[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[jackie.rosen at hushmail dot com]

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

Jackie Rosen <jackie.rosen at hushmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jackie.rosen at hushmail dot com

--- Comment #9 from Jackie Rosen <jackie.rosen at hushmail dot com> ---
*** Bug 260998 has been marked as a duplicate of this bug. ***
Seen from the domain http://volichat.com
Page where seen: http://volichat.com/adult-chat-rooms
Marked for reference. Resolved as fixed @bugzilla.

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[schwab at sourceware dot org]

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

Andreas Schwab <schwab at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|jackie.rosen at hushmail dot com   |

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[kees at outflux dot net]

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

Kees Cook <kees at outflux dot net> changed:

           What    |Removed                     |Added
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             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---

--- Comment #10 from Kees Cook <kees at outflux dot net> ---
I'd still like to have this patch applied -- while we can claim the behavior is
"undefined", it is not, in fact, undefined. It behaves one way without
-D_FORTIFY_SOURCE=2, and differently with it. And that difference doesn't need
to exist. Ubuntu carried this patch for quite a while.

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[schwab@linux-m68k.org]

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

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
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             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #11 from Andreas Schwab <schwab@linux-m68k.org> ---
The point of _FORTIFY_SOURCE is to expose undefined behaviour.

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[kees at outflux dot net]

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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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[siddhesh at redhat dot com]

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

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |siddhesh at redhat dot com

--- Comment #13 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
It might be a good idea to take this discussion to the libc-alpha mailing list.

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[lidaobing at gmail dot com]

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

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[kees at outflux dot net]

------- Additional Comments From kees at outflux dot net  2008-12-24 17:40 -------
Created an attachment (id=3625)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=3625&action=view)
work-around pre-trunc behavior

This patch restores the prior sprintf behavior.  Looking through
_IO_str_init_static_internal seems to indicate that nothing actually requires
"s" to lead with a NULL.  Is there anything wrong with this work-around, which
could be used until the number of affected upstream sources is not quite so
large?

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[mtk dot manpages at gmail dot com]

------- Additional Comments From mtk dot manpages at gmail dot com  2008-12-19 16:57 -------
(In reply to comment #6)
> I have submitted a patch for linux-manpages:
> http://thread.gmane.org/gmane.linux.man/639

I've applied the following patch for man-pages-3.16.

--- a/man3/printf.3
+++ b/man3/printf.3
@@ -133,6 +133,17 @@ string that specifies how subsequent arguments (or
arguments accessed via
 the variable-length argument facilities of
 .BR stdarg (3))
 are converted for output.
+
+C99 and POSIX.1-2001 specify that the results are undefined if a call to
+.BR sprintf (),
+.BR snprintf (),
+.BR vsprintf (),
+or
+.BR vsnprintf ()
+would cause to copying to take place between objects that overlap
+(e.g., if the target string array and one of the supplied input arguments
+refer to the same buffer).
+See NOTES.
 .SS "Return value"
 Upon successful return, these functions return the number of characters
 printed (not including the
@@ -851,6 +862,26 @@ and conversion characters \fBa\fP and \fBA\fP.
 glibc 2.2 adds the conversion character \fBF\fP with C99 semantics,
 and the flag character \fBI\fP.
 .SH NOTES
+Some programs imprudently rely on code such as the following
+
+    sprintf(buf, "%s some further text", buf);
+
+to append text to
+.IR buf .
+However, the standards explicitly note that the results are undefined
+if source and destination buffers overlap when calling
+.BR sprintf (),
+.BR snprintf (),
+.BR vsprintf (),
+and
+.BR vsnprintf ().
+.\" http://sourceware.org/bugzilla/show_bug.cgi?id=7075
+Depending on the version of
+.BR gcc (1)
+used, and the compiler options employed, calls such as the above will
+.B not
+produce the expected results.
+
 The glibc implementation of the functions
 .BR snprintf ()
 and


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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[pasky at suse dot cz]

------- Additional Comments From pasky at suse dot cz  2008-12-07 23:38 -------
I have submitted a patch for linux-manpages:
http://thread.gmane.org/gmane.linux.man/639

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[jakub at redhat dot com]

------- Additional Comments From jakub at redhat dot com  2008-12-07 22:56 -------
man 3p sprintf certainly documents it:
"If  copying  takes  place  between objects that overlap as a result of a call
to sprintf() or snprintf(), the results are undefined."

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[schwab at suse dot de]

------- Additional Comments From schwab at suse dot de  2008-12-07 19:05 -------
Then contact whoever wrote it.

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           What    |Removed                     |Added
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             Status|REOPENED                    |RESOLVED
         Resolution|                            |INVALID


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

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[kees at outflux dot net]

------- Additional Comments From kees at outflux dot net  2008-12-07 18:33 -------
Thanks for the clarification.  However, I think it is still a bug that the
limitation is not mentioned in the manpage.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |


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

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[schwab at suse dot de]

------- Additional Comments From schwab at suse dot de  2008-12-07 17:49 -------
sprintf(buf, "%sfoo", buf) is UNDEFINED.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


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

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[Bug libc/7075] sprintf(buf, "%sfoo", buf) has different results with -O2 -D_FORTIFY_SOURCE=2 (__sprintf_chk bug?)

[kees at outflux dot net]

------- Additional Comments From kees at outflux dot net  2008-12-07 17:42 -------
Created an attachment (id=3095)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=3095&action=view)
test case


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