[PATCH 0/5] Return fds from privileged sockhash/sockmap lookup

[Lorenz Bauer <lmb@cloudflare.com>]

We want to use sockhash and sockmap to build the control plane for
our upcoming BPF socket dispatch work. We realised that it's
difficult to resize or otherwise rebuild these maps if needed,
because there is no way to get at their contents. This patch set
allows a privileged user to retrieve fds from these map types,
which removes this obstacle.

The approach here is different than that of program arrays and
nested maps, which return an ID that can be turned into an fd
using the BPF_*_GET_FD_BY_ID syscall. Sockets have IDs in the
form of cookies, however there seems to be no way to go from
a socket cookie to struct socket or struct file. Hence we
return an fd directly.

If unprivileged access is desired, the user can create the map
with value_size = 8, which makes lookup return the socket
cookie. It would be nicer if this behaviour was controllable at
the time of calling bpf_map_lookup_elem, but I've not found
a good solution for this.

Patches 1-3 do a bit of clean up, but I'm happy to drop them
if they don't make sense. Patch 4-5 are the interesting bit.

Lorenz Bauer (5):
  bpf: add map_copy_value hook
  bpf: convert queue and stack map to map_copy_value
  bpf: convert sock map and hash to map_copy_value
  bpf: sockmap, sockhash: return file descriptors from privileged lookup
  bpf: sockmap, sockhash: test looking up fds

 include/linux/bpf-cgroup.h                    |  5 --
 include/linux/bpf.h                           | 21 +-----
 include/linux/bpf_types.h                     |  2 +-
 kernel/bpf/arraymap.c                         | 13 +++-
 kernel/bpf/bpf_struct_ops.c                   |  7 +-
 kernel/bpf/hashtab.c                          | 10 ++-
 kernel/bpf/local_storage.c                    | 14 +++-
 kernel/bpf/queue_stack_maps.c                 | 18 +++++
 kernel/bpf/reuseport_array.c                  |  5 +-
 kernel/bpf/syscall.c                          | 23 +------
 net/core/sock_map.c                           | 67 ++++++++++++++-----
 .../selftests/bpf/prog_tests/sockmap_listen.c | 26 +++++--
 12 files changed, 130 insertions(+), 81 deletions(-)

-- 
2.20.1