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/* Copyright (c) 2013, The Tor Project, Inc. */
/* See LICENSE for licensing information */
#define __USE_GNU
#define _GNU_SOURCE 1
#include "orconfig.h"
#include "compat.h"
#include "util.h"
#include "torlog.h"
#ifdef HAVE_EXECINFO_H
#include <execinfo.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SIGNAL_H
#include <signal.h>
#endif
#ifdef HAVE_CYGWIN_SIGNAL_H
#include <cygwin/signal.h>
#elif defined(HAVE_SYS_UCONTEXT_H)
#include <sys/ucontext.h>
#elif defined(HAVE_UCONTEXT_H)
#include <ucontext.h>
#endif
#define EXPOSE_CLEAN_BACKTRACE
#include "backtrace.h"
#if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE) && \
defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION)
#define USE_BACKTRACE
#endif
#if !defined(USE_BACKTRACE)
#define NO_BACKTRACE_IMPL
#endif
/** Version of Tor to report in backtrace messages. */
static char *bt_version = NULL;
#ifdef USE_BACKTRACE
/** Largest stack depth to try to dump. */
#define MAX_DEPTH 256
/** Static allocation of stack to dump. This is static so we avoid stack
* pressure. */
static void *cb_buf[MAX_DEPTH];
/** Protects cb_buf from concurrent access */
static tor_mutex_t cb_buf_mutex;
/** Change a stacktrace in <b>stack</b> of depth <b>depth</b> so that it will
* log the correct function from which a signal was received with context
* <b>ctx</b>. (When we get a signal, the current function will not have
* called any other function, and will therefore have not pushed its address
* onto the stack. Fortunately, we usually have the program counter in the
* ucontext_t structure.
*/
void
clean_backtrace(void **stack, int depth, const ucontext_t *ctx)
{
#ifdef PC_FROM_UCONTEXT
#if defined(__linux__)
const int n = 1;
#elif defined(__darwin__) || defined(__APPLE__) || defined(__OpenBSD__) \
|| defined(__FreeBSD__)
const int n = 2;
#else
const int n = 1;
#endif
if (depth <= n)
return;
stack[n] = (void*) ctx->PC_FROM_UCONTEXT;
#else
(void) depth;
(void) ctx;
#endif
}
/** Log a message <b>msg</b> at <b>severity</b> in <b>domain</b>, and follow
* that with a backtrace log. */
void
log_backtrace(int severity, int domain, const char *msg)
{
int depth;
char **symbols;
int i;
tor_mutex_acquire(&cb_buf_mutex);
depth = backtrace(cb_buf, MAX_DEPTH);
symbols = backtrace_symbols(cb_buf, depth);
tor_log(severity, domain, "%s. Stack trace:", msg);
if (!symbols) {
tor_log(severity, domain, " Unable to generate backtrace.");
goto done;
}
for (i=0; i < depth; ++i) {
tor_log(severity, domain, " %s", symbols[i]);
}
free(symbols);
done:
tor_mutex_release(&cb_buf_mutex);
}
static void crash_handler(int sig, siginfo_t *si, void *ctx_)
__attribute__((noreturn));
/** Signal handler: write a crash message with a stack trace, and die. */
static void
crash_handler(int sig, siginfo_t *si, void *ctx_)
{
char buf[40];
int depth;
ucontext_t *ctx = (ucontext_t *) ctx_;
int n_fds, i;
const int *fds = NULL;
(void) si;
depth = backtrace(cb_buf, MAX_DEPTH);
/* Clean up the top stack frame so we get the real function
* name for the most recently failing function. */
clean_backtrace(cb_buf, depth, ctx);
format_dec_number_sigsafe((unsigned)sig, buf, sizeof(buf));
tor_log_err_sigsafe(bt_version, " died: Caught signal ", buf, "\n",
NULL);
n_fds = tor_log_get_sigsafe_err_fds(&fds);
for (i=0; i < n_fds; ++i)
backtrace_symbols_fd(cb_buf, depth, fds[i]);
abort();
}
/** Install signal handlers as needed so that when we crash, we produce a
* useful stack trace. Return 0 on success, -1 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;
tor_mutex_init(&cb_buf_mutex);
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = crash_handler;
sa.sa_flags = SA_SIGINFO;
sigfillset(&sa.sa_mask);
for (i = 0; trap_signals[i] >= 0; ++i) {
if (sigaction(trap_signals[i], &sa, NULL) == -1) {
log_warn(LD_BUG, "Sigaction failed: %s", strerror(errno));
rv = -1;
}
}
{
/* Now, generate (but do not log) a backtrace. This ensures that
* libc has pre-loaded the symbols we need to dump things, so that later
* reads won't be denied by the sandbox code */
char **symbols;
int depth = backtrace(cb_buf, MAX_DEPTH);
symbols = backtrace_symbols(cb_buf, depth);
if (symbols)
free(symbols);
}
return rv;
}
/** Uninstall crash handlers. */
static void
remove_bt_handler(void)
{
tor_mutex_uninit(&cb_buf_mutex);
}
#endif
#ifdef NO_BACKTRACE_IMPL
void
log_backtrace(int severity, int domain, const char *msg)
{
tor_log(severity, domain, "%s. (Stack trace not available)", msg);
}
static int
install_bt_handler(void)
{
return 0;
}
static void
remove_bt_handler(void)
{
}
#endif
/** Set up code to handle generating error messages on crashes. */
int
configure_backtrace_handler(const char *tor_version)
{
tor_free(bt_version);
if (!tor_version)
tor_version = "";
tor_asprintf(&bt_version, "Tor %s", tor_version);
return install_bt_handler();
}
/** Perform end-of-process cleanup for code that generates error messages on
* crashes. */
void
clean_up_backtrace_handler(void)
{
remove_bt_handler();
tor_free(bt_version);
}
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