[RFC PATCH 0/4] net/io_uring: pass a kernel pointer via optlen_t to proto[_ops].getsockopt()

[Stefan Metzmacher <metze@samba.org>]

The motivation for this is to remove the SOL_SOCKET limitation
from io_uring_cmd_getsockopt().

The reason for this limitation is that io_uring_cmd_getsockopt()
passes a kernel pointer as optlen to do_sock_getsockopt()
and can't reach the ops->getsockopt() path.

The first idea would be to change the optval and optlen arguments
to the protocol specific hooks also to sockptr_t, as that
is already used for setsockopt() and also by do_sock_getsockopt()
sk_getsockopt() and BPF_CGROUP_RUN_PROG_GETSOCKOPT().

But as Linus don't like 'sockptr_t' I used a different approach.

@Linus, would that optlen_t approach fit better for you?

Instead of passing the optlen as user or kernel pointer,
we only ever pass a kernel pointer and do the
translation from/to userspace in do_sock_getsockopt().

The simple solution would be to just remove the
'__user' from the int *optlen argument, but it
seems the compiler doesn't complain about
'__user' vs. without it, so instead I used
a helper struct in order to make sure everything
compiles with a typesafe change.

The patchset does the transformation in 3
easy to review steps:

1/4: introduces get_optlen(len, optlen) and put_optlen(len, optlen) helpers
     on top of the existing get_user(len, optlen) and put_user(len, optlen)
     usages.

2/4: introduces a simple optlen_t that just contains 'int __user *up;'
     that makes sure get_optlen and put_optlen get a typesafe optlen argument
     and they are the only functions looking at optlen.
     (The existing sockptr_t optlen code gets OPTLEN_SOCKPTR(optlen) passed)

3/4: The changes do_sock_getsockopt() to pass a kernel pointer instead
     of a __user pointer via optlen_t. This is a bit tricky as
     directly failing the copy_from_sockptr(&koptlen, optlen, sizeof(koptlen)
     with -EFAULT might change the uapi, as some getsockopt() hooks
     doesn't even touch optlen at all. And userspace could do something
     like this:

        feature_x_supported = true;
        ret = getsockopt(fd, level, optname, NULL, NULL);
        if (ret == -1 && errno == ENOTSUPP) {
            feature_x_supported = false;
        }

     And this should not give -EFAULT after the changes,
     so optlen.kp is passed down as NULL, so that -EFAULT is
     deferred to get_optlen() and put_optlen().

4/4: Removes the SOL_SOCKET restriction for io-uring.

This patchset doesn't touch any existing getsockopt() that
was already converted to sockptr_t optlen, that's something
for a later cleanup.

Link: https://lore.kernel.org/io-uring/86b1dce5-4bb4-4a0b-9cff-e72f488bf57d@samba.org/T/#t
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Stefan Metzmacher (4):
  net: introduce get_optlen() and put_optlen() helpers
  net: pass 'optlen_t' to proto[ops].getsockopt() hooks
  net: pass a kernel pointer via 'optlen_t' to proto[ops].getsockopt()
    hooks
  io_uring: let io_uring_cmd_getsockopt() allow level other than
    SOL_SOCKET

 drivers/isdn/mISDN/socket.c                   |   4 +-
 .../chelsio/inline_crypto/chtls/chtls_main.c  |   4 +-
 include/linux/net.h                           |   2 +-
 include/linux/sockptr.h                       |  41 ++++
 include/net/inet_connection_sock.h            |   2 +-
 include/net/ip.h                              |   2 +-
 include/net/ipv6.h                            |   2 +-
 include/net/sctp/structs.h                    |   2 +-
 include/net/sock.h                            |   4 +-
 include/net/tcp.h                             |   2 +-
 include/net/udp.h                             |   2 +-
 io_uring/uring_cmd.c                          |   3 -
 net/atm/common.c                              |   4 +-
 net/atm/common.h                              |   2 +-
 net/atm/pvc.c                                 |   2 +-
 net/atm/svc.c                                 |   4 +-
 net/ax25/af_ax25.c                            |   6 +-
 net/bluetooth/hci_sock.c                      |   6 +-
 net/bluetooth/iso.c                           |   6 +-
 net/bluetooth/l2cap_sock.c                    |   8 +-
 net/bluetooth/rfcomm/sock.c                   |   8 +-
 net/bluetooth/sco.c                           |  10 +-
 net/can/isotp.c                               |   6 +-
 net/can/j1939/socket.c                        |   6 +-
 net/can/raw.c                                 |  14 +-
 net/core/sock.c                               |   2 +-
 net/dccp/ccid.c                               |   4 +-
 net/dccp/ccid.h                               |  10 +-
 net/dccp/ccids/ccid3.c                        |   8 +-
 net/dccp/dccp.h                               |   2 +-
 net/dccp/proto.c                              |  12 +-
 net/ieee802154/socket.c                       |   8 +-
 net/ipv4/ip_sockglue.c                        |   8 +-
 net/ipv4/raw.c                                |  10 +-
 net/ipv4/tcp.c                                |   4 +-
 net/ipv4/udp.c                                |   8 +-
 net/ipv4/udp_impl.h                           |   2 +-
 net/ipv6/ipv6_sockglue.c                      |   8 +-
 net/ipv6/raw.c                                |  14 +-
 net/ipv6/udp.c                                |   2 +-
 net/ipv6/udp_impl.h                           |   2 +-
 net/iucv/af_iucv.c                            |   6 +-
 net/kcm/kcmsock.c                             |   6 +-
 net/l2tp/l2tp_ppp.c                           |   6 +-
 net/llc/af_llc.c                              |   6 +-
 net/mctp/af_mctp.c                            |   4 +-
 net/mptcp/protocol.h                          |   2 +-
 net/mptcp/sockopt.c                           |  48 ++--
 net/netlink/af_netlink.c                      |   8 +-
 net/netrom/af_netrom.c                        |   6 +-
 net/nfc/llcp_sock.c                           |   6 +-
 net/packet/af_packet.c                        |   6 +-
 net/phonet/pep.c                              |   6 +-
 net/rds/af_rds.c                              |   8 +-
 net/rds/info.c                                |   6 +-
 net/rds/info.h                                |   2 +-
 net/rose/af_rose.c                            |   6 +-
 net/rxrpc/af_rxrpc.c                          |   6 +-
 net/sctp/socket.c                             | 220 +++++++++---------
 net/smc/af_smc.c                              |   8 +-
 net/smc/smc.h                                 |   2 +-
 net/socket.c                                  |  34 ++-
 net/tipc/socket.c                             |   8 +-
 net/tls/tls_main.c                            |  18 +-
 net/vmw_vsock/af_vsock.c                      |   6 +-
 net/x25/af_x25.c                              |   6 +-
 net/xdp/xsk.c                                 |  10 +-
 67 files changed, 387 insertions(+), 319 deletions(-)

-- 
2.34.1