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>,
maze@google.com, lmb@cloudflare.com, shaun@tigera.io,
Lorenzo Bianconi <lorenzo@kernel.org>,
marek@cloudflare.com, John Fastabend <john.fastabend@gmail.com>,
Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH bpf-next V1 1/6] bpf: Remove MTU check in __bpf_skb_max_len
Date: Tue, 06 Oct 2020 18:02:51 +0200 [thread overview]
Message-ID: <160200017146.719143.8604341963140667595.stgit@firesoul> (raw)
In-Reply-To: <160200013701.719143.12665708317930272219.stgit@firesoul>
Multiple BPF-helpers that can manipulate/increase the size of the SKB uses
__bpf_skb_max_len() as the max-length. This function limit size against
the current net_device MTU (skb->dev->mtu).
When a BPF-prog grow the packet size, then it should not be limited to the
MTU. The MTU is a transmit limitation, and software receiving this packet
should be allowed to increase the size. Further more, current MTU check in
__bpf_skb_max_len uses the MTU from ingress/current net_device, which in
case of redirects uses the wrong net_device.
Keep a sanity max limit of IP_MAX_MTU which is 64KiB.
In later patches we will enforce the MTU limitation when transmitting
packets.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
(imported from commit 37f8552786cf46588af52b77829b730dd14524d3)
---
net/core/filter.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 05df73780dd3..fed239e77bdc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3476,8 +3476,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
static u32 __bpf_skb_max_len(const struct sk_buff *skb)
{
- return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
- SKB_MAX_ALLOC;
+ return IP_MAX_MTU;
}
BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
next prev parent reply other threads:[~2020-10-06 16:03 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-06 16:02 [PATCH bpf-next V1 0/6] bpf: New approach for BPF MTU handling and enforcement Jesper Dangaard Brouer
2020-10-06 16:02 ` Jesper Dangaard Brouer [this message]
2020-10-06 16:02 ` [PATCH bpf-next V1 2/6] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2020-10-07 1:34 ` Maciej Żenczykowski
2020-10-07 7:42 ` Jesper Dangaard Brouer
2020-10-07 16:38 ` David Ahern
2020-10-07 7:28 ` kernel test robot
2020-10-06 16:03 ` [PATCH bpf-next V1 3/6] bpf: add BPF-helper for reading MTU from net_device via ifindex Jesper Dangaard Brouer
2020-10-06 16:33 ` Jesper Dangaard Brouer
2020-10-07 1:18 ` Jakub Kicinski
2020-10-07 1:24 ` Maciej Żenczykowski
2020-10-07 7:53 ` Jesper Dangaard Brouer
2020-10-07 16:35 ` David Ahern
2020-10-07 17:44 ` Maciej Żenczykowski
2020-10-06 16:03 ` [PATCH bpf-next V1 4/6] bpf: make it possible to identify BPF redirected SKBs Jesper Dangaard Brouer
2020-10-06 16:03 ` [PATCH bpf-next V1 5/6] bpf: Add MTU check for TC-BPF packets after egress hook Jesper Dangaard Brouer
2020-10-06 20:09 ` kernel test robot
2020-10-07 0:26 ` kernel test robot
2020-10-06 16:03 ` [PATCH bpf-next V1 6/6] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
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