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From: Dimitry Andric <dim@FreeBSD.org>
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Subject: Re: svn commit: r328492 - head/contrib/opie/libopie
Date: Sat, 27 Jan 2018 23:31:11 +0100
In-Reply-To: <CABh_MKn=3pRWyMHUAQkG17dQVBFEwFA2esFixPtgkCt7VE5oCw@mail.gmail.com>
Cc: "Pedro F. Giffuni" <pfg@freebsd.org>,
 src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
To: Ed Schouten <ed@nuxi.nl>
References: <201801272216.w0RMGJwo057492@repo.freebsd.org>
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On 27 Jan 2018, at 23:20, Ed Schouten <ed@nuxi.nl> wrote:
> 
> 2018-01-27 23:16 GMT+01:00 Pedro F. Giffuni <pfg@freebsd.org>:
>>        char host[sizeof(utmp.ut_host) + 1];
>>        insecure = 1;
>> 
>> -       strncpy(host, utmp.ut_host, sizeof(utmp.ut_host));
>> -       host[sizeof(utmp.ut_host)] = 0;
>> +       strncpy(host, utmp.ut_host, sizeof(host));
> 
> Wait... This may access utmp.ut_host one byte past the end and no
> longer guarantees that host is null-terminated, right?

No, strncpy "copies at most len characters from src into dst".  However,
if the length of the source is equal to or greater than len, the
destination is *not* null terminated.  This is likely why the
"host[sizeof(utmp.ut_host)] = 0;" statement was added.

In any case, this is why strlcpy exists. :)

-Dimitry


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