feat(linux-sandbox): vendor bubblewrap and wire it with FFI (#10413)

## Summary

Vendor Bubblewrap into the repo and add minimal build plumbing in
`codex-linux-sandbox` to compile/link it.

## Why

We want to move Linux sandboxing toward Bubblewrap, but in a safe
two-step rollout:
1) vendoring/build setup (this PR),  
2) runtime integration (follow-up PR).

## Included

- Add `codex-rs/vendor/bubblewrap` sources.
- Add build-time FFI path in `codex-rs/linux-sandbox`.
- Update `build.rs` rerun tracking for vendored files.
- Small vendored compile warning fix (`sockaddr_nl` full init).

follow up in https://github.com/openai/codex/pull/9938

codex-rs/vendor/bubblewrap/network.c

@@ -0,0 +1,199 @@
+/* bubblewrap
+ * Copyright (C) 2016 Alexander Larsson
+ * SPDX-License-Identifier: LGPL-2.0-or-later
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "config.h"
+
+#include <arpa/inet.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <linux/loop.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+
+#include "utils.h"
+#include "network.h"
+
+static void *
+add_rta (struct nlmsghdr *header,
+         int              type,
+         size_t           size)
+{
+  struct rtattr *rta;
+  size_t rta_size = RTA_LENGTH (size);
+
+  rta = (struct rtattr *) ((char *) header + NLMSG_ALIGN (header->nlmsg_len));
+  rta->rta_type = type;
+  rta->rta_len = rta_size;
+
+  header->nlmsg_len = NLMSG_ALIGN (header->nlmsg_len) + rta_size;
+
+  return RTA_DATA (rta);
+}
+
+static int
+rtnl_send_request (int              rtnl_fd,
+                   struct nlmsghdr *header)
+{
+  struct sockaddr_nl dst_addr = { .nl_family = AF_NETLINK, .nl_pid = 0, .nl_groups = 0 };
+  ssize_t sent;
+
+  sent = TEMP_FAILURE_RETRY (sendto (rtnl_fd, (void *) header, header->nlmsg_len, 0,
+                                     (struct sockaddr *) &dst_addr, sizeof (dst_addr)));
+  if (sent < 0)
+    return -1;
+
+  return 0;
+}
+
+static int
+rtnl_read_reply (int          rtnl_fd,
+                 unsigned int seq_nr)
+{
+  char buffer[1024];
+  ssize_t received;
+  struct nlmsghdr *rheader;
+
+  while (1)
+    {
+      received = TEMP_FAILURE_RETRY (recv (rtnl_fd, buffer, sizeof (buffer), 0));
+      if (received < 0)
+        return -1;
+
+      rheader = (struct nlmsghdr *) buffer;
+      while (received >= NLMSG_HDRLEN)
+        {
+          if (rheader->nlmsg_seq != seq_nr)
+            return -1;
+          if ((pid_t)rheader->nlmsg_pid != getpid ())
+            return -1;
+          if (rheader->nlmsg_type == NLMSG_ERROR)
+            {
+              uint32_t *err = NLMSG_DATA (rheader);
+              if (*err == 0)
+                return 0;
+
+              return -1;
+            }
+          if (rheader->nlmsg_type == NLMSG_DONE)
+            return 0;
+
+          rheader = NLMSG_NEXT (rheader, received);
+        }
+    }
+}
+
+static int
+rtnl_do_request (int              rtnl_fd,
+                 struct nlmsghdr *header)
+{
+  if (rtnl_send_request (rtnl_fd, header) != 0)
+    return -1;
+
+  if (rtnl_read_reply (rtnl_fd, header->nlmsg_seq) != 0)
+    return -1;
+
+  return 0;
+}
+
+static struct nlmsghdr *
+rtnl_setup_request (char  *buffer,
+                    int    type,
+                    int    flags,
+                    size_t size)
+{
+  struct nlmsghdr *header;
+  size_t len = NLMSG_LENGTH (size);
+  static uint32_t counter = 0;
+
+  memset (buffer, 0, len);
+
+  header = (struct nlmsghdr *) buffer;
+  header->nlmsg_len = len;
+  header->nlmsg_type = type;
+  header->nlmsg_flags = flags | NLM_F_REQUEST;
+  header->nlmsg_seq = counter++;
+  header->nlmsg_pid = getpid ();
+
+  return header;
+}
+
+void
+loopback_setup (void)
+{
+  int r, if_loopback;
+  cleanup_fd int rtnl_fd = -1;
+  char buffer[1024];
+  struct sockaddr_nl src_addr = { .nl_family = AF_NETLINK, .nl_pid = 0, .nl_groups = 0 };
+  struct nlmsghdr *header;
+  struct ifaddrmsg *addmsg;
+  struct ifinfomsg *infomsg;
+  struct in_addr *ip_addr;
+
+  src_addr.nl_pid = getpid ();
+
+  if_loopback = (int) if_nametoindex ("lo");
+  if (if_loopback <= 0)
+    die_with_error ("loopback: Failed to look up lo");
+
+  rtnl_fd = socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
+  if (rtnl_fd < 0)
+    die_with_error ("loopback: Failed to create NETLINK_ROUTE socket");
+
+  r = bind (rtnl_fd, (struct sockaddr *) &src_addr, sizeof (src_addr));
+  if (r < 0)
+    die_with_error ("loopback: Failed to bind NETLINK_ROUTE socket");
+
+  header = rtnl_setup_request (buffer, RTM_NEWADDR,
+                               NLM_F_CREATE | NLM_F_EXCL | NLM_F_ACK,
+                               sizeof (struct ifaddrmsg));
+  addmsg = NLMSG_DATA (header);
+
+  addmsg->ifa_family = AF_INET;
+  addmsg->ifa_prefixlen = 8;
+  addmsg->ifa_flags = IFA_F_PERMANENT;
+  addmsg->ifa_scope = RT_SCOPE_HOST;
+  addmsg->ifa_index = if_loopback;
+
+  ip_addr = add_rta (header, IFA_LOCAL, sizeof (*ip_addr));
+  ip_addr->s_addr = htonl (INADDR_LOOPBACK);
+
+  ip_addr = add_rta (header, IFA_ADDRESS, sizeof (*ip_addr));
+  ip_addr->s_addr = htonl (INADDR_LOOPBACK);
+
+  assert (header->nlmsg_len < sizeof (buffer));
+
+  if (rtnl_do_request (rtnl_fd, header) != 0)
+    die_with_error ("loopback: Failed RTM_NEWADDR");
+
+  header = rtnl_setup_request (buffer, RTM_NEWLINK,
+                               NLM_F_ACK,
+                               sizeof (struct ifinfomsg));
+  infomsg = NLMSG_DATA (header);
+
+  infomsg->ifi_family = AF_UNSPEC;
+  infomsg->ifi_type = 0;
+  infomsg->ifi_index = if_loopback;
+  infomsg->ifi_flags = IFF_UP;
+  infomsg->ifi_change = IFF_UP;
+
+  assert (header->nlmsg_len < sizeof (buffer));
+
+  if (rtnl_do_request (rtnl_fd, header) != 0)
+    die_with_error ("loopback: Failed RTM_NEWLINK");
+}