[PATCH v2 02/14] stdio-common: Reject significands w/o digits in scanf [BZ #12701]

[Adhemerval Zanella Netto]

On 05/06/25 14:58, Maciej W. Rozycki wrote:
> From: Maciej W. Rozycki <macro@redhat.com>
> 
> Reject invalid formatted scanf real input data the significand part of 
> which is comprised of a hexadecimal prefix followed by a decimal point 
> only, optionally preceded by a sign.  Such data is a prefix of, but not 
> a matching input sequence and it is required by ISO C to cause a 
> matching failure.
> 
> Currently a matching success is instead incorrectly produced along with 
> the conversion result of zero, with data up to and including the decimal 
> point consumed from input.
> 
> Technically this change also causes lone . to be rejected early, though 
> it doesn't change semantics, because unlike 0x. it's not valid input to 
> 'strtod', etc. so it gets rejected at actual conversion time later on 
> anyway.
> 
> Test cases follow as separate changes.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
> No change from v1.
> ---
>  stdio-common/vfscanf-internal.c |   10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> glibc-scanf-bz12701-real-nodigit.diff
> Index: glibc/stdio-common/vfscanf-internal.c
> ===================================================================
> --- glibc.orig/stdio-common/vfscanf-internal.c
> +++ glibc/stdio-common/vfscanf-internal.c
> @@ -2561,15 +2561,15 @@ __vfscanf_internal (FILE *s, const char
>  	      goto errout;
>  	    }
>  
> -	  /* Have we read any character?  If we try to read a number
> -	     in hexadecimal notation and we have read only the `0x'
> -	     prefix this is an error.  Also it is an error where we
> -	     have read no digits after the exponent character.  */
> +	  /* Have we read any character?  If we try to read a number in
> +	     hexadecimal notation and we have read only the `0x' prefix,
> +	     this is an error.  Also it is an error where we have read
> +	     no digits (before or after the exponent character).  */
>  	  if (__glibc_unlikely (char_buffer_size (&charbuf) == got_sign
>  				|| ((flags & HEXA_FLOAT)
>  				    && (char_buffer_size (&charbuf)
>  					== 2 + got_sign)))
> -				|| (got_e && !got_digit))
> +				|| !got_digit)
>  	    conv_error ();
>  
>  	scan_float: