[PATCH 2/4] io_uring/cmd: Introduce SOCKET_URING_OP_GETSOCKOPT

[Breno Leitao <leitao@debian.org>]

Add support for getsockopt command (SOCKET_URING_OP_GETSOCKOPT), where
level is SOL_SOCKET. This is leveraging the sockptr_t infrastructure,
where a sockptr_t is either userspace or kernel space, and handled as
such.

Function io_uring_cmd_getsockopt() is inspired by __sys_getsockopt().

Differently from the getsockopt(2), the optlen field is not a userspace
pointers. In getsockopt(2), userspace provides optlen pointer, which is
overwritten by the kernel.  In this implementation, userspace passes a
u32, and the new value is returned in cqe->res. I.e., optlen is not a
pointer.

Important to say that userspace needs to keep the pointer alive until
the CQE is completed.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/uapi/linux/io_uring.h |  7 ++++++
 io_uring/uring_cmd.c          | 43 +++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 9fc7195f25df..8152151080db 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -43,6 +43,10 @@ struct io_uring_sqe {
 	union {
 		__u64	addr;	/* pointer to buffer or iovecs */
 		__u64	splice_off_in;
+		struct {
+			__u32	level;
+			__u32	optname;
+		};
 	};
 	__u32	len;		/* buffer size or number of iovecs */
 	union {
@@ -79,6 +83,7 @@ struct io_uring_sqe {
 	union {
 		__s32	splice_fd_in;
 		__u32	file_index;
+		__u32	optlen;
 		struct {
 			__u16	addr_len;
 			__u16	__pad3[1];
@@ -89,6 +94,7 @@ struct io_uring_sqe {
 			__u64	addr3;
 			__u64	__pad2[1];
 		};
+		__u64	optval;
 		/*
 		 * If the ring is initialized with IORING_SETUP_SQE128, then
 		 * this field is used for 80 bytes of arbitrary command data
@@ -729,6 +735,7 @@ struct io_uring_recvmsg_out {
 enum {
 	SOCKET_URING_OP_SIOCINQ		= 0,
 	SOCKET_URING_OP_SIOCOUTQ,
+	SOCKET_URING_OP_GETSOCKOPT,
 };
 
 #ifdef __cplusplus
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 8e7a03c1b20e..16c857cbf3b0 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -166,6 +166,47 @@ int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed);
 
+static inline int io_uring_cmd_getsockopt(struct socket *sock,
+					  struct io_uring_cmd *cmd)
+{
+	void __user *optval = u64_to_user_ptr(READ_ONCE(cmd->sqe->optval));
+	int optname = READ_ONCE(cmd->sqe->optname);
+	int optlen = READ_ONCE(cmd->sqe->optlen);
+	int level = READ_ONCE(cmd->sqe->level);
+	void *koptval;
+	int err;
+
+	err = security_socket_getsockopt(sock, level, optname);
+	if (err)
+		return err;
+
+	koptval = kmalloc(optlen, GFP_KERNEL);
+	if (!koptval)
+		return -ENOMEM;
+
+	err = copy_from_user(koptval, optval, optlen);
+	if (err)
+		goto fail;
+
+	err = -EOPNOTSUPP;
+	if (level == SOL_SOCKET) {
+		err = sk_getsockopt(sock->sk, level, optname,
+				    KERNEL_SOCKPTR(koptval),
+				    KERNEL_SOCKPTR(&optlen));
+		if (err)
+			goto fail;
+	}
+
+	err = copy_to_user(optval, koptval, optlen);
+
+fail:
+	kfree(koptval);
+	if (err)
+		return err;
+	else
+		return optlen;
+}
+
 int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
 {
 	struct socket *sock = cmd->file->private_data;
@@ -187,6 +228,8 @@ int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
 		if (ret)
 			return ret;
 		return arg;
+	case SOCKET_URING_OP_GETSOCKOPT:
+		return io_uring_cmd_getsockopt(sock, cmd);
 	default:
 		return -EOPNOTSUPP;
 	}
-- 
2.34.1