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From: Junio C Hamano <gitster@pobox.com>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: David Turner <dturner@twosigma.com>, git@vger.kernel.org, l.s.r@web.de
Subject: Re: [PATCH v3 2/2] xgethostname: handle long hostnames
Date: Tue, 18 Apr 2017 19:51:08 -0700	[thread overview]
Message-ID: <xmqq4lxlcdpf.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <20170419013552.GB28740@aiede.svl.corp.google.com> (Jonathan Nieder's message of "Tue, 18 Apr 2017 18:35:52 -0700")

Jonathan Nieder <jrnieder@gmail.com> writes:

> Hi,
>
> David Turner wrote:
>
>> If the full hostname doesn't fit in the buffer supplied to
>> gethostname, POSIX does not specify whether the buffer will be
>> null-terminated, so to be safe, we should do it ourselves.  Introduce
>> new function, xgethostname, which ensures that there is always a \0
>> at the end of the buffer.
>
> I think we should detect the error instead of truncating the hostname.
> That (on top of your patch) would look like the following.
>
> Thoughts?
> Jonathan
>
> diff --git i/wrapper.c w/wrapper.c
> index d837417709..e218bd3bef 100644
> --- i/wrapper.c
> +++ w/wrapper.c
> @@ -660,11 +660,13 @@ int xgethostname(char *buf, size_t len)
>  {
>  	/*
>  	 * If the full hostname doesn't fit in buf, POSIX does not
> -	 * specify whether the buffer will be null-terminated, so to
> -	 * be safe, do it ourselves.
> +	 * guarantee that an error will be returned. Check for ourselves
> +	 * to be safe.
>  	 */
>  	int ret = gethostname(buf, len);
> -	if (!ret)
> -		buf[len - 1] = 0;
> +	if (!ret && !memchr(buf, 0, len)) {
> +		errno = ENAMETOOLONG;
> +		return -1;
> +	}

Hmmmm.  "Does not specify if the buffer will be NUL-terminated"
would mean that it is OK for the platform gethostname() to stuff
sizeof(buf)-1 first bytes of the hostname in the buffer and then
truncate by placing '\0' at the end of the buf, and we would not
notice truncation with the above change on such a platform, no?

  reply	other threads:[~2017-04-19  2:51 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-18 21:57 [PATCH v3 0/2] gethostbyname fixes David Turner
2017-04-18 21:57 ` [PATCH v3 1/2] use HOST_NAME_MAX to size buffers for gethostname(2) David Turner
2017-04-19  1:28   ` Jonathan Nieder
2017-04-19  2:57     ` Junio C Hamano
2017-04-19 14:03     ` René Scharfe
2017-04-19 17:28     ` René Scharfe
2017-04-19 19:08       ` David Turner
2017-04-19 19:09       ` Torsten Bögershausen
2017-04-19 20:02         ` René Scharfe
2017-04-20 18:37           ` Torsten Bögershausen
2017-04-20 19:28             ` René Scharfe
2017-04-21  4:18               ` Torsten Bögershausen
2017-04-18 21:57 ` [PATCH v3 2/2] xgethostname: handle long hostnames David Turner
2017-04-19  1:35   ` Jonathan Nieder
2017-04-19  2:51     ` Junio C Hamano [this message]
2017-04-19 15:50       ` David Turner
2017-04-19 16:43         ` René Scharfe
2017-04-19  2:48   ` Junio C Hamano

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