Do not print backtraces on fatal glibc errors

If the process is in a bad state, we used to print backtraces in
many cases.  This is problematic because doing so could involve
a lot of work, like loading libgcc_s using the dynamic linker,
and this could itself be targeted by exploit writers.  For example,
if the crashing process was forked from a long-lived process, the
addresses in the error message could be used to bypass ASLR.

Commit ed421fca42fd9b4cab7c66e77894b8dd7ca57ed0 ("Avoid backtrace from
__stack_chk_fail [BZ #12189]"), backtraces where no longer printed
because backtrace_and_maps was always called with do_abort == 1.

Rather than fixing this logic error, this change removes the backtrace
functionality from the sources.  With the prevalence of external crash
handlers, it does not appear to be particularly useful.  The crash
handler may also destroy useful information for debugging.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

2 files changed, 4 insertions, 64 deletions

diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
index 3906af5ee7..9ddbfa7314 100644
--- a/sysdeps/posix/libc_fatal.c
+++ b/sysdeps/posix/libc_fatal.c
@@ -45,16 +45,6 @@ writev_for_fatal (int fd, const struct iovec *iov, size_t niov, size_t total)
 }
 #endif
 
-#ifndef BEFORE_ABORT
-# define BEFORE_ABORT		before_abort
-static void
-before_abort (int do_abort __attribute__ ((unused)),
-              bool written __attribute__ ((unused)),
-              int fd __attribute__ ((unused)))
-{
-}
-#endif
-
 struct str_list
 {
   const char *str;
@@ -75,17 +65,6 @@ __libc_message (enum __libc_message_action action, const char *fmt, ...)
   FATAL_PREPARE;
 #endif
 
-  /* Don't call __libc_secure_getenv if we aren't doing backtrace, which
-     may access the corrupted stack.  */
-  if ((action & do_backtrace))
-    {
-      /* Open a descriptor for /dev/tty unless the user explicitly
-	 requests errors on standard error.  */
-      const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
-      if (on_2 == NULL || *on_2 == '\0')
-	fd = __open_nocancel (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);
-    }
-
   if (fd == -1)
     fd = STDERR_FILENO;
 
@@ -129,7 +108,6 @@ __libc_message (enum __libc_message_action action, const char *fmt, ...)
       ++nlist;
     }
 
-  bool written = false;
   if (nlist > 0)
     {
       struct iovec *iov = alloca (nlist * sizeof (struct iovec));
@@ -143,7 +121,7 @@ __libc_message (enum __libc_message_action action, const char *fmt, ...)
 	  list = list->next;
 	}
 
-      written = WRITEV_FOR_FATAL (fd, iov, nlist, total);
+      WRITEV_FOR_FATAL (fd, iov, nlist, total);
 
       if ((action & do_abort))
 	{
@@ -173,13 +151,8 @@ __libc_message (enum __libc_message_action action, const char *fmt, ...)
   va_end (ap);
 
   if ((action & do_abort))
-    {
-      if ((action & do_backtrace))
-	BEFORE_ABORT (do_abort, written, fd);
-
-      /* Kill the application.  */
-      abort ();
-    }
+    /* Kill the application.  */
+    abort ();
 }
 
 
@@ -188,6 +161,6 @@ __libc_fatal (const char *message)
 {
   /* The loop is added only to keep gcc happy.  */
   while (1)
-    __libc_message (do_abort | do_backtrace, "%s", message);
+    __libc_message (do_abort, "%s", message);
 }
 libc_hidden_def (__libc_fatal)
diff --git a/sysdeps/unix/sysv/linux/libc_fatal.c b/sysdeps/unix/sysv/linux/libc_fatal.c
index 56c626339f..50a613e31f 100644
--- a/sysdeps/unix/sysv/linux/libc_fatal.c
+++ b/sysdeps/unix/sysv/linux/libc_fatal.c
@@ -17,11 +17,6 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <errno.h>
-#include <execinfo.h>
-#include <fcntl.h>
-#include <not-cancel.h>
-#include <string.h>
-#include <sys/mman.h>
 #include <sys/uio.h>
 
 static bool
@@ -37,32 +32,4 @@ writev_for_fatal (int fd, const struct iovec *iov, size_t niov, size_t total)
 }
 #define WRITEV_FOR_FATAL	writev_for_fatal
 
-static void
-backtrace_and_maps (int do_abort, bool written, int fd)
-{
-  if (do_abort > 1 && written)
-    {
-      void *addrs[64];
-#define naddrs (sizeof (addrs) / sizeof (addrs[0]))
-      int n = __backtrace (addrs, naddrs);
-      if (n > 2)
-        {
-#define strnsize(str) str, strlen (str)
-#define writestr(str) __write_nocancel (fd, str)
-          writestr (strnsize ("======= Backtrace: =========\n"));
-          __backtrace_symbols_fd (addrs + 1, n - 1, fd);
-
-          writestr (strnsize ("======= Memory map: ========\n"));
-          int fd2 = __open_nocancel ("/proc/self/maps", O_RDONLY);
-          char buf[1024];
-          ssize_t n2;
-          while ((n2 = __read_nocancel (fd2, buf, sizeof (buf))) > 0)
-            if (__write_nocancel (fd, buf, n2) != n2)
-              break;
-          __close_nocancel_nostatus (fd2);
-        }
-    }
-}
-#define BEFORE_ABORT		backtrace_and_maps
-
 #include <sysdeps/posix/libc_fatal.c>