[PATCH] tracing/histogram: Fix UAF in destroy_hist_field()

[Kalesh Singh <kaleshsingh@google.com>]

Calling destroy_hist_field() on an expression will recursively free
any operands associated with the expression. If during expression
parsing the operands of the expression are already set when an error
is encountered, there is no need to explicity free the operands. Doing
so will result in destroy_hist_field() being called twice for the
operands and lead to a use-after-free (UAF) error.

Fix this by only calling destroy_hist_field() for the expression if the
operands are already set.

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Fixes: 8b5d46fd7a38 ("tracing/histogram: Optimize division by constants")
Reported-by: kernel test robot <oliver.sang@intel.com>
---
 kernel/trace/trace_events_hist.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 5ea2c9ec54a6..e3856eaf2ac3 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2669,7 +2669,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		if (!divisor) {
 			hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
 			ret = -EDOM;
-			goto free;
+			goto free_expr;
 		}
 
 		/*
@@ -2709,7 +2709,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
 		if (!expr->type) {
 			ret = -ENOMEM;
-			goto free;
+			goto free_expr;
 		}
 
 		expr->name = expr_str(expr, 0);
@@ -2719,6 +2719,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 free:
 	destroy_hist_field(operand1, 0);
 	destroy_hist_field(operand2, 0);
+free_expr:
 	destroy_hist_field(expr, 0);
 
 	return ERR_PTR(ret);

base-commit: 8ab774587903771821b59471cc723bba6d893942
-- 
2.34.0.rc1.387.gb447b232ab-goog