[RFC,v3,net-next,0/5] eBPF and struct scatterlist

This is v3 of the RFC sent earlier,
(https://patchwork.ozlabs.org/cover/931785/).

v2->v3:
- As per the review feedback received, this patchset reuses as much code
as possible from sockmap/sk_msg. e.g. it uses existing struct
sk_msg_buff, struct sk_msg_md, sk_msg_convert_ctx_access and part of
code from sk_msg_convert_ctx_access.

- bpf helper bpf_msg_pull_data() is used to access packet data. Some
issues found with bpf_msg_pull_data() are therefore fixed in patch 3.

- A feedback was given that unprivileged user can attach a new
BPF_PROG_TYPE_SOCKET_SG_FILTER to a non-rds socket e.g. normal tcp/udp
through the SO_ATTACH_BPF sockopt, where input context is skb instead of
sg list and can cause issues. However, I found that as an unprivileged,
user can attach any kind of eBPF program to socket using SO_ATTACH_BPF,
not only socksg. But if eBPF program is faulty, kernel BPF verifier take
care of it and invalidate any access to kernel data, doesn't let eBPF
program to run.

- socksg programs now returns action code (e.g. SOCKSG_PASS etc,.).


Background:
The motivation for this work is to allow eBPF based firewalling for
kernel modules that do not always get their packet as an sk_buff from
their downlink drivers. One such instance of this use-case is RDS, which
can be run both over IB (driver RDMA's a scatterlist to the RDS module)
or over TCP (TCP passes an sk_buff to the RDS module).

This patchset uses exiting socket filter infrastructure and extend it
with new eBPF program type that deals with struct scatterlist.
Existing bpf helper bpf_msg_pull_data() is used to inspect packet data
that are in form struct scatterlist. For RDS, the integrated approach
treats the scatterlist as the common denominator, and allows the
application to write a filter for processing a scatterlist.


Details:
Patch 1 adds new eBPF prog type BPF_PROG_TYPE_SOCKET_SG_FILTER which
uses the existing socket filter infrastructure for bpf program attach
and load. eBPF program of type BPF_PROG_TYPE_SOCKET_SG_FILTER deals with
struct scatterlist as bpf context contrast to
BPF_PROG_TYPE_SOCKET_FILTER which deals with struct skb. This new eBPF
program type allow socket filter to run on packet data that is in form
of struct scatterlist.

Patch 2 adds sg_filter_run() that runs BPF_PROG_TYPE_SOCKET_SG_FILTER.

Patch 3 fixes bpf_msg_pull_data() for the bugs that were found while
doing some experiment with different size of packets.

patch 4 allows rds_recv_incoming to invoke socket filter program which
deals with struct scatterlist.

Patch 5 adds socket filter eBPF sample program that uses patches 1 to 4.
The sample program opens an rds socket, attach ebpf program
(socksg i.e. BPF_PROG_TYPE_SOCKET_SG_FILTER) to rds socket and uses
bpf_msg_pull_data() helper to inspect RDS packet data. For a test,
current sample program only prints first few bytes of packet data.


Testing:
To confirm data accuracy and results, RDS packets of various sizes has
been tested with socksg program along with various start and end values
for bpf_msg_pull_data(). All such tests shows accurate results.

Thanks.

-Tushar



Tushar Dave (5):
  eBPF: Add new eBPF prog type BPF_PROG_TYPE_SOCKET_SG_FILTER
  ebpf: Add sg_filter_run()
  ebpf: fix bpf_msg_pull_data
  rds: invoke socket sg filter attached to rds socket
  ebpf: Add sample ebpf program for SOCKET_SG_FILTER

 include/linux/bpf_types.h      |   1 +
 include/linux/filter.h         |   8 +
 include/uapi/linux/bpf.h       |   7 +
 kernel/bpf/syscall.c           |   1 +
 kernel/bpf/verifier.c          |   1 +
 net/core/filter.c              | 140 +++++++++++++----
 net/rds/ib.c                   |   1 +
 net/rds/ib.h                   |   1 +
 net/rds/ib_recv.c              |  12 ++
 net/rds/rds.h                  |   2 +
 net/rds/recv.c                 |  17 +++
 net/rds/tcp.c                  |   2 +
 net/rds/tcp.h                  |   2 +
 net/rds/tcp_recv.c             |  38 +++++
 samples/bpf/Makefile           |   3 +
 samples/bpf/bpf_load.c         |  11 +-
 samples/bpf/rds_filter_kern.c  |  42 +++++
 samples/bpf/rds_filter_user.c  | 339 +++++++++++++++++++++++++++++++++++++++++
 tools/bpf/bpftool/prog.c       |   1 +
 tools/include/uapi/linux/bpf.h |   7 +
 tools/lib/bpf/libbpf.c         |   3 +
 tools/lib/bpf/libbpf.h         |   2 +
 22 files changed, 607 insertions(+), 34 deletions(-)
 create mode 100644 samples/bpf/rds_filter_kern.c
 create mode 100644 samples/bpf/rds_filter_user.c