commit cc9e86db61e2ffb6c54b09e8c41e8fdad50b3ef3 Author: Nick Mathewson nickm@torproject.org Date: Thu Apr 10 15:44:52 2014 -0400
Log a backtrace when the sandbox finds a failure
This involves some duplicate code between backtrace.c and sandbox.c, but I don't see a way around it: calling more functions would mean adding more steps to our call stack, and running clean_backtrace() against the wrong point on the stack. --- src/common/backtrace.c | 18 ++++++++++++++++-- src/common/backtrace.h | 6 ++++++ src/common/sandbox.c | 35 +++++++++++++++++++++++++++++++++++ 3 files changed, 57 insertions(+), 2 deletions(-)
diff --git a/src/common/backtrace.c b/src/common/backtrace.c index 239c657..3a073a8 100644 --- a/src/common/backtrace.c +++ b/src/common/backtrace.c @@ -5,7 +5,6 @@ #define _GNU_SOURCE 1
#include "orconfig.h" -#include "backtrace.h" #include "compat.h" #include "util.h" #include "torlog.h" @@ -31,6 +30,9 @@ #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 @@ -59,7 +61,7 @@ static tor_mutex_t cb_buf_mutex; * onto the stack. Fortunately, we usually have the program counter in the * ucontext_t structure. */ -static void +void clean_backtrace(void **stack, int depth, const ucontext_t *ctx) { #ifdef PC_FROM_UCONTEXT @@ -165,6 +167,18 @@ install_bt_handler(void) 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; }
diff --git a/src/common/backtrace.h b/src/common/backtrace.h index 765436f..b1df281 100644 --- a/src/common/backtrace.h +++ b/src/common/backtrace.h @@ -4,9 +4,15 @@ #ifndef TOR_BACKTRACE_H #define TOR_BACKTRACE_H
+#include "orconfig.h" + void log_backtrace(int severity, int domain, const char *msg); int configure_backtrace_handler(const char *tor_version); void clean_up_backtrace_handler(void);
+#ifdef EXPOSE_CLEAN_BACKTRACE +void clean_backtrace(void **stack, int depth, const ucontext_t *ctx); +#endif + #endif
diff --git a/src/common/sandbox.c b/src/common/sandbox.c index 0a7a129..0548f3e 100644 --- a/src/common/sandbox.c +++ b/src/common/sandbox.c @@ -56,6 +56,17 @@ #include <time.h> #include <poll.h>
+#if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE) && \ + defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION) +#define USE_BACKTRACE +#define EXPOSE_CLEAN_BACKTRACE +#include "backtrace.h" +#endif + +#ifdef USE_BACKTRACE +#include <execinfo.h> +#endif + /**Determines if at least one sandbox is active.*/ static int sandbox_active = 0; /** Holds the parameter list configuration for the sandbox.*/ @@ -1308,6 +1319,11 @@ install_syscall_filter(sandbox_cfg_t* cfg) return (rc < 0 ? -rc : rc); }
+#ifdef USE_BACKTRACE +#define MAX_DEPTH 256 +static void *syscall_cb_buf[MAX_DEPTH]; +#endif + /** * Function called when a SIGSYS is caught by the application. It notifies the * user that an error has occurred and either terminates or allows the @@ -1319,6 +1335,12 @@ sigsys_debugging(int nr, siginfo_t *info, void *void_context) ucontext_t *ctx = (ucontext_t *) (void_context); char number[32]; int syscall; +#ifdef USE_BACKTRACE + int depth; + int n_fds, i; + const int *fds = NULL; +#endif + (void) nr;
if (info->si_code != SYS_SECCOMP) @@ -1329,12 +1351,25 @@ sigsys_debugging(int nr, siginfo_t *info, void *void_context)
syscall = (int) ctx->uc_mcontext.gregs[REG_SYSCALL];
+#ifdef USE_BACKTRACE + depth = backtrace(syscall_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(syscall_cb_buf, depth, ctx); +#endif + format_dec_number_sigsafe(syscall, number, sizeof(number)); tor_log_err_sigsafe("(Sandbox) Caught a bad syscall attempt (syscall ", number, ")\n", NULL);
+#ifdef USE_BACKTRACE + n_fds = tor_log_get_sigsafe_err_fds(&fds); + for (i=0; i < n_fds; ++i) + backtrace_symbols_fd(syscall_cb_buf, depth, fds[i]); +#endif + #if defined(DEBUGGING_CLOSE) _exit(1); #endif // DEBUGGING_CLOSE