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From: "kees at outflux dot net" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)
Date: Fri, 13 Jun 2014 20:36:00 -0000	[thread overview]
Message-ID: <bug-7075-131-8bQlnlly6y@http.sourceware.org/bugzilla/> (raw)
In-Reply-To: <bug-7075-131@http.sourceware.org/bugzilla/>

https://sourceware.org/bugzilla/show_bug.cgi?id=7075

--- Comment #12 from Kees Cook <kees at outflux dot net> ---
It's not defined in POSIX, but it has worked a certain way in glibc for
decades. There's no _reason_ to break it for _FORTIFY_SOURCE. Pre-truncating
just silently breaks programs and does weird stuff. If you want to expose it
with _FORITFY_SOURCE then have vsprintf notice that the target and first format
argument are the same variable, and refuse to build.

Either pretruncation should be eliminated, or the undefined behavior should be
explicitly detected and dealt with. Just having programs lose data while
running with no indication of the cause seems like a terrible user experience.

-- 
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  parent reply	other threads:[~2014-06-13 20:36 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-7075-131@http.sourceware.org/bugzilla/>
2014-02-16 17:44 ` jackie.rosen at hushmail dot com
2014-05-28 19:42 ` schwab at sourceware dot org
2014-06-13 19:49 ` kees at outflux dot net
2014-06-13 20:25 ` schwab@linux-m68k.org
2014-06-13 20:36 ` kees at outflux dot net [this message]
2014-06-13 20:48 ` siddhesh at redhat dot com
2014-06-16 10:57 ` fweimer at redhat dot com
2008-12-07 17:43 [Bug libc/7075] New: " kees at outflux dot net
2008-12-07 17:44 ` [Bug libc/7075] " kees at outflux dot net
2008-12-07 17:52 ` schwab at suse dot de
2008-12-07 18:36 ` kees at outflux dot net
2008-12-07 19:08 ` schwab at suse dot de
2008-12-07 22:57 ` jakub at redhat dot com
2008-12-07 23:39 ` pasky at suse dot cz
2008-12-19 16:58 ` mtk dot manpages at gmail dot com
2008-12-24 17:41 ` kees at outflux dot net
2009-02-05  8:55 ` lidaobing at gmail dot com

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