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From: Florian Weimer <fw@deneb.enyo.de>
To: "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2] test-strnlen.c: Check that strnlen won't go beyond the
 maximum length
References: <20210327162449.3215538-1-hjl.tools@gmail.com>
 <87ft0g8oz4.fsf@mid.deneb.enyo.de>
 <CAMe9rOoZ1PtPWdFjEn0uU6BE2haG2frA=rmueYV4cOMk1hhpRw@mail.gmail.com>
Date: Sat, 27 Mar 2021 19:34:41 +0100
In-Reply-To: <CAMe9rOoZ1PtPWdFjEn0uU6BE2haG2frA=rmueYV4cOMk1hhpRw@mail.gmail.com>
 (H. J. Lu via Libc-alpha's message of "Sat, 27 Mar 2021 11:09:32
 -0700")
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* H. J. Lu via Libc-alpha:

> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Sat, 27 Mar 2021 09:06:39 -0700
> Subject: [PATCH v2] test-strnlen.c: Check that strnlen won't go beyond the
>  maximum length
>
> Place strings ending at page boundary without the null byte.  If an
> implementation goes beyond EXP_LEN, it will trigger the segfault.
> ---
>  string/test-strnlen.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/string/test-strnlen.c b/string/test-strnlen.c
> index 0293acbc71..d70faa26ab 100644
> --- a/string/test-strnlen.c
> +++ b/string/test-strnlen.c
> @@ -198,6 +198,35 @@ do_page_tests (void)
>      }
>  }
>  
> +/* Tests meant to unveil fail on implementations that access bytes
> +   beyond the maxium length.  */
> +
> +static void
> +do_page_2_tests (void)
> +{
> +  size_t i, exp_len, offset;
> +  size_t last_offset = page_size / sizeof (CHAR);
> +
> +  CHAR *s = (CHAR *) buf2;
> +  MEMSET (s, 65, last_offset);
> +
> +  /* Place short strings ending at page boundary without the null
> +     byte.  */
> +  offset = last_offset;
> +  for (i = 0; i < 128; i++)
> +    {
> +      /* Decrease offset to stress several sizes and alignments.  */
> +      offset--;
> +      exp_len = last_offset - offset;
> +      FOR_EACH_IMPL (impl, 0)
> +	{
> +	  /* If an implementation goes beyond EXP_LEN, it will trigger
> +	     the segfault.  */
> +	  do_one_test (impl, (CHAR *) (s + offset), exp_len, exp_len);
> +	}
> +    }
> +}

Thanks, looks good.  The comments and the commit message are much
clearer now.