liblxc_la_SOURCES += ../include/strlcat.c ../include/strlcat.h
endif
-if !HAVE_GETGRGID_R
-liblxc_la_SOURCES += ../include/getgrgid_r.c ../include/getgrgid_r.h
-endif
-
-AM_CFLAGS=-DLXCROOTFSMOUNT=\"$(LXCROOTFSMOUNT)\" \
- -DLXCPATH=\"$(LXCPATH)\" \
- -DLXC_GLOBAL_CONF=\"$(LXC_GLOBAL_CONF)\" \
- -DLXCINITDIR=\"$(LXCINITDIR)\" \
- -DLIBEXECDIR=\"$(LIBEXECDIR)\" \
- -DLXCTEMPLATEDIR=\"$(LXCTEMPLATEDIR)\" \
- -DLXCTEMPLATECONFIG=\"$(LXCTEMPLATECONFIG)\" \
- -DLOGPATH=\"$(LOGPATH)\" \
- -DLXC_DEFAULT_CONFIG=\"$(LXC_DEFAULT_CONFIG)\" \
- -DLXC_USERNIC_DB=\"$(LXC_USERNIC_DB)\" \
- -DLXC_USERNIC_CONF=\"$(LXC_USERNIC_CONF)\" \
- -DDEFAULT_CGROUP_PATTERN=\"$(DEFAULT_CGROUP_PATTERN)\" \
- -DRUNTIME_PATH=\"$(RUNTIME_PATH)\" \
- -DSBINDIR=\"$(SBINDIR)\" \
- -I $(top_srcdir)/src \
- -I $(top_srcdir)/src/lxc \
- -I $(top_srcdir)/src/lxc/storage \
- -I $(top_srcdir)/src/lxc/cgroups
+if ENFORCE_MEMFD_REXEC
+liblxc_la_SOURCES += rexec.c
+endif
+
+AM_CFLAGS = -DLXCROOTFSMOUNT=\"$(LXCROOTFSMOUNT)\" \
+ -DLXCPATH=\"$(LXCPATH)\" \
+ -DLXC_GLOBAL_CONF=\"$(LXC_GLOBAL_CONF)\" \
+ -DLXCINITDIR=\"$(LXCINITDIR)\" \
+ -DLIBEXECDIR=\"$(LIBEXECDIR)\" \
+ -DLXCTEMPLATEDIR=\"$(LXCTEMPLATEDIR)\" \
+ -DLXCTEMPLATECONFIG=\"$(LXCTEMPLATECONFIG)\" \
+ -DLOGPATH=\"$(LOGPATH)\" \
+ -DLXC_DEFAULT_CONFIG=\"$(LXC_DEFAULT_CONFIG)\" \
+ -DLXC_USERNIC_DB=\"$(LXC_USERNIC_DB)\" \
+ -DLXC_USERNIC_CONF=\"$(LXC_USERNIC_CONF)\" \
+ -DDEFAULT_CGROUP_PATTERN=\"$(DEFAULT_CGROUP_PATTERN)\" \
+ -DRUNTIME_PATH=\"$(RUNTIME_PATH)\" \
+ -DSBINDIR=\"$(SBINDIR)\" \
+ -DAPPARMOR_CACHE_DIR=\"$(APPARMOR_CACHE_DIR)\" \
+ -I $(top_srcdir)/src \
+ -I $(top_srcdir)/src/lxc \
+ -I $(top_srcdir)/src/lxc/storage \
+ -I $(top_srcdir)/src/lxc/cgroups
if ENABLE_APPARMOR
AM_CFLAGS += -DHAVE_APPARMOR
--- /dev/null
+/* liblxcapi
+ *
+ * Copyright © 2019 Christian Brauner <christian.brauner@ubuntu.com>.
