From: Jesper Dangaard Brouer <brouer@redhat.com>
To: bpf@vger.kernel.org
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
netdev@vger.kernel.org, Daniel Borkmann <borkmann@iogearbox.net>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: [PATCH bpf V3 1/2] bpf: BPF-helper for MTU checking add length input
Date: Mon, 08 Mar 2021 15:59:18 +0100 [thread overview]
Message-ID: <161521555850.3515614.6533850861569774444.stgit@firesoul> (raw)
In-Reply-To: <161521552920.3515614.3831682841593366034.stgit@firesoul>
The FIB lookup example[1] show how the IP-header field tot_len
(iph->tot_len) is used as input to perform the MTU check.
This patch extend the BPF-helper bpf_check_mtu() with the same ability
to provide the length as user parameter input, via mtu_len parameter.
[1] samples/bpf/xdp_fwd_kern.c
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
---
include/uapi/linux/bpf.h | 16 +++++++++++-----
net/core/filter.c | 12 ++++++++++--
2 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 79c893310492..4ba4ef0ff63a 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 adfdad234674..9323d34d34cc 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;
next prev parent reply other threads:[~2021-03-08 15:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 14:59 [PATCH bpf V3 0/2] bpf: Updates for BPF-helper bpf_check_mtu Jesper Dangaard Brouer
2021-03-08 14:59 ` Jesper Dangaard Brouer [this message]
2021-03-08 14:59 ` [PATCH bpf V3 2/2] selftests/bpf: Tests using bpf_check_mtu BPF-helper input mtu_len param Jesper Dangaard Brouer
2021-03-08 21:50 ` [PATCH bpf V3 0/2] bpf: Updates for BPF-helper bpf_check_mtu patchwork-bot+netdevbpf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=161521555850.3515614.6533850861569774444.stgit@firesoul \
--to=brouer@redhat.com \
--cc=alexei.starovoitov@gmail.com \
--cc=borkmann@iogearbox.net \
--cc=bpf@vger.kernel.org \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).