Re: [PATCH] Fix aliasing violation in __vfscanf_internal [BZ #26690]

[Florian Weimer <fw@deneb.enyo.de>]

* Adhemerval Zanella:

> On 07/10/2020 15:08, Florian Weimer wrote:
>> * Szabolcs Nagy via Libc-alpha:
>> 
>>> diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
>>> index 95b46dcbeb..d832493623 100644
>>> --- a/stdio-common/vfscanf-internal.c
>>> +++ b/stdio-common/vfscanf-internal.c
>>> @@ -135,6 +135,16 @@
>>>  
>>>  #include "printf-parse.h" /* Use read_int.  */
>>>  
>>> +/* Same as read_int, but for CHAR_T * instead of UCHAR_T * string.  */
>>> +static int
>>> +read_int_char (const CHAR_T * *pstr)
>>> +{
>>> +  const UCHAR_T *ustr = (const UCHAR_T *) *pstr;
>>> +  int retval = read_int (&ustr);
>>> +  *pstr = (const CHAR_T *) ustr;
>>> +  return retval;
>>> +}
>>> +
>>>  #define encode_error() do {						      \
>>>  			  __set_errno (EILSEQ);				      \
>>>  			  goto errout;					      \
>>> @@ -486,7 +496,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>>>        /* Check for a positional parameter specification.  */
>>>        if (ISDIGIT ((UCHAR_T) *f))
>>>  	{
>>> -	  argpos = read_int ((const UCHAR_T **) &f);
>>> +	  argpos = read_int_char (&f);
>>>  	  if (*f == L_('$'))
>>>  	    ++f;
>>>  	  else
>>> @@ -522,7 +532,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>>>        /* Find the maximum field width.  */
>>>        width = 0;
>>>        if (ISDIGIT ((UCHAR_T) *f))
>>> -	width = read_int ((const UCHAR_T **) &f);
>>> +	width = read_int_char (&f);
>>>      got_width:
>>>        if (width == 0)
>>>  	width = -1;
>> 
>> Patch and commit message look reasonable to me.  Thanks.
>> 
>
> Andreas has sent a similar fix for the same issue [1]. Is it something
> wrong with his fix? It seems to cover more aliasing violation 
>
> [1] https://sourceware.org/pipermail/libc-alpha/2020-October/118149.html

The other patch looks reasonable to me as well, slightly better even.
I had missed it, sorry.

The additional changes are just shuffling harmless casts around, not
fixes for more aliasing violations, as far as I can see.