[PATCH bpf v2 1/3] bpf, tcx: reject offloaded programs on attach

[Jiayuan Chen <jiayuan.chen@linux.dev>]

An offloaded prog's bpf_func is replaced by bpf_prog_warn_on_exec(),
since it's supposed to run on the NIC, not the host. But tcx doesn't
check this and happily attaches it to the software path, so the first
packet hits the WARN.

XDP already guards this in dev_xdp_attach(); tcx just never got the
same check. Add it to tcx_prog_attach(), tcx_link_attach() and also
tcx_link_update() so the fix cannot be bypassed by loading a normal
program and then swapping it out via BPF_LINK_UPDATE.

Use bpf_prog_is_offloaded() rather than bpf_prog_is_dev_bound() +
bpf_offload_dev_match() (as XDP does): bpf_prog_dev_bound_init()
already rejects BPF_F_XDP_DEV_BOUND_ONLY for BPF_PROG_TYPE_SCHED_CLS,
so a dev-bound SCHED_CLS program is always offloaded. The simpler
check is sufficient and also rejects attaching a program offloaded to
device A onto device B.

Fixes: e420bed025071 ("bpf: Add fd-based tcx multi-prog infra with link support")
Reported-by: Yinhao Hu <dddddd@hust.edu.cn>
Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
Reported-by: Dongliang Mu <dzm91@hust.edu.cn>
Closes: https://lore.kernel.org/bpf/64d8e2b5-a214-4f3c-b9e8-bcedbcb2c602@hust.edu.cn/
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 kernel/bpf/tcx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/bpf/tcx.c b/kernel/bpf/tcx.c
index 02db0113b8e7c..1144627483d53 100644
--- a/kernel/bpf/tcx.c
+++ b/kernel/bpf/tcx.c
@@ -16,6 +16,9 @@ int tcx_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct net_device *dev;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = __dev_get_by_index(net, attr->target_ifindex);
 	if (!dev) {
@@ -209,6 +212,9 @@ static int tcx_link_update(struct bpf_link *link, struct bpf_prog *nprog,
 	struct net_device *dev;
 	int ret = 0;
 
+	if (bpf_prog_is_offloaded(nprog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = tcx->dev;
 	if (!dev) {
@@ -315,6 +321,9 @@ int tcx_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	struct tcx_link *tcx;
 	int ret;
 
+	if (bpf_prog_is_offloaded(prog->aux))
+		return -EINVAL;
+
 	rtnl_lock();
 	dev = __dev_get_by_index(net, attr->link_create.target_ifindex);
 	if (!dev) {
-- 
2.43.0