do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp)
{
	struct task_struct *t = current;

	if (oss) {
		memset(oss, 0, sizeof(stack_t));
		oss->ss_sp = (void __user *) t->sas_ss_sp;
		oss->ss_size = t->sas_ss_size;
		oss->ss_flags = sas_ss_flags(sp) |
			(current->sas_ss_flags & SS_FLAG_BITS);
	}

	if (ss) {
		void __user *ss_sp = ss->ss_sp;
		size_t ss_size = ss->ss_size;
		unsigned ss_flags = ss->ss_flags;
		int ss_mode;

		if (unlikely(on_sig_stack(sp)))
			return -EPERM;

		ss_mode = ss_flags & ~SS_FLAG_BITS;
		if (unlikely(ss_mode != SS_DISABLE && ss_mode != SS_ONSTACK &&
				ss_mode != 0))
			return -EINVAL;

		if (ss_mode == SS_DISABLE) {
			ss_size = 0;
			ss_sp = NULL;
		} else {
			if (unlikely(ss_size < MINSIGSTKSZ))
				return -ENOMEM;
		}

		t->sas_ss_sp = (unsigned long) ss_sp;
		t->sas_ss_size = ss_size;
		t->sas_ss_flags = ss_flags;
	}
	return 0;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.