->size = operand1->size;
@@ -2861,6 +2869,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		}
 
 		expr->name = expr_str(expr, 0);
+		if (IS_ERR(expr->name)) {
+			ret = PTR_ERR(expr->name);
+			expr->name = NULL;
+			goto free_expr;
+		}
 	}
 
 	return expr;
-- 
2.50.1 (Apple Git-155)