Re: sigaction's ucontext_t with incorrect stack reference when SA_SIGINFO is being used ?

[Xavier Roche <roche+kml2@exalead.com>]

Nicholas Miell wrote:
> so if uc_stack doesn't point to the stack in use immediately prior to
> signal generation, this is a bug.

Looking at arch/i386/kernel/signal.c (and others) inside
setup_rt_frame(), the problem is pretty obvious:

err |= __put_user(current->sas_ss_sp, &frame_user->uc.uc_stack.ss_sp);
err |= __put_user(sas_ss_flags(regs->esp),
	&frame->uc.uc_stack.ss_flags);
err |= __put_user(current->sas_ss_size, &frame_user->uc.uc_stack.ss_size);

And of course, the ss_sp is NULL when no alternative stack is used.
Seems definitively a bug.

However, my reading of include/linux/sched.h and thread_info.h did not
enlighten me on the way to get the original thread's stack base and size.