[PATCH] D20334: [libcxx] Fix a bug in strstreambuf::overflow

[Duncan P. N. Exon Smith via cfe-commits]

The fix looks fairly obvious, but you haven't added a testcase.  Would you please do so?

> On 2016-May-17, at 12:20, Akira Hatanaka via cfe-commits <cfe-commits at lists.llvm.org> wrote:
> 
> ahatanak created this revision.
> ahatanak added reviewers: mclow.lists, EricWF, howard.hinnant.
> ahatanak added a subscriber: cfe-commits.
> 
> The end pointer should point to one past the end of the newly allocated buffer.
> 
> Without this fix, asan reports an error when the following code is compiled and executed:
> 
> $ cat test.cpp
> 
> ```
> std::string stringOfLength(const size_t length) {
>  std::string s("");
> 
>  std::string characters("abcdefghijklmnopqrstuvwxyz0123456789+-*/");
>  for (size_t i = 0; i < length; ++i) {
>    s += characters[i % characters.size()];
>  }
> 
>  return s;
> }
> 
> int main(int, char const **argv) {
>  std::ostrstream oss;
> 
>  oss << stringOfLength(atoi(argv[1])) << std::ends;
>  std::cout << oss.str();
>  oss.freeze(false);
> 
>  return 0;
> }```
> 
> $ clang++  -fsanitize=address test.cpp && ./a.out 4096
> ==18970==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62100001dd00 at pc 0x00010277c45d bp 0x7fff5d4ce6e0 sp 0x7fff5d4cdea0
> READ of size 4097 at 0x62100001dd00 thread T0
>    #0 0x10277c45c in wrap_strlen (libclang_rt.asan_osx_dynamic.dylib+0x4345c)
>    #1 0x102733954 in std::__1::char_traits<char>::length(char const*) (a.out+0x100002954)
>    #2 0x10273390b in std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<<<std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*) (a.out+0x10000290b)
>    #3 0x102733346 in main (a.out+0x100002346)
>    #4 0x7fff901905ac in start (libdyld.dylib+0x35ac)
>    #5 0x1  (<unknown module>)
> 
> 0x62100001dd00 is located 0 bytes to the right of 4096-byte region [0x62100001cd00,0x62100001dd00)
> allocated by thread T0 here:
>    #0 0x10278d42b in wrap__Znam (libclang_rt.asan_osx_dynamic.dylib+0x5442b)
>    #1 0x7fff9bdc9fa1 in std::__1::strstreambuf::overflow(int) (libc++.1.dylib+0x44fa1)
>    #2 0x7fff9bd901cc in std::__1::basic_streambuf<char, std::__1::char_traits<char> >::xsputn(char const*, long) (libc++.1.dylib+0xb1cc)
>    #3 0x10273547c in std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> > std::__1::__pad_and_output<char, std::__1::char_traits<char> >(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char> >, char const*, char const*, char const*, std::__1::ios_base&, char) (a.out+0x10000447c)
>    #4 0x102734312 in std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) (a.out+0x100003312)
>    #5 0x10273389d in std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<<<char, std::__1::char_traits<char>, std::__1::allocator<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) (a.out+0x10000289d)
>    #6 0x1027332c4 in main (a.out+0x1000022c4)
>    #7 0x7fff901905ac in start (libdyld.dylib+0x35ac)
>    #8 0x1  (<unknown module>)
> 
> http://reviews.llvm.org/D20334
> 
> Files:
>  src/strstream.cpp
> 
> Index: src/strstream.cpp
> ===================================================================
> --- src/strstream.cpp
> +++ src/strstream.cpp
> @@ -180,7 +180,7 @@
>                 delete [] eback();
>         }
>         setg(buf, buf + ninp, buf + einp);
> -        setp(buf + einp, buf + einp + eout);
> +        setp(buf + einp, buf + new_size);
>         pbump(static_cast<int>(nout));
>         __strmode_ |= __allocated;
>     }
> 
> 
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