Re: [Bugme-new] [Bug 9564] New: Uninitialzed variable fields cvt.h_margin and cvt.v_margin

On Fri, 14 Dec 2007 13:54:59 -0800 (PST)
bugme-daemon@bugzilla.kernel.org wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=9564

           Summary: Uninitialzed variable fields cvt.h_margin and
                    cvt.v_margin
           Product: Drivers
           Version: 2.5
     KernelVersion: 2.6.23
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(Other)
        AssignedTo: drivers_video-other@kernel-bugs.osdl.org
        ReportedBy: marciobuss@gmail.com


The errors can be found at drivers/video/fbcvt.c as follows:

(1) the test "if (margin)" at line 310 evaluates to false,
(2) this makes the test "if (cvt.flags & FB_CVT_FLAG_MARGINS)" at line 352
    to evaluate to false as well
(3) now cvt.h_margin is uninitialized at line 359, 368, and 370, and
    cvt.v_margin is uninitizalied at line 371.

In other words, both cvt.v_margin and cvt.h_margin are initialized conditinally
but used unconditionally. This bug is a false positive only if the parameter
"margins" at line 304 is never 0. However, this would make the test at line
310 unnecessary -- anyone looking at the code is miled into believing that
0 is a legal value for "margins". This means the code does require some change
in my humble opinion.

Could someone please take a look at this?

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[Andrew Morton - Fri, Jan 18, 2008 at 02:00:55PM -0800]
| On Fri, 14 Dec 2007 13:54:59 -0800 (PST)
| bugme-daemon@bugzilla.kernel.org wrote:
| 
| > http://bugzilla.kernel.org/show_bug.cgi?id=9564
| > 
| >            Summary: Uninitialzed variable fields cvt.h_margin and
| >                     cvt.v_margin
| >            Product: Drivers
| >            Version: 2.5
| >      KernelVersion: 2.6.23
| >           Platform: All
| >         OS/Version: Linux
| >               Tree: Mainline
| >             Status: NEW
| >           Severity: normal
| >           Priority: P1
| >          Component: Video(Other)
| >         AssignedTo: drivers_video-other@kernel-bugs.osdl.org
| >         ReportedBy: marciobuss@gmail.com
| > 
| > 
| > The errors can be found at drivers/video/fbcvt.c as follows:
| > 
| > (1) the test "if (margin)" at line 310 evaluates to false,
| > (2) this makes the test "if (cvt.flags & FB_CVT_FLAG_MARGINS)" at line 352
| >     to evaluate to false as well
| > (3) now cvt.h_margin is uninitialized at line 359, 368, and 370, and
| >     cvt.v_margin is uninitizalied at line 371.
| > 
| > In other words, both cvt.v_margin and cvt.h_margin are initialized conditinally
| > but used unconditionally. This bug is a false positive only if the parameter
| > "margins" at line 304 is never 0. However, this would make the test at line
| > 310 unnecessary -- anyone looking at the code is miled into believing that
| > 0 is a legal value for "margins". This means the code does require some change
| > in my humble opinion.
| > 
| 
| Could someone please take a look at this?

unfortunelly, it's not really obvious what is the right way of
calculation. *should* the 1.8% margin be involved in calculation
all the time or 0 is legal too?

		- Cyrill -