Description of problem:

I found a theoretical crach in mkswap command with SELinux relabeling support.
See the following section. It is a part of util-linux-ng-2.13/disk-
utils/mkswap.c .
----------------
#ifdef HAVE_LIBSELINUX
    if (S_ISREG(statbuf.st_mode) && is_selinux_enabled()) {
        security_context_t context_string;
        security_context_t oldcontext;
        context_t newcontext;

        if ((fgetfilecon(DEV, &oldcontext) < 0) &&      <-- ATTENTION!
            (errno != ENODATA)) {
            fprintf(stderr, _("%s: %s: unable to obtain selinux file label: %
s\n"),
                    program_name, device_name,
                    strerror(errno));
            exit(1);
        }
        if (!(newcontext = context_new(oldcontext)))
            die(_("unable to create new selinux context"));
        if (context_type_set(newcontext, SELINUX_SWAPFILE_TYPE))
            die(_("couldn't compute selinux context"));

        context_string = context_str(newcontext);

        if (strcmp(context_string, oldcontext)!=0) {
            if (fsetfilecon(DEV, context_string)) {
                fprintf(stderr, _("%s: unable to relabel %s to %s: %s\n"),
                        program_name, device_name,
                        context_string,
                        strerror(errno));
                exit(1);
            }
        }
        context_free(newcontext);
        freecon(oldcontext);
    }
#endif
----------------
When fgetfilecon() is failed with -ENODATA, this process does not exit.
However, "oldcontext" is not initialized in this case,
so context_new() will be called with uninitialized "oldcontext" at the next.

Finally, it makes a segmentation fault, because context_new() have to refer an 
incorrect memory region.

Version-Release number of selected component (if applicable):
- util-linux-ng-2.13-2.fc8.src.rpm

The attached patch fixes this matter using matchpathcon().
If we cannot obtain actual file context due to -ENODATA, a context which is 
returned by matchpathcon() is applied as oldcontext.
Then, the type of the context is relabeled to "swapfile_t" explicitly.