conf: copy mountinfo for remount_all_slave()

While a container reads mountinfo from proc fs, the mountinfo can be changed by
the kernel anytime. This has caused critical issues on some devices.

Signed-off-by: Donghwa Jeong dh48.jeong@samsung.com
Reported-by: Donghwa Jeong dh48.jeong@samsung.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 06667584a84bd36356cdb97f158740a1ae6910db..7714eccf528d7e08f35bed92731d5e5fc0b507df 100644 (file)
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -24,34 +24,35 @@
 #define _GNU_SOURCE
 #include "config.h"
 
+#include <arpa/inet.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <grp.h>
 #include <inttypes.h>
 #include <libgen.h>
+#include <linux/loop.h>
+#include <net/if.h>
+#include <netinet/in.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <time.h>
-#include <unistd.h>
-#include <arpa/inet.h>
-#include <linux/loop.h>
-#include <net/if.h>
-#include <netinet/in.h>
 #include <sys/mman.h>
 #include <sys/mount.h>
 #include <sys/param.h>
 #include <sys/prctl.h>
-#include <sys/stat.h>
+#include <sys/sendfile.h>
 #include <sys/socket.h>
-#include <sys/sysmacros.h>
+#include <sys/stat.h>
 #include <sys/syscall.h>
+#include <sys/sysmacros.h>
 #include <sys/types.h>
 #include <sys/utsname.h>
 #include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
 
 /* makedev() */
 #ifdef MAJOR_IN_MKDEV
@@ -3013,38 +3014,117 @@ void tmp_proc_unmount(struct lxc_conf *lxc_conf)
        }
 }
 
+#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;
+}
+
+/* Walk /proc/mounts and change any shared entries to slave. */
 void remount_all_slave(void)
 {
-       /* walk /proc/mounts and change any shared entries to slave */
-       FILE *f = fopen("/proc/self/mountinfo", "r");
-       char *line = NULL;
+       int memfd, mntinfo_fd, ret;
+       ssize_t copied;
+       FILE *f;
        size_t len = 0;
+       char *line = NULL;
+
+       mntinfo_fd = open("/proc/self/mountinfo", O_RDONLY | O_CLOEXEC);
+       if (mntinfo_fd < 0) {
+               SYSERROR("Failed to open \"/proc/self/mountinfo\"");
+               return;
+       }
+
+       memfd = memfd_create(".lxc_mountinfo", MFD_CLOEXEC);
+       if (memfd < 0) {
+               char template[] = P_tmpdir "/.lxc_mountinfo_XXXXXX";
+
+               if (errno != ENOSYS) {
+                       SYSERROR("Failed to create temporary in-memory file");
+                       close(mntinfo_fd);
+                       return;
+               }
+
+               memfd = lxc_make_tmpfile(template, true);
+               if (memfd < 0) {
+                       close(mntinfo_fd);
+                       WARN("Failed to create temporary file");
+                       return;
+               }
+       }
+
+again:
+       copied = lxc_sendfile_nointr(memfd, mntinfo_fd, NULL, LXC_SENDFILE_MAX);
+       if (copied < 0) {
+               if (errno == EINTR)
+                       goto again;
 
+               SYSERROR("Failed to copy \"/proc/self/mountinfo\"");
+               close(mntinfo_fd);
+               close(memfd);
+               return;
+       }
+       close(mntinfo_fd);
+
+       /* After a successful fdopen() memfd will be closed when calling
+        * fclose(f). Calling close(memfd) afterwards is undefined.
+        */
+       ret = lseek(memfd, 0, SEEK_SET);
+       if (ret < 0) {
+               SYSERROR("Failed to reset file descriptor offset");
+               close(memfd);
+               return;
+       }
+
+       f = fdopen(memfd, "r");
        if (!f) {
-               SYSERROR("Failed to open /proc/self/mountinfo to mark all shared");
-               ERROR("Continuing container startup...");
+               SYSERROR("Failed to open copy of \"/proc/self/mountinfo\" to mark "
+                               "all shared. Continuing");
+               close(memfd);
                return;
        }
 
        while (getline(&line, &len, f) != -1) {
-               char *target, *opts;
+               int ret;
+               char *opts, *target;
+
                target = get_field(line, 4);
                if (!target)
                        continue;
+
                opts = get_field(target, 2);
                if (!opts)
                        continue;
+
                null_endofword(opts);
                if (!strstr(opts, "shared"))
                        continue;
+
                null_endofword(target);
-               if (mount(NULL, target, NULL, MS_SLAVE, NULL)) {
-                       SYSERROR("Failed to make %s rslave", target);
+               ret = mount(NULL, target, NULL, MS_SLAVE, NULL);
+               if (ret < 0) {
+                       SYSERROR("Failed to make \"%s\" MS_SLAVE", target);
                        ERROR("Continuing...");
+                       continue;
                }
+               TRACE("Remounted \"%s\" as MS_SLAVE", target);
        }
        fclose(f);
        free(line);
+       TRACE("Remounted all mount table entries as MS_SLAVE");
 }
 
 void lxc_execute_bind_init(struct lxc_conf *conf)