vchan-socket-proxy: Ensure UNIX path NUL terminated

Check the socket path length to ensure sun_path is NUL terminated.

This was spotted by Citrix's Coverity.

Also use strcpy to avoid a warning "'__builtin_strncpy' specified bound
108 equals destination size [-Werror=stringop-truncation]" flagged by
gcc 10.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: Wei Liu <wl@xen.org>
Reviewed-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Release-acked-by: Paul Durrant <paul@xen.org>

tools/libvchan/vchan-socket-proxy.c

@@ -148,12 +148,18 @@ static int connect_socket(const char *path_or_fd) {
         return fd;
     }
 
+    if (strlen(path_or_fd) >= sizeof(addr.sun_path)) {
+        fprintf(stderr, "UNIX socket path \"%s\" too long (%zd >= %zd)\n",
+                path_or_fd, strlen(path_or_fd), sizeof(addr.sun_path));
+        return -1;
+    }
+
     fd = socket(AF_UNIX, SOCK_STREAM, 0);
     if (fd == -1)
         return -1;
 
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path));
+    strcpy(addr.sun_path, path_or_fd);
     if (connect(fd, (const struct sockaddr *)&addr, sizeof(addr)) == -1) {
         close(fd);
         return -1;
@@ -174,13 +180,19 @@ static int listen_socket(const char *path_or_fd) {
         return fd;
     }
 
+    if (strlen(path_or_fd) >= sizeof(addr.sun_path)) {
+        fprintf(stderr, "UNIX socket path \"%s\" too long (%zd >= %zd)\n",
+                path_or_fd, strlen(path_or_fd), sizeof(addr.sun_path));
+        return -1;
+    }
+
     /* if not a number, assume a socket path */
     fd = socket(AF_UNIX, SOCK_STREAM, 0);
     if (fd == -1)
         return -1;
 
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path));
+    strcpy(addr.sun_path, path_or_fd);
     if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) == -1) {
         close(fd);
         return -1;