From: Florian Westphal <fw@strlen.de>

earlier patch added IP_TOS setsockopt support, this allows to get
the value set by earlier setsockopt.

Extends mptcp_put_int_option to handle u8 input/output by
adding required cast.

Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
---
 net/mptcp/sockopt.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 11cda8629993..44e0a37c567c 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1053,15 +1053,24 @@ static int mptcp_put_int_option(struct mptcp_sock *msk, char __user *optval,
 
 	if (get_user(len, optlen))
 		return -EFAULT;
-
-	len = min_t(unsigned int, len, sizeof(int));
 	if (len < 0)
 		return -EINVAL;
 
-	if (put_user(len, optlen))
-		return -EFAULT;
-	if (copy_to_user(optval, &val, len))
-		return -EFAULT;
+	if (len < sizeof(int) && len > 0 && val >= 0 && val <= 255) {
+		unsigned char ucval = (unsigned char)val;
+
+		len = 1;
+		if (put_user(len, optlen))
+			return -EFAULT;
+		if (copy_to_user(optval, &ucval, 1))
+			return -EFAULT;
+	} else {
+		len = min_t(unsigned int, len, sizeof(int));
+		if (put_user(len, optlen))
+			return -EFAULT;
+		if (copy_to_user(optval, &val, len))
+			return -EFAULT;
+	}
 
 	return 0;
 }
@@ -1082,6 +1091,19 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 	return -EOPNOTSUPP;
 }
 
+static int mptcp_getsockopt_v4(struct mptcp_sock *msk, int optname,
+			       char __user *optval, int __user *optlen)
+{
+	struct sock *sk = (void *)msk;
+
+	switch (optname) {
+	case IP_TOS:
+		return mptcp_put_int_option(msk, optval, optlen, inet_sk(sk)->tos);
+	}
+
+	return -EOPNOTSUPP;
+}
+
 static int mptcp_getsockopt_sol_mptcp(struct mptcp_sock *msk, int optname,
 				      char __user *optval, int __user *optlen)
 {
@@ -1117,6 +1139,8 @@ int mptcp_getsockopt(struct sock *sk, int level, int optname,
 	if (ssk)
 		return tcp_getsockopt(ssk, level, optname, optval, option);
 
+	if (level == SOL_IP)
+		return mptcp_getsockopt_v4(msk, optname, optval, option);
 	if (level == SOL_TCP)
 		return mptcp_getsockopt_sol_tcp(msk, optname, optval, option);
 	if (level == SOL_MPTCP)
-- 
2.34.1

On Fri,  3 Dec 2021 14:35:37 -0800 Mat Martineau wrote:
>  	if (get_user(len, optlen))
>  		return -EFAULT;
> -
> -	len = min_t(unsigned int, len, sizeof(int));

Ah, there's the min() gone. Okay.

>  	if (len < 0)
>  		return -EINVAL;