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

Stefan Metzmacher
2025-03-31T20:11:55Z

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(-)

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2.34.1