Re: [PATCH] stdio: fix vfscanf with matches longer than INT_MAX (bug 27650)

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

* Alyssa Ross:

> I have not done a copyright assignment yet, but I think this change
> should be small enough to be exempt?

Yes, I think it's small enough.

The test case wouldn't be, though.  I think the one on the bug needs
some large (infinite) input on the stdin, though.  A real test case
for glibc should probably involve pipe, fork, and fdopen.  fopencookie
could work, too.

>  stdio-common/vfscanf-internal.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
> index 38e74776a5..1d81e16f4e 100644
> --- a/stdio-common/vfscanf-internal.c
> +++ b/stdio-common/vfscanf-internal.c
> @@ -2479,11 +2479,6 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  	  else
>  	    not_in = 0;
>  
> -	  if (width < 0)
> -	    /* There is no width given so there is also no limit on the
> -	       number of characters we read.  Therefore we set width to
> -	       a very high value to make the algorithm easier.  */
> -	    width = INT_MAX;
>  
>  #ifdef COMPILE_WSCANF
>  	  /* Find the beginning and the end of the scanlist.  We are not
> @@ -2647,7 +2642,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  			}
>  		    }
>  		}
> -	      while (--width > 0 && inchar () != WEOF);
> +	      while ((width < 0 || --width > 0) && inchar () != WEOF);
>  	    out:
>  #else
>  	      char buf[MB_LEN_MAX];
> @@ -2732,7 +2727,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  			}
>  		    }
>  
> -		  if (--width <= 0)
> +		  if (width >= 0 && --width <= 0)
>  		    break;
>  		}
>  	      while (inchar () != EOF);
> @@ -2884,7 +2879,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  		  assert (n <= MB_LEN_MAX);
>  		  str += n;
>  		}
> -	      while (--width > 0 && inchar () != WEOF);
> +	      while ((width < 0 || --width > 0) && inchar () != WEOF);
>  	    out2:
>  #else
>  	      do
> @@ -2938,7 +2933,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  			}
>  		    }
>  		}
> -	      while (--width > 0 && inchar () != EOF);
> +	      while ((width < 0 || --width > 0) && inchar () != EOF);
>  #endif
>  
>  	      if (__glibc_unlikely (now == read_in))

So I tried to review this.  -U100 helped.  I was worried about width
starting out as positive and going negative.  But as far as I can
tell, processing stops once width == 0, so the issue cannot happen.

Do you want to work on the test case?  Will the copyright assignment
be an obstacle?