NetBSD Problem Report #56174

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Date: Sat, 15 May 2021 07:09:06 +0000 (UTC)
From: mforney@mforney.org
Reply-To: mforney@mforney.org
To: gnats-bugs@NetBSD.org
Subject: libcurses: __makewin() accesses uninitialized WINDOW field
X-Send-Pr-Version: www-1.0

>Number:         56174
>Category:       lib
>Synopsis:       libcurses: __makewin() accesses uninitialized WINDOW field
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    lib-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 15 07:10:01 +0000 2021
>Closed-Date:    Wed Jun 09 02:13:14 +0000 2021
>Last-Modified:  Wed Jun 09 05:15:01 +0000 2021
>Originator:     Michael Forney
>Release:        trunk
>Organization:
>Environment:
>Description:
I noticed the following warning when compiling libcurses/newwin.c:

In file included from libcurses/newwin.c:37:
libcurses/newwin.c: In function '__makenew':
libcurses/curses_private.h:89:29: warning: '*win.battr' may be used uninitialized [-Wmaybe-uninitialized]
   89 |         ((c).battr) = ((((c).battr) & WA_ATTRIBUTES ) | ((w) << WCW_SHIFT )); \
      |                         ~~~~^~~~~~~
libcurses/newwin.c:384:9: note: in expansion of macro 'SET_BGWCOL'
  384 |         SET_BGWCOL(*win, 1);
      |         ^~~~~~~~~~

I believe this warning is legitimate. The __makenew() function allocates the win structure, and then invokes the SET_BGWCOL macro without previously setting battr.

However, it looks like both callers of __makenew() overwrite the previous value of battr themselves. Additionally, I found no uses of the BGWCOL macro in the libcurses codebase.
>How-To-Repeat:
1. Compile libcurses/newwin.c with -Wall -O2.
2. Observe warning about use of uninitialized field.
>Fix:
If BGWCOL should be set on windows created with __newwin and __subwin, then __makenew() should initialize battr to 0 before invoking SET_BGWCOL, and __newwin/__subwin should take care to preserve it when setting battr.

I am not sure if this fix is correct, but my best attempt at a patch is the following:

diff --git a/lib/libcurses/newwin.c b/lib/libcurses/newwin.c
index 4db46cd..31cee08 100644
--- a/lib/libcurses/newwin.c
+++ b/lib/libcurses/newwin.c
@@ -135,9 +135,7 @@ __newwin(SCREEN *screen, int nlines, int ncols, int by, int bx, int ispad,

 	win->bch = ' ';
 	if (__using_color)
-		win->battr = __default_color;
-	else
-		win->battr = 0;
+		win->battr |= __default_color;
 	win->nextp = win;
 	win->ch_off = 0;
 	win->orig = NULL;
@@ -377,6 +375,7 @@ __makenew(SCREEN *screen, int nlines, int ncols, int by, int bx, int sub,
 	win->flags = (__IDLINE | __IDCHAR);
 	win->delay = -1;
 	win->wattr = 0;
+	win->battr = 0;
 #ifdef HAVE_WCHAR
 	win->bnsp = NULL;
 	SET_BGWCOL(*win, 1);

>Release-Note:

>Audit-Trail:
From: "Valeriy E. Ushakov" <uwe@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/56174 CVS commit: src/lib/libcurses
Date: Sat, 15 May 2021 11:06:08 +0000

 Module Name:	src
 Committed By:	uwe
 Date:		Sat May 15 11:06:08 UTC 2021

 Modified Files:
 	src/lib/libcurses: newwin.c

 Log Message:
 __newwin - fix BGWCOL initialization.

 From Michael Forney in PR lib/56174


 To generate a diff of this commit:
 cvs rdiff -u -r1.58 -r1.59 src/lib/libcurses/newwin.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->feedback
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Wed, 09 Jun 2021 00:48:08 +0000
State-Changed-Why:
is this fixed?


State-Changed-From-To: feedback->closed
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Wed, 09 Jun 2021 02:13:14 +0000
State-Changed-Why:
Feedback mail bounced.


From: Michael Forney <mforney@mforney.org>
To: gnats-bugs@netbsd.org
Cc: 
Subject: Re: lib/56174 (libcurses: __makewin() accesses uninitialized WINDOW field)
Date: Tue, 8 Jun 2021 20:26:26 -0700

 On 2021-06-08, dholland@netbsd.org <dholland@netbsd.org> wrote:
 > Synopsis: libcurses: __makewin() accesses uninitialized WINDOW field
 >
 > State-Changed-From-To: feedback->closed
 > State-Changed-By: dholland@NetBSD.org
 > State-Changed-When: Wed, 09 Jun 2021 02:13:14 +0000
 > State-Changed-Why:
 > Feedback mail bounced.

 Not sure which mail bounced (I did indeed receive the one asking for
 feedback). But, yes, this was fixed.

From: David Holland <dholland-bugs@netbsd.org>
To: gnats-bugs@netbsd.org
Cc: 
Subject: Re: lib/56174 (libcurses: __makewin() accesses uninitialized WINDOW
 field)
Date: Wed, 9 Jun 2021 05:10:23 +0000

 On Wed, Jun 09, 2021 at 03:30:02AM +0000, Michael Forney wrote:
  >  > Feedback mail bounced.
  >  
  >  Not sure which mail bounced (I did indeed receive the one asking for
  >  feedback). But, yes, this was fixed.

 Hrm. Not sure, went through dozens of bounces tonight, might have
 goofed.

 -- 
 David A. Holland
 dholland@netbsd.org

>Unformatted:

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