[Bug libc/12527] New: Off by one bug with ftell() with fmemopen()

["per.mathisen at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=12527

           Summary: Off by one bug with ftell() with fmemopen()
           Product: glibc
           Version: 2.12
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: per.mathisen@gmail.com


Created attachment 5269
  --> http://sourceware.org/bugzilla/attachment.cgi?id=5269
Program that fails

The attached tiny program assert fails on ftell(fp) == ftell(fp), which it
seems to me should always work. I only get this problem with file pointers
created with fmemopen and the "r+" mode, and only with sequences of events
similar to those in the attached file. The ftell() seems to always returns 1
less than the actual size when it fails.

There also seems to be an issue with fmemopen() when used with the "r+" mode if
the input buffer is not zero cleared. See comment in attachment.

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