Introduce netns API
Write a new API and implementation to manage network namespace related
operations.
This will be used by the upcoming tundev module.
Change-Id: I0f2fba2fa42250a07211a7b7f479498f27c529da
diff --git a/src/core/netns.c b/src/core/netns.c
new file mode 100644
index 0000000..56b0c3a
--- /dev/null
+++ b/src/core/netns.c
@@ -0,0 +1,208 @@
+
+/* Network namespace convenience functions
+ * (C) 2023 by sysmocom - s.m.f.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ */
+
+#include "config.h"
+
+/*! \addtogroup netns
+ * @{
+ * Network namespace convenience functions
+ *
+ * \file netns.c */
+
+#if defined(__linux__)
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sched.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/mount.h>
+#include <sys/param.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/netns.h>
+
+#define NETNS_PREFIX_PATH "/var/run/netns"
+#define NETNS_CURRENT_PATH "/proc/self/ns/net"
+
+/*! Open a file descriptor for the current network namespace.
+ * \returns fd of the current network namespace on success; negative in case of error
+ */
+static int netns_open_current_fd(void)
+{
+ int fd;
+ /* store the default namespace for later reference */
+ if ((fd = open(NETNS_CURRENT_PATH, O_RDONLY)) < 0)
+ return -errno;
+ return fd;
+}
+
+/*! switch to a (non-default) namespace, store existing signal mask in oldmask.
+ * \param[in] nsfd file descriptor representing the namespace to which we shall switch
+ * \param[out] state caller-provided memory location to which state of previous netns is stored
+ * \returns 0 on success; negative on error */
+int osmo_netns_switch_enter(int nsfd, struct osmo_netns_switch_state *state)
+{
+ sigset_t intmask;
+ int rc;
+
+ state->prev_nsfd = -1;
+
+ if (sigfillset(&intmask) < 0)
+ return -errno;
+ if ((rc = sigprocmask(SIG_BLOCK, &intmask, &state->prev_sigmask)) != 0)
+ return -rc;
+ state->prev_nsfd = netns_open_current_fd();
+
+ if (setns(nsfd, CLONE_NEWNET) < 0) {
+ /* restore old mask if we couldn't switch the netns */
+ sigprocmask(SIG_SETMASK, &state->prev_sigmask, NULL);
+ close(state->prev_nsfd);
+ state->prev_nsfd = -1;
+ return -errno;
+ }
+ return 0;
+}
+
+/*! switch back to the previous namespace, restoring signal mask.
+ * \param[in] state information about previous netns, filled by osmo_netns_switch_enter()
+ * \returns 0 on successs; negative on error */
+int osmo_netns_switch_exit(struct osmo_netns_switch_state *state)
+{
+ if (state->prev_nsfd < 0)
+ return -EINVAL;
+
+ int rc;
+ if (setns(state->prev_nsfd, CLONE_NEWNET) < 0)
+ return -errno;
+
+ close(state->prev_nsfd);
+ state->prev_nsfd = -1;
+
+ if ((rc = sigprocmask(SIG_SETMASK, &state->prev_sigmask, NULL)) != 0)
+ return -rc;
+ return 0;
+}
+
+static int create_netns(const char *name)
+{
+ char path[MAXPATHLEN];
+ sigset_t intmask, oldmask;
+ int fd, prev_nsfd;
+ int rc, rc2;
+
+ /* create /var/run/netns, if it doesn't exist already */
+ rc = mkdir(NETNS_PREFIX_PATH, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
+ if (rc < 0 && errno != EEXIST)
+ return rc;
+
+ /* create /var/run/netns/[name], if it doesn't exist already */
+ rc = snprintf(path, sizeof(path), "%s/%s", NETNS_PREFIX_PATH, name);
+ if (rc >= sizeof(path))
+ return -ENAMETOOLONG;
+ fd = open(path, O_RDONLY|O_CREAT|O_EXCL, 0);
+ if (fd < 0)
+ return -errno;
+ if (close(fd) < 0)
+ return -errno;
+
+ /* mask off all signals, store old signal mask */
+ if (sigfillset(&intmask) < 0)
+ return -errno;
+ if ((rc = sigprocmask(SIG_BLOCK, &intmask, &oldmask)) != 0)
+ return -rc;
+
+ prev_nsfd = netns_open_current_fd();
+ if (prev_nsfd < 0)
+ return prev_nsfd;
+
+ /* create a new network namespace */
+ if (unshare(CLONE_NEWNET) < 0) {
+ rc = -errno;
+ goto restore_sigmask;
+ }
+ if (mount(NETNS_CURRENT_PATH, path, "none", MS_BIND, NULL) < 0) {
+ rc = -errno;
+ goto restore_sigmask;
+ }
+
+ /* switch back to previous namespace */
+ if (setns(prev_nsfd, CLONE_NEWNET) < 0) {
+ rc = -errno;
+ goto restore_sigmask;
+ }
+
+restore_sigmask:
+ close(prev_nsfd);
+
+ /* restore process mask */
+ if ((rc2 = sigprocmask(SIG_SETMASK, &oldmask, NULL)) != 0)
+ return -rc2;
+
+ /* might have been set above in case mount fails */
+ if (rc < 0)
+ return rc;
+
+ /* finally, open the created namespace file descriptor from previous ns */
+ if ((fd = open(path, O_RDONLY)) < 0)
+ return -errno;
+
+ return fd;
+}
+
+/*! Open a file descriptor for the network namespace with provided name.
+ * Creates /var/run/netns/ directory if it doesn't exist already.
+ * \param[in] name Name of the network namespace (in /var/run/netns/)
+ * \returns File descriptor of network namespace; negative in case of error
+ */
+int osmo_netns_open_fd(const char *name)
+{
+ int rc;
+ int fd;
+ char path[MAXPATHLEN];
+
+ /* path = /var/run/netns/[name] */
+ rc = snprintf(path, sizeof(path), "%s/%s", NETNS_PREFIX_PATH, name);
+ if (rc >= sizeof(path))
+ return -ENAMETOOLONG;
+
+ /* If netns already exists, simply open it: */
+ fd = open(path, O_RDONLY);
+ if (fd >= 0)
+ return fd;
+
+ /* The netns doesn't exist yet, let's create it: */
+ fd = create_netns(name);
+ return fd;
+}
+
+#endif /* defined(__linux__) */
+
+/*! @} */