Hi Thomas, thanks for reviewing.
The test has also passed our internal testing. I'll run it through jdk-submit and then push it in the course of the day. Best regards Christoph > -----Original Message----- > From: Thomas Stüfe [mailto:thomas.stu...@gmail.com] > Sent: Freitag, 27. April 2018 18:15 > To: Langer, Christoph <christoph.lan...@sap.com> > Cc: vyom tewari <vyom.tew...@oracle.com>; net-dev@openjdk.java.net; > Brian Burkhalter <brian.burkhal...@oracle.com> > Subject: Re: RFR(XS): 8202181: Correctly specify size of hostname buffer in > Unix Inet*AddressImpl_getLocalHostName implementations > > Hi Christoph, > > On Fri, Apr 27, 2018 at 9:35 AM, Langer, Christoph > <christoph.lan...@sap.com> wrote: > > Hi all, > > > > thanks for looking into this. Here are a few comments > > > > First of all, there are no real life issues I have seen with this. It is > > just > something that occurred to me when working with the code. But, why not fix > it, even it is a corner case that might never happen. > > > > @Thomas: As for the zero termination of the hostname result after the call > to gethostname: Yes, we should unconditionally terminate the result, which > we do. Unfortunately this part of code cannot be moved outside the solaris > #ifdef because the part in the #ifdef contains variable declarations. And you > know - the C compatibility issue... > > > > Ok. > > > I looked again into the macro definitions for for HOST_NAME_MAX and > NI_MAXHOST. HOST_NAME_MAX is mentioned in the gethostname docs > ([1] and [2]). Glibc docs indicate it is 64 Byte or 255 Byte. So it looks > like it is a > quite small buffer, compared to NI_MAXHOST from netdb.h, which is the > value that getnameinfo likes to work with, as per [3]. Posix genameinfo doc > ([4]) does not mention NI_MAXHOST but Linux doc says it is 1025 which is > what we'd define if it is not set. > > > > Okay, thanks for the research! This is weird, why two different > defines for the same thing. > > The only (probably highly theoretical) problem I see is that there may > be platforms which do not define NI_MAXHOST but where > HOST_MAX_NAME is > defined and larger than 1025 char sized output buffers. Then, we would > artificially limit ourselves to 1025 characters. (Was Matthias not > working on a problem with truncated host names in our hpux port?). > > One could in theory solve this by falling back to HOST_MAX_NAME if > NI_MAXHOST is undefined: > > #ifdnef NI_MAXHOST > #ifdef HOST_MAX_NAME > #define NI_MAXHOST HOST_MAX_NAME > #else > #define NI_MAXHOST 1025 > #endif > #endif > > However, I am fine with your current patch. I think redefinition of > NI_MAXHOST - if even necessary - should be done in a follow up issue. > > > Taking this input I have updated my webrev to round things up a little bit: > http://cr.openjdk.java.net/~clanger/webrevs/8202181.1/ > > > > I moved the definition of NI_MAXHOST into net_util_md.h and updated > the comment a little bit to make clearer why it is there. In > Inet4AddressImpl.c > and Inet6AddressImpl.c I also fixed the other places where getnameinfo is > called to use sizeof(buffer) instead of NI_MAXHOST. > > > > All looks well. Again, thanks for the research. > > ... Thomas > > > Best regards > > Christoph > > > > [1] http://man7.org/linux/man-pages/man2/gethostname.2.html > > [2] > http://pubs.opengroup.org/onlinepubs/009695399/functions/gethostname. > html > > [3] http://man7.org/linux/man-pages/man3/getnameinfo.3.html > > [4] > http://pubs.opengroup.org/onlinepubs/9699919799/functions/getnameinfo. > html > > > > > >> -----Original Message----- > >> From: vyom tewari [mailto:vyom.tew...@oracle.com] > >> Sent: Freitag, 27. April 2018 08:38 > >> To: Thomas Stüfe <thomas.stu...@gmail.com> > >> Cc: Langer, Christoph <christoph.lan...@sap.com>; net- > >> d...@openjdk.java.net > >> Subject: Re: RFR(XS): 8202181: Correctly specify size of hostname buffer in > >> Unix Inet*AddressImpl_getLocalHostName implementations > >> > >> > >> > >> On Friday 27 April 2018 10:58 AM, Thomas Stüfe wrote: > >> > On Fri, Apr 27, 2018 at 5:57 AM, vyom tewari > <vyom.tew...