[PATCH 6.12.y 2/4] tracing: Use __free() for expr_str() buffer

[Sasha Levin <sashal@kernel.org>]

From: Pengpeng Hou <pengpeng@iscas.ac.cn>

[ Upstream commit 988995c0552b6213b6bf16cea57258d4842c1488 ]

expr_str() allocates a temporary expression buffer and manually frees it
on some error paths.

Convert the buffer to __free(kfree) and return it with return_ptr() on
success. This keeps ownership handling separate from the later ERR_PTR()
conversion and string-bound change.

Link: https://patch.msgid.link/20260611055945.22348-2-pengpeng@iscas.ac.cn
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Stable-dep-of: a0777b9e5315 ("tracing: Fix NULL dereference when copying keys for a field variable")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_events_hist.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 31563c47bb8d9..5e3232c405afc 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1751,7 +1751,7 @@ 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;
@@ -1762,7 +1762,7 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 	if (!field->operands[0]) {
 		expr_field_str(field, expr);
-		return expr;
+		return_ptr(expr);
 	}
 
 	if (field->operator == FIELD_OP_UNARY_MINUS) {
@@ -1770,16 +1770,15 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 		strcat(expr, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
-		if (!subexpr) {
-			kfree(expr);
+		if (!subexpr)
 			return NULL;
-		}
+
 		strcat(expr, subexpr);
 		strcat(expr, ")");
 
 		kfree(subexpr);
 
-		return expr;
+		return_ptr(expr);
 	}
 
 	expr_field_str(field->operands[0], expr);
@@ -1798,13 +1797,12 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 		strcat(expr, "*");
 		break;
 	default:
-		kfree(expr);
 		return NULL;
 	}
 
 	expr_field_str(field->operands[1], expr);
 
-	return expr;
+	return_ptr(expr);
 }
 
 /*
-- 
2.53.0