Re: [PATCH v10 bpf-next 1/2] bpf: test_run: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap

[Martin KaFai Lau]

On 3/4/26 2:33 AM, Leon Hwang wrote:

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 178c4738e63b..565fe8cbcdc9 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1156,6 +1156,20 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const 
union bpf_attr *kattr,
                skb->ip_summed = CHECKSUM_COMPLETE;
        }

+ if (prog->type == BPF_PROG_TYPE_LWT_XMIT) {

+               if (ipv6_bpf_stub) {
+#if IS_ENABLED(CONFIG_IPV6)
+                       dst_hold(&net->ipv6.ip6_null_entry->dst);
+                       skb_dst_set(skb, &net->ipv6.ip6_null_entry->dst);
+#endif
+               } else {
+                       /* For CONFIG_IPV6=n, ipv6_bpf_stub is NULL */
+                       pr_warn_once("Please test this program with the IPv6 module 
enabled\n");
+                       ret = -EOPNOTSUPP;
+                       goto out;
+               }
+       }
+

NIT: it would be more readable to handle the error path first.

if (prog->type == BPF_PROG_TYPE_LWT_XMIT) {
        if (!ipv6_bpf_stub) {
                pr_warn_once("...");
                ret = -EOPNOTSUPP;
                goto out;
        }
#if IS_ENABLED(CONFIG_IPV6)
        dst_hold();
        skb_dst_set();
#endif

I have adapted this change and applied. Thanks.