Merge branch 'tor-github/pr/1302'

changes/bug31614

@@ -0,0 +1,9 @@
+  o Minor bugfixes (logging):
+    - Disable backtrace signal handlers when shutting down tor.
+      Fixes bug 31614; bugfix on 0.2.5.2-alpha.
+    - Add a missing check for HAVE_PTHREAD_H, because the backtrace code uses
+      mutexes. Fixes bug 31614; bugfix on 0.2.5.2-alpha.
+  o Documentation:
+    - Explain why we can't destroy the backtrace buffer mutex. Explain why
+      we don't need to destroy the log mutex.
+      Closes ticket 31736.

src/lib/err/backtrace.c

@@ -57,7 +57,8 @@
 #include "lib/err/torerr.h"
 
 #if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE) && \
-  defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION)
+  defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION) && \
+  defined(HAVE_PTHREAD_H)
 #define USE_BACKTRACE
 #endif
 
@@ -190,13 +191,15 @@ dump_stack_symbols_to_error_fds(void)
     backtrace_symbols_fd(cb_buf, (int)depth, fds[i]);
 }
 
+/* The signals that we want our backtrace handler to trap */
+static int trap_signals[] = { SIGSEGV, SIGILL, SIGFPE, SIGBUS, SIGSYS,
+  SIGIO, -1 };
+
 /** Install signal handlers as needed so that when we crash, we produce a
  * useful stack trace. Return 0 on success, -errno on failure. */
 static int
 install_bt_handler(void)
 {
-  int trap_signals[] = { SIGSEGV, SIGILL, SIGFPE, SIGBUS, SIGSYS,
-                         SIGIO, -1 };
   int i, rv=0;
 
   struct sigaction sa;
@@ -232,6 +235,23 @@ install_bt_handler(void)
 static void
 remove_bt_handler(void)
 {
+  int i;
+
+  struct sigaction sa;
+
+  memset(&sa, 0, sizeof(sa));
+  sa.sa_handler = SIG_DFL;
+  sigfillset(&sa.sa_mask);
+
+  for (i = 0; trap_signals[i] >= 0; ++i) {
+    /* remove_bt_handler() is called on shutdown, from low-level code.
+     * It's not a fatal error, so we just ignore it. */
+    (void)sigaction(trap_signals[i], &sa, NULL);
+  }
+
+  /* cb_buf_mutex is statically initialised, so we can not destroy it.
+   * If we destroy it, and then re-initialise tor, all our backtraces will
+   * fail. */
 }
 #endif /* defined(USE_BACKTRACE) */
 

src/lib/log/log.c

@@ -832,7 +832,10 @@ logs_free_all(void)
   }
 
   /* We _could_ destroy the log mutex here, but that would screw up any logs
-   * that happened between here and the end of execution. */
+   * that happened between here and the end of execution.
+   * If tor is re-initialized, log_mutex_initialized will still be 1. So we
+   * won't trigger any undefined behaviour by trying to re-initialize the
+   * log mutex. */
 }
 
 /** Close signal-safe log files.

src/lib/sandbox/sandbox.c

@@ -294,6 +294,7 @@ sb_rt_sigaction(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
   unsigned i;
   int rc;
   int param[] = { SIGINT, SIGTERM, SIGPIPE, SIGUSR1, SIGUSR2, SIGHUP, SIGCHLD,
+                  SIGSEGV, SIGILL, SIGFPE, SIGBUS, SIGSYS, SIGIO,
 #ifdef SIGXFSZ
       SIGXFSZ
 #endif