[PATCH v5 2/3] tracing: Return ERR_PTR() from expr_str()

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

expr_str() currently reports all failure cases as NULL, so callers cannot
distinguish invalid recursion depth from allocation failure or later
string construction errors.

Return ERR_PTR()-encoded errors from expr_str() and make parse_unary()
and parse_expr() propagate them. Clear expr->name before destroying the
hist field so the error pointer is not freed as a string.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 kernel/trace/trace_events_hist.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f778f060e922..082842e64ccd 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1762,11 +1762,11 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 	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);
@@ -1778,8 +1778,8 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 		strcat(expr, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
-		if (!subexpr)
-			return NULL;
+		if (IS_ERR(subexpr))
+			return subexpr;
 
 		strcat(expr, subexpr);
 		strcat(expr, ")");
@@ -1805,7 +1805,7 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 		strcat(expr, "*");
 		break;
 	default:
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	expr_field_str(field->operands[1], expr);
@@ -2624,6 +2624,11 @@ 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;
@@ -2836,6 +2841,11 @@ 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;
@@ -2849,6 +2859,11 @@ 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)