log: Close log and err file descriptors before aborting

Part of 31594.

src/lib/err/backtrace.c

@@ -172,7 +172,7 @@ crash_handler(int sig, siginfo_t *si, void *ctx_)
   for (i=0; i < n_fds; ++i)
     backtrace_symbols_fd(cb_buf, (int)depth, fds[i]);
 
-  abort();
+  tor_raw_abort_();
 }
 
 /** Write a backtrace to all of the emergency-error fds. */

src/lib/err/torerr.c

@@ -208,6 +208,18 @@ tor_raw_assertion_failed_msg_(const char *file, int line, const char *expr,
   dump_stack_symbols_to_error_fds();
 }
 
+/**
+ * Call the abort() function to kill the current process with a fatal
+ * error. But first, close the raw error file descriptors, so error messages
+ * are written before process termination.
+ **/
+void
+tor_raw_abort_(void)
+{
+  tor_log_close_sigsafe_err_fds();
+  abort();
+}
+
 /* As format_{hex,dex}_number_sigsafe, but takes a <b>radix</b> argument
  * in range 2..16 inclusive. */
 static int
@@ -242,7 +254,7 @@ format_number_sigsafe(unsigned long x, char *buf, int buf_len,
     unsigned digit = (unsigned) (x % radix);
     if (cp <= buf) {
       /* Not tor_assert(); see above. */
-      abort();
+      tor_raw_abort_();
     }
     --cp;
     *cp = "0123456789ABCDEF"[digit];
@@ -251,7 +263,7 @@ format_number_sigsafe(unsigned long x, char *buf, int buf_len,
 
   /* NOT tor_assert; see above. */
   if (cp != buf) {
-    abort(); // LCOV_EXCL_LINE
+    tor_raw_abort_(); // LCOV_EXCL_LINE
   }
 
   return len;

src/lib/err/torerr.h

@@ -20,13 +20,13 @@
 #define raw_assert(expr) STMT_BEGIN                                     \
     if (!(expr)) {                                                      \
       tor_raw_assertion_failed_msg_(__FILE__, __LINE__, #expr, NULL);   \
-      abort();                                                          \
+      tor_raw_abort_();                                                 \
     }                                                                   \
   STMT_END
 #define raw_assert_unreached(expr) raw_assert(0)
 #define raw_assert_unreached_msg(msg) STMT_BEGIN                    \
     tor_raw_assertion_failed_msg_(__FILE__, __LINE__, "0", (msg));  \
-    abort();                                                        \
+    tor_raw_abort_();                                               \
   STMT_END
 
 void tor_raw_assertion_failed_msg_(const char *file, int line,
@@ -43,6 +43,8 @@ void tor_log_reset_sigsafe_err_fds(void);
 void tor_log_close_sigsafe_err_fds(void);
 void tor_log_sigsafe_err_set_granularity(int ms);
 
+void tor_raw_abort_(void) ATTR_NORETURN;
+
 int format_hex_number_sigsafe(unsigned long x, char *buf, int max_len);
 int format_dec_number_sigsafe(unsigned long x, char *buf, int max_len);
 

src/lib/log/log.c

@@ -224,6 +224,7 @@ int log_global_min_severity_ = LOG_NOTICE;
 
 static void delete_log(logfile_t *victim);
 static void close_log(logfile_t *victim);
+static void close_log_sigsafe(logfile_t *victim);
 
 static char *domain_to_string(log_domain_mask_t domain,
                              char *buf, size_t buflen);
@@ -833,6 +834,30 @@ logs_free_all(void)
    * that happened between here and the end of execution. */
 }
 
+/** Close signal-safe log files.
+ * Closing the log files makes the process and OS flush log buffers.
+ *
+ * This function is safe to call from a signal handler. It should only be
+ * called when shutting down the log or err modules. It is currenly called
+ * by the err module, when terminating the process on an abnormal condition.
+ */
+void
+logs_close_sigsafe(void)
+{
+  logfile_t *victim, *next;
+  /* We can't LOCK_LOGS() in a signal handler, because it may call
+   * signal-unsafe functions. And we can't deallocate memory, either. */
+  next = logfiles;
+  logfiles = NULL;
+  while (next) {
+    victim = next;
+    next = next->next;
+    if (victim->needs_close) {
+      close_log_sigsafe(victim);
+    }
+  }
+}
+
 /** Remove and free the log entry <b>victim</b> from the linked-list
  * logfiles (it is probably present, but it might not be due to thread
  * racing issues). After this function is called, the caller shouldn't
@@ -858,14 +883,27 @@ delete_log(logfile_t *victim)
   log_free(victim);
 }
 
+/** Helper: release system resources (but not memory) held by a single
+ * signal-safe logfile_t. If the log's resources can not be released in
+ * a signal handler, does nothing. */
+static void
+close_log_sigsafe(logfile_t *victim)
+{
+  if (victim->needs_close && victim->fd >= 0) {
+    /* We can't do anything useful here if close() fails: we're shutting
+     * down logging, and the err module only does fatal errors. */
+    close(victim->fd);
+    victim->fd = -1;
+  }
+}
+
 /** Helper: release system resources (but not memory) held by a single
  * logfile_t. */
 static void
 close_log(logfile_t *victim)
 {
-  if (victim->needs_close && victim->fd >= 0) {
-    close(victim->fd);
-    victim->fd = -1;
+  if (victim->needs_close) {
+    close_log_sigsafe(victim);
   } else if (victim->is_syslog) {
 #ifdef HAVE_SYSLOG_H
     if (--syslog_count == 0) {

src/lib/log/log.h

@@ -170,6 +170,7 @@ void logs_set_domain_logging(int enabled);
 int get_min_log_level(void);
 void switch_logs_debug(void);
 void logs_free_all(void);
+void logs_close_sigsafe(void);
 void add_temp_log(int min_severity);
 void close_temp_logs(void);
 void rollback_log_changes(void);

src/lib/log/util_bug.c

@@ -11,6 +11,7 @@
 #include "lib/log/util_bug.h"
 #include "lib/log/log.h"
 #include "lib/err/backtrace.h"
+#include "lib/err/torerr.h"
 #ifdef TOR_UNIT_TESTS
 #include "lib/smartlist_core/smartlist_core.h"
 #include "lib/smartlist_core/smartlist_foreach.h"
@@ -122,16 +123,18 @@ tor_bug_occurred_(const char *fname, unsigned int line,
 }
 
 /**
- * Call the abort() function to kill the current process with a fatal
- * error.
+ * Call the tor_raw_abort_() function to close raw logs, then kill the current
+ * process with a fatal error. But first, close the file-based log file
+ * descriptors, so error messages are written before process termination.
  *
  * (This is a separate function so that we declare it in util_bug.h without
- * including stdlib in all the users of util_bug.h)
+ * including torerr.h in all the users of util_bug.h)
  **/
 void
 tor_abort_(void)
 {
-  abort();
+  logs_close_sigsafe();
+  tor_raw_abort_();
 }
 
 #ifdef _WIN32

src/trunnel/trunnel-local.h

@@ -14,5 +14,6 @@
 #define trunnel_reallocarray tor_reallocarray
 #define trunnel_assert tor_assert
 #define trunnel_memwipe(mem, len) memwipe((mem), 0, (len))
+#define trunnel_abort tor_abort_
 
 #endif