[PATCH nft,v2] netlink_delinearize: fix use-after-free

[PATCH nft,v2] netlink_delinearize: fix use-after-free

[Pablo Neira Ayuso]

We have to clone the payload expression before attaching it to the lhs
of the relational expression, this payload expression is located at the
lhs of the binary operation that is released thereafter.

Fixes: 39f15c2 ("nft: support listing expressions that use non-byte header fields")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
v2: use expr_get() instead to avoid the extra cost of cloning.

 src/netlink_delinearize.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/netlink_delinearize.c b/src/netlink_delinearize.c
index b119027..6ae7267 100644
--- a/src/netlink_delinearize.c
+++ b/src/netlink_delinearize.c
@@ -1217,8 +1217,8 @@ static void relational_binop_postprocess(struct rule_pp_ctx *ctx, struct expr *e
 	} else if (binop->op == OP_AND &&
 		   binop->left->ops->type == EXPR_PAYLOAD &&
 		   binop->right->ops->type == EXPR_VALUE) {
-		struct expr *payload = expr->left->left;
-		struct expr *mask = expr->left->right;
+		struct expr *payload = binop->left;
+		struct expr *mask = binop->right;
 
 		/*
 		 * This *might* be a payload match testing header fields that
@@ -1266,7 +1266,7 @@ static void relational_binop_postprocess(struct rule_pp_ctx *ctx, struct expr *e
 			assert(expr->left->ops->type == EXPR_BINOP);
 
 			assert(binop->left == payload);
-			expr->left = payload;
+			expr->left = expr_get(payload);
 			expr_free(binop);
 		}
 	}
-- 
2.1.4