gethostbyname buffer overflow (glibc)

gethostbyname buffer overflow (glibc)

[Daniel Cegiełka]

eg from:

http://www.openwall.com/lists/oss-security/2015/01/27/9

# gcc ghost.c && ./a.out
should not happen


  retval = gethostbyname_r(name, &resbuf, temp.buffer,
sizeof(temp.buffer), &result, &herrno);

  if (strcmp(temp.canary, CANARY) != 0) {
    puts("vulnerable");
    exit(EXIT_SUCCESS);
  }
  if (retval == ERANGE) {
    puts("not vulnerable");
    exit(EXIT_SUCCESS);
  }
  puts("should not happen");
  exit(EXIT_FAILURE);

Double exit. Is something wrong with gethostbyname_r() in musl?

Daniel

Re: gethostbyname buffer overflow (glibc)

[Rich Felker]

On Tue, Jan 27, 2015 at 05:59:36PM +0100, Daniel Cegiełka wrote:
> eg from:
> 
> http://www.openwall.com/lists/oss-security/2015/01/27/9
> 
> # gcc ghost.c && ./a.out
> should not happen
> 
> 
>   retval = gethostbyname_r(name, &resbuf, temp.buffer,
> sizeof(temp.buffer), &result, &herrno);
> 
>   if (strcmp(temp.canary, CANARY) != 0) {
>     puts("vulnerable");
>     exit(EXIT_SUCCESS);
>   }
>   if (retval == ERANGE) {
>     puts("not vulnerable");
>     exit(EXIT_SUCCESS);
>   }
>   puts("should not happen");
>   exit(EXIT_FAILURE);
> 
> Double exit. Is something wrong with gethostbyname_r() in musl?

I'm not sure what you mean by "double exit". As far as I can tell,
musl just detects errors in a different order, and returns ENOENT (2)
rather than ERANGE because the name is not valid.

Rich

Re: gethostbyname buffer overflow (glibc)

[Daniel Cegiełka]

2015-01-27 18:10 GMT+01:00 Rich Felker <dalias@libc.org>:
> On Tue, Jan 27, 2015 at 05:59:36PM +0100, Daniel Cegiełka wrote:
>> eg from:
>>
>> http://www.openwall.com/lists/oss-security/2015/01/27/9
>>
>> # gcc ghost.c && ./a.out
>> should not happen
>>
>>
>>   retval = gethostbyname_r(name, &resbuf, temp.buffer,
>> sizeof(temp.buffer), &result, &herrno);
>>
>>   if (strcmp(temp.canary, CANARY) != 0) {
>>     puts("vulnerable");
>>     exit(EXIT_SUCCESS);
>>   }
>>   if (retval == ERANGE) {
>>     puts("not vulnerable");
>>     exit(EXIT_SUCCESS);
>>   }
>>   puts("should not happen");
>>   exit(EXIT_FAILURE);
>>
>> Double exit. Is something wrong with gethostbyname_r() in musl?
>
> I'm not sure what you mean by "double exit".

ghost.c return EXIT_FAILURE instead EXIT_SUCCESS, which is checked in
two cases (only)...

> As far as I can tell,
> musl just detects errors in a different order, and returns ENOENT (2)
> rather than ERANGE because the name is not valid.

... and yes, ghost.c should also check the other errors.

thx

> Rich