From: John Carter <redmine@...>
Date: 2009-05-15T17:41:16+09:00
Subject: [ruby-core:23460] [Bug #1472] rb_f_syscall converts string value to null terminated c string, but syscall structs can contain nulls.

Bug #1472: rb_f_syscall converts string value to null terminated c string, but syscall structs can contain nulls.
http://redmine.ruby-lang.org/issues/show/1472

Author: John Carter
Status: Open, Priority: Normal
ruby -v: ruby 1.8.7 (2009-04-08 patchlevel 160) [i686-linux]

The following snippet invokes the statfs64 syscall.
bug.rb================================================================
string = " "* 84
p syscall( 268, "/", string.size, string)
string = "\0"* 84
p syscall( 268, "/", string.size, string)
======================================================================

If I run this under ruby 1.8.6, both invocations work.

If I run this under ruby 1.8.7, the second one fails with...
ruby  -w bug.rb
0
bug.rb:4:in `syscall': string contains null byte (ArgumentError)
	from bug.rb:4

The reason is in ruby-1.8.7-p22/io.c in the function rb_f_syscall
there is this code....

	if (!NIL_P(v)) {
	    StringValue(v);
	    rb_str_modify(v);
	    arg[i] = (unsigned long)StringValueCStr(v);
	}

In ruby 1.8.6 is was 

	if (!NIL_P(v)) {
	    StringValue(v);
	    rb_str_modify(v);
	    arg[i] = (unsigned long)RSTRING(v)->ptr;
	}

The macro StringValueCStr is defined in ruby.h as....
  #define StringValueCStr(v) rb_string_value_cstr(&(v))

The function rb_string_value_cstr is defined in string.c as ....

rb_string_value_cstr(ptr)
    volatile VALUE *ptr;
{
    VALUE str = rb_string_value(ptr);
    char *s = RSTRING(str)->ptr;

    if (!s || RSTRING(str)->len != strlen(s)) {
	rb_raise(rb_eArgError, "string contains null byte");
    }
    return s;
}

I believe the original 1.8.6 implementation was correct and this
particular changed should be rolled back.

Thanks.

http://rubyforge.org/tracker/index.php?func=detail&aid=20895&group_id=426&atid=1698


Applies to 1.8.7 and 1.9.1 p 129


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