Hello All,

   In reviewing code in directory Python-3.4.3/Modules, file 
'mmapmodule', I found a call to 'lseek()' without a check for
a return value of -1, indicating failure.  The patch file below
corrects this issue (diff -u format):

--- mmapmodule.c.orig	2015-04-02 19:05:30.380554538 -0700
+++ mmapmodule.c	2015-04-02 19:11:00.320488207 -0700
@@ -1335,7 +1335,11 @@
             return NULL;
         }
         /* Win9x appears to need us seeked to zero */
-        lseek(fileno, 0, SEEK_SET);
+	if (lseek(fileno, 0, SEEK_SET) == -1) { /* call to lseek() failed */
+	    PyErr_SetFromErrno(PyExc_OSError);
+	    return NULL;
+	}
+
     }
 
     m_obj = (mmap_object *)type->tp_alloc(type, 0);

I am attaching the patch file to this bug report...

Thanks for the patch, Bill. If you want to work on similar issues see also issue 15948.

I would check 23855 as well, since the malloc() missing a sanity check,
which could be a more serious issue ..

On Sat, Apr 4, 2015 at 1:32 AM, Berker Peksag <report@bugs.python.org>
wrote:

>
> Berker Peksag added the comment:
>
> Thanks for the patch, Bill. If you want to work on similar issues see also
> issue 15948.
>
> ----------
> components: +Extension Modules -Interpreter Core
> nosy: +berker.peksag, haypo, serhiy.storchaka
> stage:  -> patch review
> versions: +Python 3.5
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue23860>
> _______________________________________
>

>  /* Win9x appears to need us seeked to zero */
>  lseek(fileno, 0, SEEK_SET);

Hum, is it still needed in 2015 with Python 3.5? We even dropped support for Windows XP.

At the moment, I'm not sure if it's needed or not, but if it's only an
issue with XP, then it might not be worth fixing...:)

On Thu, Apr 9, 2015 at 1:35 PM, STINNER Victor <report@bugs.python.org>
wrote:

>
> STINNER Victor added the comment:
>
> >  /* Win9x appears to need us seeked to zero */
> >  lseek(fileno, 0, SEEK_SET);
>
> Hum, is it still needed in 2015 with Python 3.5? We even dropped support
> for Windows XP.
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue23860>
> _______________________________________
>

"At the moment, I'm not sure if it's needed or not, but if it's only an
issue with XP, then it might not be worth fixing...:)"

If the workaround is no longer needed, the lseek() call should be removed.

Oh right, PR 7017 does that: it removes the lseek() call ;-)