stdlib: Make abort/_Exit AS-safe (BZ 26275)

The recursive lock used on abort does not synchronize with a new process
creation (either by fork-like interfaces or posix_spawn ones), nor it
is reinitialized after fork().

Also, the SIGABRT unblock before raise() shows another race condition,
where a fork or posix_spawn() call by another thread, just after the
recursive lock release and before the SIGABRT signal, might create
programs with a non-expected signal mask.  With the default option
(without POSIX_SPAWN_SETSIGDEF), the process can see SIG_DFL for
SIGABRT, where it should be SIG_IGN.

To fix the AS-safe, raise() does not change the process signal mask,
and an AS-safe lock is used if a SIGABRT is installed or the process
is blocked or ignored.  With the signal mask change removal,
there is no need to use a recursive loc.  The lock is also taken on
both _Fork() and posix_spawn(), to avoid the spawn process to see the
abort handler as SIG_DFL.

A read-write lock is used to avoid serialize _Fork and posix_spawn
execution.  Both sigaction (SIGABRT) and abort() requires to lock
as writer (since both change the disposition).

The fallback is also simplified: there is no need to use a loop of
ABORT_INSTRUCTION after _exit() (if the syscall does not terminate the
process, the system is broken).

The proposed fix changes how setjmp works on a SIGABRT handler, where
glibc does not save the signal mask.  So usage like the below will now
always abort.

  static volatile int chk_fail_ok;
  static jmp_buf chk_fail_buf;

  static void
  handler (int sig)
  {
    if (chk_fail_ok)
      {
        chk_fail_ok = 0;
        longjmp (chk_fail_buf, 1);
      }
    else
      _exit (127);
  }
  [...]
  signal (SIGABRT, handler);
  [....]
  chk_fail_ok = 1;
  if (! setjmp (chk_fail_buf))
    {
      // Something that can calls abort, like a failed fortify function.
      chk_fail_ok = 0;
      printf ("FAIL\n");
    }

Such cases will need to use sigsetjmp instead.

The _dl_start_profile calls sigaction through _profil, and to avoid
pulling abort() on loader the call is replaced with __libc_sigaction.

Checked on x86_64-linux-gnu and aarch64-linux-gnu.

Reviewed-by: DJ Delorie <dj@redhat.com>

2 files changed, 51 insertions, 2 deletions

diff --git a/sysdeps/generic/internal-signals.h b/sysdeps/generic/internal-signals.h
index 3db100b..e031a96 100644
--- a/sysdeps/generic/internal-signals.h
+++ b/sysdeps/generic/internal-signals.h
@@ -20,6 +20,7 @@
 # define __INTERNAL_SIGNALS_H
 
 #include <signal.h>
+#include <internal-sigset.h>
 #include <sigsetops.h>
 #include <stdbool.h>
 #include <stddef.h>
@@ -39,10 +40,32 @@ clear_internal_signals (sigset_t *set)
 {
 }
 
-typedef sigset_t internal_sigset_t;
-
 #define internal_sigemptyset(__s)            __sigemptyset (__s)
+#define internal_sigfillset(__s)             __sigfillset (__s)
 #define internal_sigaddset(__s, __i)         __sigaddset (__s, __i)
 #define internal_sigprocmask(__h, __s, __o)  __sigprocmask (__h, __s, __o)
 
+static inline void
+internal_signal_block_all (internal_sigset_t *oset)
+{
+  internal_sigset_t set;
+  internal_sigfillset (&set);
+  internal_sigprocmask (SIG_BLOCK, &set, oset);
+}
+
+static inline void
+internal_signal_restore_set (const internal_sigset_t *set)
+{
+  internal_sigprocmask (SIG_SETMASK, set, NULL);
+}
+
+static inline void
+internal_signal_unblock_signal (int sig)
+{
+  internal_sigset_t set;
+  internal_sigemptyset (&set);
+  internal_sigaddset (&set, sig);
+  internal_sigprocmask (SIG_UNBLOCK, &set, NULL);
+}
+
 #endif /* __INTERNAL_SIGNALS_H  */
diff --git a/sysdeps/generic/internal-sigset.h b/sysdeps/generic/internal-sigset.h
new file mode 100644
index 0000000..80279ff
--- /dev/null
+++ b/sysdeps/generic/internal-sigset.h
@@ -0,0 +1,26 @@
+/* Internal sigset_t definition.
+   Copyright (C) 2022-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _INTERNAL_SIGSET_H
+#define _INTERNAL_SIGSET_H
+
+#include <signal.h>
+
+typedef sigset_t internal_sigset_t;
+
+#endif