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bpf: Introduce SK_LOOKUP program type with a dedicated attach point

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Add a new program type BPF_PROG_TYPE_SK_LOOKUP with a dedicated attach type
BPF_SK_LOOKUP. The new program kind is to be invoked by the transport layer
when looking up a listening socket for a new connection request for
connection oriented protocols, or when looking up an unconnected socket for
a packet for connection-less protocols.

When called, SK_LOOKUP BPF program can select a socket that will receive
the packet. This serves as a mechanism to overcome the limits of what
bind() API allows to express. Two use-cases driving this work are:

 (1) steer packets destined to an IP range, on fixed port to a socket

     192.0.2.0/24, port 80 -> NGINX socket

 (2) steer packets destined to an IP address, on any port to a socket

     198.51.100.1, any port -> L7 proxy socket

In its run-time context program receives information about the packet that
triggered the socket lookup. Namely IP version, L4 protocol identifier, and
address 4-tuple. Context can be further extended to include ingress
interface identifier.

To select a socket BPF program fetches it from a map holding socket
references, like SOCKMAP or SOCKHASH, and calls bpf_sk_assign(ctx, sk, ...)
helper to record the selection. Transport layer then uses the selected
socket as a result of socket lookup.

In its basic form, SK_LOOKUP acts as a filter and hence must return either
SK_PASS or SK_DROP. If the program returns with SK_PASS, transport should
look for a socket to receive the packet, or use the one selected by the
program if available, while SK_DROP informs the transport layer that the
lookup should fail.

This patch only enables the user to attach an SK_LOOKUP program to a
network namespace. Subsequent patches hook it up to run on local delivery
path in ipv4 and ipv6 stacks.

Suggested-by: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200717103536.397595-3-jakub@cloudflare.com
This commit is contained in:
Jakub Sitnicki 2020-07-17 12:35:23 +02:00 • committed by Alexei Starovoitov
parent ce3aa9cc51
commit e9ddbb7707
10 changed files with 312 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

9
scripts/bpf_helpers_doc.py
View file

@ -404,6 +404,7 @@ class PrinterHelpers(Printer):
type_fwds = [
'struct bpf_fib_lookup',
'struct bpf_sk_lookup',
'struct bpf_perf_event_data',
'struct bpf_perf_event_value',
'struct bpf_pidns_info',
@ -450,6 +451,7 @@ class PrinterHelpers(Printer):
'struct bpf_perf_event_data',
'struct bpf_perf_event_value',
'struct bpf_pidns_info',
'struct bpf_sk_lookup',
'struct bpf_sock',
'struct bpf_sock_addr',
'struct bpf_sock_ops',
@ -487,6 +489,11 @@ class PrinterHelpers(Printer):
'struct sk_msg_buff': 'struct sk_msg_md',
'struct xdp_buff': 'struct xdp_md',
}
# Helpers overloaded for different context types.
overloaded_helpers = [
'bpf_get_socket_cookie',
'bpf_sk_assign',
]
def print_header(self):
header = '''\
@ -543,7 +550,7 @@ class PrinterHelpers(Printer):
for i, a in enumerate(proto['args']):
t = a['type']
n = a['name']
if proto['name'] == 'bpf_get_socket_cookie' and i == 0:
if proto['name'] in self.overloaded_helpers and i == 0:
t = 'void'
n = 'ctx'
one_arg = '{}{}'.format(comma, self.map_type(t))