stdlib: Make abort AS-safe (BZ 26275) azanella/bz26275-abort-as

The recursive lock used on abort does not synchronize with 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 raise might create
programs with a non-expected signal mask.

To fix the AS-safe, the raise is issues without changing the process
signal mask, and an AS-safe lock is used if a SIGABRT is installed or
the process is blocked or ignored.  The the signal mask change removal,
there is no need to use a recursive lock.  The lock is also on
both _Fork and posix_spawn, to avoid the spawn process to see the
abort handler as SIG_DFL.

The posix_spawn possible issue is if caller sets a SIG_IGN for
SIGABRT, calls abort, and another thread issues posix_spawn just
after the sigaction returns.  With default options (not setting
POSIX_SPAWN_SETSIGDEF), the process can still see SIG_DFL for
SIGABRT, where it should be SIG_IGN.

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

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

0 files changed, 0 insertions, 0 deletions