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Date:   Tue, 05 Oct 2021 14:30:57 +0200
From:   Thomas Gleixner <>
To:     "Chang S. Bae" <>,,,,
Subject: Re: [PATCH v11 16/29] x86/fpu/xstate: Support both legacy and
 expanded signal XSTATE size

On Fri, Oct 01 2021 at 15:37, Chang S. Bae wrote:
>  static int
>  do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
>  		size_t min_ss_size)
> @@ -4187,6 +4192,9 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
>  				return -ENOMEM;
>  		}
> +		if (!arch_enough_sigaltstack(t, ss_size))
> +			return -EINVAL;
> +

How is this even remotely correct?


  To disable an existing stack, specify ss.ss_flags as SS_DISABLE.  In
  this case, the kernel ignores any other flags in ss.ss_flags and the
  remaining fields in ss.

So for SS_DISABLE ss_size can be legitimately 0 or any other random
number smaller than the required stack.

The min_ss_minsize check is conditional for this very reason.



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