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

[Szabolcs Nagy]

The 10/07/2020 20:16, Florian Weimer wrote:
> * 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.

me too.

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