+ * Copyright © 2019 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE 1
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/sendfile.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "config.h"
+#include "utils.h"
+#include "syscall_wrappers.h"
+
+#define LXC_MEMFD_REXEC_SEALS \
+ (F_SEAL_SEAL | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
+
+static int push_vargs(char *data, int data_length, char ***output)
+{
+ int num = 0;
+ char *cur = data;
+
+ if (!data || *output)
+ return -1;
+
+ *output = must_realloc(NULL, sizeof(**output));
+
+ while (cur < data + data_length) {
+ num++;
+ *output = must_realloc(*output, (num + 1) * sizeof(**output));
+
+ (*output)[num - 1] = cur;
+ cur += strlen(cur) + 1;
+ }
+ (*output)[num] = NULL;
+ return num;
+}
+
+static char *file_to_buf(char *path, size_t *length)
+{
+ int fd;
+ char buf[PATH_MAX];
+ char *copy = NULL;
+
+ if (!length)
+ return NULL;
+
+ fd = open(path, O_RDONLY | O_CLOEXEC);
+ if (fd < 0)
+ return NULL;
+
+ *length = 0;
+ for (;;) {
+ int n;
+ char *old = copy;
+
+ n = lxc_read_nointr(fd, buf, sizeof(buf));
+ if (n < 0)
+ goto on_error;
+ if (!n)
+ break;
+
+ copy = must_realloc(old, (*length + n) * sizeof(*old));
+ memcpy(copy + *length, buf, n);
+ *length += n;
+ }
+
+ close(fd);
+ return copy;
+
+on_error:
+ close(fd);
+ free(copy);
+
+ return NULL;
+}
+
+static int parse_exec_params(char ***argv, char ***envp)
+{
+ int ret;
+ char *cmdline = NULL, *env = NULL;
+ size_t cmdline_size, env_size;
+
+ cmdline = file_to_buf("/proc/self/cmdline", &cmdline_size);
+ if (!cmdline)
+ goto on_error;
+
+ env = file_to_buf("/proc/self/environ", &env_size);
+ if (!env)
+ goto on_error;
+
+ ret = push_vargs(cmdline, cmdline_size, argv);
+ if (ret <= 0)
+ goto on_error;
+
+ ret = push_vargs(env, env_size, envp);
+ if (ret <= 0)
+ goto on_error;
+
+ return 0;
+
+on_error:
+ free(env);
+ free(cmdline);
+
+ return -1;
+}
+
+static int is_memfd(void)
+{
+ int fd, saved_errno, seals;
+
+ fd = open("/proc/self/exe", O_RDONLY | O_CLOEXEC);
+ if (fd < 0)
+ return -ENOTRECOVERABLE;
+
+ seals = fcntl(fd, F_GET_SEALS);
+ saved_errno = errno;
+ close(fd);
+ errno = saved_errno;
+ if (seals < 0)
+ return -EINVAL;
+
+ return seals == LXC_MEMFD_REXEC_SEALS;
+}
+
+/* Maximum number of bytes sendfile() is able to send in one go. */
+#define LXC_SENDFILE_MAX 0x7ffff000
+static ssize_t lxc_sendfile_nointr(int out_fd, int in_fd, off_t *offset, size_t count)
+{
+ ssize_t ret;
+
+again:
+ ret = sendfile(out_fd, in_fd, offset, count);
+ if (ret < 0) {
+ if (errno == EINTR)
+ goto again;
+
+ return -1;
+ }
+
+ return ret;
+}
+
+static void lxc_rexec_as_memfd(char **argv, char **envp, const char *memfd_name)
+{
+ int saved_errno;
+ ssize_t bytes_sent;
+ int fd = -1, memfd = -1;
+
+ memfd = memfd_create(memfd_name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
+ if (memfd < 0)
+ return;
+
+ fd = open("/proc/self/exe", O_RDONLY | O_CLOEXEC);
+ if (fd < 0)
+ goto on_error;
+
+ /* sendfile() handles up to 2GB. */
+ bytes_sent = lxc_sendfile_nointr(memfd, fd, NULL, LXC_SENDFILE_MAX);
+ saved_errno = errno;
+ close(fd);
+ errno = saved_errno;
+ if (bytes_sent < 0)
+ goto on_error;
+
+ if (fcntl(memfd, F_ADD_SEALS, LXC_MEMFD_REXEC_SEALS))
+ goto on_error;
+
+ fexecve(memfd, argv, envp);
+
+on_error:
+ saved_errno = errno;
+ close(memfd);
+ errno = saved_errno;
+}
+
+static int lxc_rexec(const char *memfd_name)
+{
+ int ret;
+ char **argv = NULL, **envp = NULL;
+
+ ret = is_memfd();
+ if (ret < 0 && ret == -ENOTRECOVERABLE) {
+ fprintf(stderr,
+ "%s - Failed to determine whether this is a memfd\n",
+ strerror(errno));
+ return -1;
+ } else if (ret > 0) {
+ return 0;
+ }
+
+ ret = parse_exec_params(&argv, &envp);
+ if (ret < 0) {
+ fprintf(stderr,
+ "%s - Failed to parse command line parameters\n",
+ strerror(errno));
+ return -1;
+ }
+
+ lxc_rexec_as_memfd(argv, envp, memfd_name);
+ fprintf(stderr, "%s - Failed to rexec as memfd\n", strerror(errno));
+ return -1;
+}
+
+/**
+ * This function will copy any binary that calls liblxc into a memory file and
+ * will use the memfd to rexecute the binary. This is done to prevent attacks
+ * through the /proc/self/exe symlink to corrupt the host binary when host and
+ * container are in the same user namespace or have set up an identity id
+ * mapping: CVE-2019-5736.
+ */
+__attribute__((constructor)) static void liblxc_rexec(void)
+{
+ if (lxc_rexec("liblxc")) {
+ fprintf(stderr, "Failed to re-execute liblxc via memory file descriptor\n");
+ _exit(EXIT_FAILURE);
+ }
+}
projects / thirdparty / lxc.git / commitdiff