@oracle.com> > >> wrote: > >> >> Hi Christoph, > >> >> > >> >> > >> >> On Tuesday 24 April 2018 04:45 PM, Langer, Christoph wrote: > >> >> > >> >> Hi Vyom, > >> >> > >> >> I think, it is intentional to handle case where return "hostname" is to > >> >> large to > >> >> fit in array. if you see the man page(http://man7.org/linux/man- > >> >> pages/man2/gethostname.2.html) it says that it is unspecified > whether > >> >> returned buffer includes a terminating null byte. > >> >> > >> >> current code will put null in case of large "hostname", What do you > think ? > >> >> > >> >> yes, I had read the man page and saw this point of the spec. But > exactly > >> for > >> >> this purpose there's this code: > >> >> > >> >> // make sure string is null-terminated > >> >> hostname[NI_MAXHOST] = '\0'; > >> >> > >> >> If we only hand 'NI_MAXHOST' as size value into gethostname, then > the > >> >> function might only write NI_MAXHOST - 1 characters of the hostname > >> into the > >> >> buffer. > >> >> > >> >> doc says it will copy len bytes into buffer and will not copy null > character > >> >> into the buffer. > >> >> > >> >> ################################ > >> >> > >> >> C library/kernel differences > >> >> The GNU C library does not employ the gethostname() system call; > >> >> instead, it implements gethostname() as a library function that > >> >> calls > >> >> uname(2) and copies up to len bytes from the returned nodename > >> field > >> >> into name. Having performed the copy, the function then checks > >> >> if > >> >> the length of the nodename was greater than or equal to len, and > if > >> >> it is, then the function returns -1 with errno set to > ENAMETOOLONG; > >> >> in this case, a terminating null byte is not included in the > >> >> returned > >> >> name. > >> >> > >> > ########################################################## > >> ## > >> >> > >> > This is shared code, so we should refer to Posix, not linux specific man > >> pages. > >> > > >> > > >> > http://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostname > >> .html > >> > > >> > <quote> > >> > > >> > DESCRIPTION > >> > > >> > The gethostname() function shall return the standard host name for the > >> > current machine. The namelen argument shall specify the size of the > >> > array pointed to by the name argument. The returned name shall be > >> > null-terminated, except that if namelen is an insufficient length to > >> > hold the host name, then the returned name shall be truncated and it > >> > is unspecified whether the returned name is null-terminated. > >> > > >> > Host names are limited to {HOST_NAME_MAX} bytes. > >> > > >> > RETURN VALUE > >> > > >> > Upon successful completion, 0 shall be returned; otherwise, -1 shall > >> > be returned. > >> > > >> > </quote> > >> > > >> > Note that there is no indication what happens if the buffer is too > >> > small. It may zero-terminate, it may not. It may return an error, it > >> > may not. Decision is left to the platform implementors. > >> > > >> > So from that, I would pass in a large-enough buffer and always > >> > zero-terminate on success. According to Posix, a large-enough buffer > >> > means HOST_NAME_MAX bytes. > >> > > >> > I do not understand why we use NI_MAXHOST instead (and we we > define > >> it > >> > to an arbitrary 1025 byte if undefined). Were there platforms where > >> > HOST_NAME_MAX was too short? If yes, one should at least check that > >> > NI_MAXHOST >= HOST_NAME_MAX. > >> Even i noticed this, why we use our own NI_MAXHOST instead > >> HOST_NAME_MAX ? > >> >> Just for curiosity, are we facing any issues with the current code ?. > >> >> Your > >> >> code change looks logical but if nothing is broken then why to change > >> code. > >> >> > >> > If it can be proven by looking at the API description that it is > >> > broken for some corner case, why keep it broken? > >> :) Agreed, as i said Christoph change is logically correct but i > >> don't know the history behind current code, so just wanted to be sure > >> that we are not missing any corner case. > >> > >> Thanks, > >> Vyom > >> > >> > > >> > Thanks, Thomas > >> > > >> >> Thanks, > >> >> Vyom > >> >> > >> >> Best regards > >> >> Christoph > >> >> > >> >> > >
