Implement DisableAllSwap to avoid putting secret info in page files.

This commit implements a new config option: 'DisableAllSwap'
This option probably only works properly when Tor is started as root.
We added two new functions: tor_mlockall() and tor_set_max_memlock().
tor_mlockall() attempts to mlock() all current and all future memory pages.
For tor_mlockall() to work properly we set the process rlimits for memory to
RLIM_INFINITY (and beyond) inside of tor_set_max_memlock().
We behave differently from mlockall() by only allowing tor_mlockall() to be
called one single time. All other calls will result in a return code of 1.
It is not possible to change DisableAllSwap while running.
A sample configuration item was added to the torrc.complete.in config file.
A new item in the man page for DisableAllSwap was added.
Thanks to Moxie Marlinspike and Chris Palmer for their feedback on this patch.

Please note that we make no guarantees about the quality of your OS and its
mlock/mlockall implementation. It is possible that this will do nothing at all.
It is also possible that you can ulimit the mlock properties of a given user
such that root is not required. This has not been extensively tested and is
unsupported. I have included some comments for possible ways we can handle
this on win32.

2 files changed, 101 insertions, 0 deletions

diff --git a/src/common/compat.c b/src/common/compat.c
index e1a275de11..9e5dca3525 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -2204,6 +2204,105 @@ tor_threads_init(void)
 }
 #endif
 
+#ifdef HAVE_SYS_MMAN_H
+/** Attempt to raise the current and max rlimit to infinity for our process.
+ * This only needs to be done once and can probably only be done when we have
+ * not already dropped privileges.
+ */
+static int
+tor_set_max_memlock(void)
+{
+  /* Future consideration for Windows is probably SetProcessWorkingSetSize
+   * This is similar to setting the memory rlimit of RLIMIT_MEMLOCK
+   * http://msdn.microsoft.com/en-us/library/ms686234(VS.85).aspx
+   */
+
+  struct rlimit limit;
+  int ret;
+
+  /* Do we want to report current limits first? This is not really needed. */
+  ret = getrlimit(RLIMIT_MEMLOCK, &limit);
+  if (ret == -1) {
+    log_warn(LD_GENERAL, "Could not get RLIMIT_MEMLOCK: %s", strerror(errno));
+    return -1;
+  }
+
+  /* RLIM_INFINITY is -1 on some platforms. */
+  limit.rlim_cur = RLIM_INFINITY;
+  limit.rlim_max = RLIM_INFINITY;
+
+  ret = setrlimit(RLIMIT_MEMLOCK, &limit);
+  if (ret == -1) {
+    if (errno == EPERM) {
+      log_warn(LD_GENERAL, "You appear to lack permissions to change memory "
+                           "limits. Are you root?");
+      log_warn(LD_GENERAL, "Unable to raise RLIMIT_MEMLOCK: %s",
+               strerror(errno));
+    } else {
+      log_warn(LD_GENERAL, "Could not raise RLIMIT_MEMLOCK: %s",
+               strerror(errno));
+    }
+    return -1;
+  }
+
+  return 0;
+}
+#endif
+
+/** Attempt to lock all current and all future memory pages.
+ * This should only be called once and while we're privileged.
+ * Like mlockall() we return 0 when we're successful and -1 when we're not.
+ * Unlike mlockall() we return 1 if we've already attempted to lock memory.
+ */
+int
+tor_mlockall(void)
+{
+  static int memory_lock_attempted = 0;
+  int ret;
+
+  if (memory_lock_attempted) {
+    return 1;
+  }
+
+  memory_lock_attempted = 1;
+
+  /*
+   * Future consideration for Windows may be VirtualLock
+   * VirtualLock appears to implement mlock() but not mlockall()
+   *
+   * http://msdn.microsoft.com/en-us/library/aa366895(VS.85).aspx
+   */
+
+#ifdef HAVE_SYS_MMAN_H
+  ret = tor_set_max_memlock();
+  if (ret == 0) {
+    /* Perhaps we only want to log this if we're in a verbose mode? */
+    log_notice(LD_GENERAL, "RLIMIT_MEMLOCK is now set to RLIM_INFINITY.");
+  }
+
+  ret = mlockall(MCL_CURRENT|MCL_FUTURE);
+  if (ret == 0) {
+    log_notice(LD_GENERAL, "Insecure OS paging is effectively disabled.");
+    return 0;
+  } else {
+    if (errno == ENOSYS) {
+      /* Apple - it's 2009! I'm looking at you. Grrr. */
+      log_notice(LD_GENERAL, "It appears that mlockall() is not available on "
+                             "your platform.");
+    } else if (errno == EPERM) {
+      log_notice(LD_GENERAL, "It appears that you lack the permissions to "
+                             "lock memory. Are you root?");
+    }
+    log_notice(LD_GENERAL, "Unable to lock all current and future memory "
+                           "pages: %s", strerror(errno));
+    return -1;
+  }
+#else
+  log_warn(LD_GENERAL, "Unable to lock memory pages. mlockall() unsupported?");
+  return -1;
+#endif
+}
+
 /** Identity of the "main" thread */
 static unsigned long main_thread_id = -1;
 
diff --git a/src/common/compat.h b/src/common/compat.h
index edd09d8683..554ae8919f 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -509,6 +509,8 @@ typedef struct tor_mutex_t {
 #endif
 } tor_mutex_t;
 
+int tor_mlockall(void);
+
 #ifdef TOR_IS_MULTITHREADED
 tor_mutex_t *tor_mutex_new(void);
 void tor_mutex_init(tor_mutex_t *m);