diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 79c893310492b33689352b9dff5f53a42dd9d72b..4ba4ef0ff63a4084a065a9228be99a641594c6ce 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3850,7 +3850,7 @@ union bpf_attr { * * long bpf_check_mtu(void *ctx, u32 ifindex, u32 *mtu_len, s32 len_diff, u64 flags) * Description - * Check ctx packet size against exceeding MTU of net device (based + * Check packet size against exceeding MTU of net device (based * on *ifindex*). This helper will likely be used in combination * with helpers that adjust/change the packet size. * @@ -3867,6 +3867,14 @@ union bpf_attr { * against the current net device. This is practical if this isn't * used prior to redirect. * + * On input *mtu_len* must be a valid pointer, else verifier will + * reject BPF program. If the value *mtu_len* is initialized to + * zero then the ctx packet size is use. When value *mtu_len* is + * provided as input this specify the L3 length that the MTU check + * is done against. Remember XDP and TC length operate at L2, but + * this value is L3 as this correlate to MTU and IP-header tot_len + * values which are L3 (similar behavior as bpf_fib_lookup). + * * The Linux kernel route table can configure MTUs on a more * specific per route level, which is not provided by this helper. * For route level MTU checks use the **bpf_fib_lookup**\ () @@ -3891,11 +3899,9 @@ union bpf_attr { * * On return *mtu_len* pointer contains the MTU value of the net * device. Remember the net device configured MTU is the L3 size, - * which is returned here and XDP and TX length operate at L2. + * which is returned here and XDP and TC length operate at L2. * Helper take this into account for you, but remember when using - * MTU value in your BPF-code. On input *mtu_len* must be a valid - * pointer and be initialized (to zero), else verifier will reject - * BPF program. + * MTU value in your BPF-code. * * Return * * 0 on success, and populate MTU value in *mtu_len* pointer. diff --git a/net/core/filter.c b/net/core/filter.c index adfdad234674dc1031d24b8ae635174fcfbd0dce..9323d34d34cccbf8724bc7b2c937387a2cbcc0a6 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5658,7 +5658,7 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb, if (unlikely(flags & ~(BPF_MTU_CHK_SEGS))) return -EINVAL; - if (unlikely(flags & BPF_MTU_CHK_SEGS && len_diff)) + if (unlikely(flags & BPF_MTU_CHK_SEGS && (len_diff || *mtu_len))) return -EINVAL; dev = __dev_via_ifindex(dev, ifindex); @@ -5668,7 +5668,11 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb, mtu = READ_ONCE(dev->mtu); dev_len = mtu + dev->hard_header_len; - skb_len = skb->len + len_diff; /* minus result pass check */ + + /* If set use *mtu_len as input, L3 as iph->tot_len (like fib_lookup) */ + skb_len = *mtu_len ? *mtu_len + dev->hard_header_len : skb->len; + + skb_len += len_diff; /* minus result pass check */ if (skb_len <= dev_len) { ret = BPF_MTU_CHK_RET_SUCCESS; goto out; @@ -5713,6 +5717,10 @@ BPF_CALL_5(bpf_xdp_check_mtu, struct xdp_buff *, xdp, /* Add L2-header as dev MTU is L3 size */ dev_len = mtu + dev->hard_header_len; + /* Use *mtu_len as input, L3 as iph->tot_len (like fib_lookup) */ + if (*mtu_len) + xdp_len = *mtu_len + dev->hard_header_len; + xdp_len += len_diff; /* minus result pass check */ if (xdp_len > dev_len) ret = BPF_MTU_CHK_RET_FRAG_NEEDED;