From 2cbcde19f62970a8da308d5b128b2b2d7c725077 Mon Sep 17 00:00:00 2001
From: dec05eba <dec05eba@protonmail.com>
Date: Sat, 18 Nov 2023 13:55:27 +0100
Subject: Properly send socketpair fd to kms server

---
 kms/client/kms_client.c | 26 ++++++++++++++++++++++----
 kms/server/kms_server.c | 45 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 59 insertions(+), 12 deletions(-)

diff --git a/kms/client/kms_client.c b/kms/client/kms_client.c
index 3e60c63..8e1dafb 100644
--- a/kms/client/kms_client.c
+++ b/kms/client/kms_client.c
@@ -53,11 +53,29 @@ static int send_msg_to_server(int server_fd, gsr_kms_request *request) {
     iov.iov_base = request;
     iov.iov_len = sizeof(*request);
 
-    struct msghdr request_message = {0};
-    request_message.msg_iov = &iov;
-    request_message.msg_iovlen = 1;
+    struct msghdr response_message = {0};
+    response_message.msg_iov = &iov;
+    response_message.msg_iovlen = 1;
+
+    char cmsgbuf[CMSG_SPACE(sizeof(int) * 1)];
+    memset(cmsgbuf, 0, sizeof(cmsgbuf));
+
+    if(request->new_connection_fd > 0) {
+        response_message.msg_control = cmsgbuf;
+        response_message.msg_controllen = sizeof(cmsgbuf);
+
+        struct cmsghdr *cmsg = CMSG_FIRSTHDR(&response_message);
+        cmsg->cmsg_level = SOL_SOCKET;
+        cmsg->cmsg_type = SCM_RIGHTS;
+        cmsg->cmsg_len = CMSG_LEN(sizeof(int) * 1);
+
+        int *fds = (int*)CMSG_DATA(cmsg);
+        fds[0] = request->new_connection_fd;
+
+        response_message.msg_controllen = cmsg->cmsg_len;
+    }
 
-    return sendmsg(server_fd, &request_message, 0);
+    return sendmsg(server_fd, &response_message, 0);
 }
 
 static int recv_msg_from_server(int server_fd, gsr_kms_response *response) {
diff --git a/kms/server/kms_server.c b/kms/server/kms_server.c
index 39ce446..fbd101e 100644
--- a/kms/server/kms_server.c
+++ b/kms/server/kms_server.c
@@ -68,6 +68,40 @@ static int send_msg_to_client(int client_fd, gsr_kms_response *response) {
     return sendmsg(client_fd, &response_message, 0);
 }
 
+static int recv_msg_from_client(int client_fd, gsr_kms_request *request) {
+    struct iovec iov;
+    iov.iov_base = request;
+    iov.iov_len = sizeof(*request);
+
+    struct msghdr response_message = {0};
+    response_message.msg_iov = &iov;
+    response_message.msg_iovlen = 1;
+
+    char cmsgbuf[CMSG_SPACE(sizeof(int) * 1)];
+    memset(cmsgbuf, 0, sizeof(cmsgbuf));
+    response_message.msg_control = cmsgbuf;
+    response_message.msg_controllen = sizeof(cmsgbuf);
+
+    int res = recvmsg(client_fd, &response_message, MSG_WAITALL);
+    if(res <= 0)
+        return res;
+
+    if(request->new_connection_fd > 0) {
+        struct cmsghdr *cmsg = CMSG_FIRSTHDR(&response_message);
+        if(cmsg) {
+            int *fds = (int*)CMSG_DATA(cmsg);
+            request->new_connection_fd = fds[0];
+        } else {
+            if(request->new_connection_fd > 0) {
+                close(request->new_connection_fd);
+                request->new_connection_fd = 0;
+            }
+        }
+    }
+
+    return res;
+}
+
 static bool connector_get_property_by_name(int drmfd, drmModeConnectorPtr props, const char *name, uint64_t *result) {
     for(int i = 0; i < props->count_props; ++i) {
         drmModePropertyPtr prop = drmModeGetProperty(drmfd, props->props[i]);
@@ -410,14 +444,9 @@ int main(int argc, char **argv) {
         gsr_kms_request request;
         request.version = 0;
         request.type = -1;
-        struct iovec iov;
-        iov.iov_base = &request;
-        iov.iov_len = sizeof(request);
-
-        struct msghdr request_message = {0};
-        request_message.msg_iov = &iov;
-        request_message.msg_iovlen = 1;
-        const int recv_res = recvmsg(socket_fd, &request_message, MSG_WAITALL);
+        request.new_connection_fd = 0;
+
+        const int recv_res = recv_msg_from_client(socket_fd, &request);
         if(recv_res == 0) {
             fprintf(stderr, "kms server info: kms client shutdown, shutting down the server\n");
             res = 3;
-- 
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