luad

commit a820bbf9330bc46238b6d284a90e8ac88f9691de
parent 7e123822485df1e01abf2a698f10b21540f4c24e
Author: Daniel Barlow <dan@telent.net>
Date:   Tue, 19 May 2026 21:50:02 +0100

verify we get exactly 3 fds from client

Diffstat:
M
luad.c
 | 
31
+++++++++++++++++++++++++++++--

1 file changed, 29 insertions(+), 2 deletions(-)
diff --git a/luad.c b/luad.c
@@ -55,16 +55,43 @@ int * fds_from_msg(struct msghdr *msg, int * peer_fds) {
     // * we expect three fds
     // * if we get some number other than three, we should
     //   close all of them and return NULL because someone is up to no good
+    int i = 0;
+    peer_fds[0] = -1;
+    peer_fds[1] = -1;
+    peer_fds[2] = -1;
 
     for (struct cmsghdr* cmsg = CMSG_FIRSTHDR(msg);
          cmsg != NULL;
          cmsg = CMSG_NXTHDR(msg, cmsg)) {
         if(cmsg->cmsg_level == SOL_SOCKET &&
            cmsg->cmsg_type == SCM_RIGHTS) {
-            memcpy(peer_fds, CMSG_DATA(cmsg), 3 * sizeof(int));
+            int passed_fd_count = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof (int);
+            if(i <= 3) {
+                memcpy(&peer_fds[i], CMSG_DATA(cmsg), passed_fd_count * sizeof(int));
+
+            } else {
+                int * reject_fds = (int *) CMSG_DATA(cmsg);
+                for(int fd = 0; fd < passed_fd_count; fd++) {
+                    close(reject_fds[fd]);
+                }
+            }
+            i += passed_fd_count;
         }
     }
-    return peer_fds;
+    if(i != 3) {
+        /* if the peer sent too many fds, we closed the excess ones
+         * in the reject_fds clause above and now we'll close the
+         * first three.
+         * if they sent too few, we'll close whatever they sent
+         */
+
+        if(peer_fds[0] >=0) close(peer_fds[0]);
+        if(peer_fds[1] >=0) close(peer_fds[1]);
+        if(peer_fds[2] >=0) close(peer_fds[2]);
+        return NULL;
+    } else {
+        return peer_fds;
+    }
 }
 
 int start_lua_child(lua_State *L,