Subject: Re: [PATCH v3 8/9] io_uring/cmd: BPF hook for getsockopt cmd

From: Breno Leitao <[email-masked]>
Date: Fri, 25 Aug 2023 09:53:58 -0700

On Mon, Aug 21, 2023 at 01:25:25PM -0700, Martin KaFai Lau wrote:
> On 8/17/23 12:08 PM, Gabriel Krisman Bertazi wrote:
> > Shouldn't you call sock->ops->getsockopt for level!=SOL_SOCKET prior to
> > running the hook?  Before this patch, it would bail out with EOPNOTSUPP,
> > but now the bpf hook gets called even for level!=SOL_SOCKET, which
> > doesn't fit __sys_getsockopt. Am I misreading the code?
> I agree it should not call into bpf if the io_uring cannot support non
> SOL_SOCKET optnames. Otherwise, the bpf prog will get different optval and
> optlen when running in _sys_getsockopt vs io_uring getsockopt (e.g. in
> regular _sys_getsockopt(SOL_TCP), bpf expects the optval returned from
> tcp_getsockopt).
> 
> I think __sys_getsockopt can also be refactored similar to __sys_setsockopt
> in patch 3. Yes, for non SOL_SOCKET it only supports __user *optval and
> __user *optlen but may be a WARN_ON_ONCE/BUG_ON(sockpt_is_kernel(optval))
> can be added before calling ops->getsockopt()? Then this details can be
> hidden away from the io_uring.

Right, I've spent some time thinking about it, and this could be done.
This is a draft I have. Is it what you had in mind?

--

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 5e3419eb267a..e39743f4ce5e 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -378,7 +378,7 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
 ({									       \
 	int __ret = 0;							       \
 	if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))			       \
-		get_user(__ret, optlen);				       \
+		copy_from_sockptr(&__ret, optlen, sizeof(int));		       \
 	__ret;								       \
 })
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 2a0324275347..24ea1719fd02 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1855,6 +1855,8 @@ int sock_setsockopt(struct socket *sock, int level, int op,
 		    sockptr_t optval, unsigned int optlen);
 int do_sock_setsockopt(struct socket *sock, bool compat, int level,
 		       int optname, sockptr_t optval, int optlen);
+int do_sock_getsockopt(struct socket *sock, bool compat, int level,
+		       int optname, sockptr_t optval, sockptr_t optlen);
 
 int sk_getsockopt(struct sock *sk, int level, int optname,
 		  sockptr_t optval, sockptr_t optlen);
diff --git a/net/core/sock.c b/net/core/sock.c
index 9370fd50aa2c..2a5f30f14f5c 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1997,14 +1997,6 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 	return 0;
 }
 
-int sock_getsockopt(struct socket *sock, int level, int optname,
-		    char __user *optval, int __user *optlen)
-{
-	return sk_getsockopt(sock->sk, level, optname,
-			     USER_SOCKPTR(optval),
-			     USER_SOCKPTR(optlen));
-}
-
 /*
  * Initialize an sk_lock.
  *
diff --git a/net/socket.c b/net/socket.c
index b5e4398a6b4d..f0d6b6b1f75e 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2290,6 +2290,40 @@ SYSCALL_DEFINE5(setsockopt, int, fd, int, level, int, optname,
 INDIRECT_CALLABLE_DECLARE(bool tcp_bpf_bypass_getsockopt(int level,
 							 int optname));
 
+int do_sock_getsockopt(struct socket *sock, bool compat, int level,
+		       int optname, sockptr_t optval, sockptr_t optlen)
+{
+	int max_optlen __maybe_unused;
+	int err;
+
+	err = security_socket_getsockopt(sock, level, optname);
+	if (err)
+		return err;
+
+	if (level == SOL_SOCKET) {
+		err = sk_getsockopt(sock->sk, level, optname, optval, optlen);
+	} else if (unlikely(!sock->ops->getsockopt)) {
+		err = -EOPNOTSUPP;
+	} else {
+		if (WARN_ONCE(optval.is_kernel || optlen.is_kernel,
+			      "Invalid argument type"))
+			return -EOPNOTSUPP;
+
+		err = sock->ops->getsockopt(sock, level, optname, optval.user,
+					    optlen.user);
+	}
+
+	if (!compat) {
+		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
+		err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname,
+						     optval, optlen, max_optlen,
+						     err);
+	}
+
+	return err;
+}
+EXPORT_SYMBOL(do_sock_getsockopt);
+
 /*
  *	Get a socket option. Because we don't know the option lengths we have
  *	to pass a user mode parameter for the protocols to sort out.
@@ -2297,35 +2331,17 @@ INDIRECT_CALLABLE_DECLARE(bool tcp_bpf_bypass_getsockopt(int level,
 int __sys_getsockopt(int fd, int level, int optname, char __user *optval,
 		int __user *optlen)
 {
-	int max_optlen __maybe_unused;
 	int err, fput_needed;
+	bool compat = in_compat_syscall();
 	struct socket *sock;
 
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (!sock)
 		return err;
 
-	err = security_socket_getsockopt(sock, level, optname);
-	if (err)
-		goto out_put;
-
-	if (!in_compat_syscall())
-		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
-
-	if (level == SOL_SOCKET)
-		err = sock_getsockopt(sock, level, optname, optval, optlen);
-	else if (unlikely(!sock->ops->getsockopt))
-		err = -EOPNOTSUPP;
-	else
-		err = sock->ops->getsockopt(sock, level, optname, optval,
-					    optlen);
+	err = do_sock_getsockopt(sock, compat, level, optname,
+				 USER_SOCKPTR(optval), USER_SOCKPTR(optlen));
 
-	if (!in_compat_syscall())
-		err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname,
-						     USER_SOCKPTR(optval),
-						     USER_SOCKPTR(optlen),
-						     max_optlen, err);
-out_put:
 	fput_light(sock->file, fput_needed);
 	return err;
 }