[Bug stdio/25812] New: Libio vtable protection is sometimes only partially enforced

[Bug stdio/25812] New: Libio vtable protection is sometimes only partially enforced

[maxkamper at outlook dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

            Bug ID: 25812
           Summary: Libio vtable protection is sometimes only partially
                    enforced
           Product: glibc
           Version: 2.31
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: maxkamper at outlook dot com
  Target Milestone: ---

Some versions of GLIBC bundled with popular distros still place their libio
vtables in a writable segment. E.g. Ubuntu 1904 (which uses GLIBC 2.29)
exhibits this behaviour, whilst the earlier Ubuntu 1804 (which uses GLIBC 2.27)
does not.

This could be a choice on behalf of the distro maintainers but it seems
unlikely.

Vtable pointers are still checked before dereferencing but I feel this is
undermined somewhat by the fact that the vtables themselves are mapped
writable.

Perhaps the issue is in the Makerules file, around line 549, which is commented
"If the linker is good enough, we can let it use its default linker script."
The issue seems to manifest depending on the preceding ifeq statement's result.

I'm not well versed enough in the workings of linkers to comment as to why this
might be, but I've experienced the same writable vtable issue whilst building
GLIBC using more recent versions of GCC.

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[luciham20 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

Lucille F. Parham <luciham20 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luciham20 at gmail dot com

--- Comment #1 from Lucille F. Parham <luciham20 at gmail dot com> ---
This is a really interesting and informative post. Good job ! keep it up, hope
to read your other updates.
https://www.reddit.com/r/AndroidtoPCandMac/comments/f79k3w/how_to_easily_play_subway_surfers_in_pc/

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[luciham20 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

--- Comment #2 from Lucille F. Parham <luciham20 at gmail dot com> ---
This is a really interesting and informative post. Good job ! keep it up, hope
to read your other updates.
https://www.reddit.com/r/AndroidtoPCandMac/comments/f79k3w/how_to_easily_play_subway_surfers_in_pc/

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-04-11
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at sourceware dot org   |fweimer at redhat dot com
     Ever confirmed|0                           |1

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
I'm actively working on this.

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

--- Comment #4 from Florian Weimer <fweimer at redhat dot com> ---
Patch with test case posted:
https://sourceware.org/pipermail/libc-alpha/2022-April/137700.html

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[Bug stdio/25812] Libio vtable protection is sometimes only partially enforced

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25812

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-
   Target Milestone|---                         |2.36
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Florian Weimer <fweimer at redhat dot com> ---
Fixed for glibc 2.36 via:

commit 198abcbb94618730dae1b3f4393efaa49e0ec8c7
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon Apr 11 11:30:31 2022 +0200

    Default to --with-default-link=no (bug 25812)

    This is necessary to place the libio vtables into the RELRO segment.
    New tests elf/tst-relro-ldso and elf/tst-relro-libc are added to
    verify that this is what actually happens.

    The new tests fail on ia64 due to lack of (default) RELRO support
    inbutils, so they are XFAILed there.

I'm flagging this as security- because it is just a lack of intended hardening,
but not a vulnerability as such.

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