libbsd setmode/getmode give unexpected mode_t value possibly due to uninitialised value

[RJVB]

Consider the following code from the implementation (InstallCmd()) of a Tcl extension function "xinstall" that mimics the /usr/bin/install command:

        case 'm': {
            if (!objc) {
                Tcl_WrongNumArgs(interp, 1, objv, "-m");
                return TCL_ERROR;
            }
            const char *modeString = Tcl_GetString(*(++objv));
            if (!(set = setmode(modeString))) {
                char errmsg[255];

                snprintf(errmsg, sizeof errmsg, "%s: error determining file mode %s: %s",
                     funcname, modeString, strerror(errno));
                Tcl_SetResult(interp, errmsg, TCL_VOLATILE);
                return TCL_ERROR;
            }
            mode = getmode(set, 0);
            if (verbose) {
                ui_debug(interp, "%s: mode=%s umask=0%o", funcname, modeString, mode);
            }
            free(set);
            objv++, objc -= 2;
            break;
        }

I use this function in a Tcl-based build/packaging/install system on KUbuntu 14.04 with kernel 4.8.15 .
When calling this as `xinstall -v -m 775 -d foo`there are intermittent conditions ("episodes") under which I see

```
:debug:destroot xinstall: mode=775 umask=0225
:error:destroot Failed to destroot qt5-kde-angel: error renaming "/opt/local/var/lnxports/build/_opt_local_site-ports_aqua_qt5-kde-angel/qt5-kde-angel/work/destroot/opt/local/libexec/qt5/lib/pkgconfig/Qt5X11Extras.pc" to "/opt/local/var/lnxports/build/_opt_local_site-ports_aqua_qt5-kde-angel/qt5-kde-angel/work/destroot/opt/local/lib/pkgconfig/Qt5X11Extras.pc": permission denied
```

and valgrind reports

```
==20578== 46 errors in context 11 of 13:
==20578== Conditional jump or move depends on uninitialised value(s)
==20578== at 0x77CD81C: getmode (setmode.c:123)
==20578== by 0x77D240B: InstallCmd (xinstall.c:254)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
==20578== by 0x4EB4F8A: TclExecuteByteCode (tclExecute.c:2414)
==20578== by 0x4EB8D6A: TclCompEvalObj (tclExecute.c:1535)
==20578== by 0x4E6FDE8: TclEvalObjEx (tclBasic.c:5296)
==20578== by 0x4EF2670: Tcl_UplevelObjCmd (tclProc.c:945)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
==20578== by 0x4EB4F8A: TclExecuteByteCode (tclExecute.c:2414)
==20578== by 0x4EF2F69: TclObjInterpProcCore (tclProc.c:1763)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
==20578== by 0x4EB4F8A: TclExecuteByteCode (tclExecute.c:2414)
==20578== Uninitialised value was created by a heap allocation
==20578== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20578== by 0x77CD93F: setmode (setmode.c:218)
==20578== by 0x77D23F5: InstallCmd (xinstall.c:246)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
==20578== by 0x4EB4F8A: TclExecuteByteCode (tclExecute.c:2414)
==20578== by 0x4EB8D6A: TclCompEvalObj (tclExecute.c:1535)
==20578== by 0x4E6FDE8: TclEvalObjEx (tclBasic.c:5296)
==20578== by 0x4EF2670: Tcl_UplevelObjCmd (tclProc.c:945)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
==20578== by 0x4EB4F8A: TclExecuteByteCode (tclExecute.c:2414)
==20578== by 0x4EF2F69: TclObjInterpProcCore (tclProc.c:1763)
==20578== by 0x4E6E2B5: TclEvalObjvInternal (tclBasic.c:3727)
```

This error tends to go away after having tried various approaches to avoid it, which hints at the effects of an uninitialised variable, or a bounds-overwrite, hence running the script through valgrind.

Ubuntu 14.04 is still at libbsd 0.6 so I backported the latest available packaging from Launchpad (0.8.3-1). Initial results are encouraging: valgrind no longer complains about setmode or getmode called from InstallCmd().

I'd like to urge you to provide an official backport of this package; the process is trivial (see my ppa:rjvbertin/misc archive).