Bug 329641 - Possible to crash with SELinux relabeling support
Possible to crash with SELinux relabeling support
Product: Fedora
Classification: Fedora
Component: util-linux-ng (Show other bugs)
All Linux
low Severity low
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Assigned To: Karel Zak
Fedora Extras Quality Assurance
Depends On:
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Reported: 2007-10-12 11:52 EDT by KaiGai Kohei
Modified: 2007-11-30 17:12 EST (History)
1 user (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2007-10-22 05:01:13 EDT
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RHEL 7.3 requirements from Atomic Host:
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Attachments (Terms of Use)
The patch fixes the reported matter using matchpathcon() (939 bytes, patch)
2007-10-12 11:52 EDT, KaiGai Kohei
no flags Details | Diff

  None (edit)
Description KaiGai Kohei 2007-10-12 11:52:09 EDT
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 .
    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: %
                    program_name, device_name,
        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,
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.
Comment 1 KaiGai Kohei 2007-10-12 11:52:09 EDT
Created attachment 225681 [details]
The patch fixes the reported matter using matchpathcon()
Comment 2 Karel Zak 2007-10-22 05:01:13 EDT
This bugfix will be included in the next stable update (to v2.13.1). Thanks.

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