CVE-2024-27406: lib/Kconfig.debug: TEST_IOV_ITER depends on MMU

CVE-2024-27406: lib/Kconfig.debug: TEST_IOV_ITER depends on MMU

[Greg Kroah-Hartman]

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

lib/Kconfig.debug: TEST_IOV_ITER depends on MMU

Trying to run the iov_iter unit test on a nommu system such as the qemu
kc705-nommu emulation results in a crash.

    KTAP version 1
    # Subtest: iov_iter
    # module: kunit_iov_iter
    1..9
BUG: failure at mm/nommu.c:318/vmap()!
Kernel panic - not syncing: BUG!

The test calls vmap() directly, but vmap() is not supported on nommu
systems, causing the crash.  TEST_IOV_ITER therefore needs to depend on
MMU.

The Linux kernel CVE team has assigned CVE-2024-27406 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.6 with commit 2d71340ff1d4 and fixed in 6.6.19 with commit e6316749d603
	Issue introduced in 6.6 with commit 2d71340ff1d4 and fixed in 6.7.7 with commit 9e6e541b9776
	Issue introduced in 6.6 with commit 2d71340ff1d4 and fixed in 6.8 with commit 1eb1e984379e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-27406
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	lib/Kconfig.debug


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e6316749d603fe9c4c91f6ec3694e06e4de632a3
	https://git.kernel.org/stable/c/9e6e541b97762d5b1143070067f7c68f39a408f8
	https://git.kernel.org/stable/c/1eb1e984379e2da04361763f66eec90dd75cf63e

Re: CVE-2024-27406: lib/Kconfig.debug: TEST_IOV_ITER depends on MMU

[Michal Koutný]

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On Fri, May 17, 2024 at 01:40:41PM GMT, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> BUG: failure at mm/nommu.c:318/vmap()!
> Kernel panic - not syncing: BUG!
> 
> The test calls vmap() directly, but vmap() is not supported on nommu
> systems, causing the crash.  TEST_IOV_ITER therefore needs to depend on
> MMU.

This is fixing mising assumption of a testing module.
The BUG is deserved AFAIU. The CVE should be reverted IMO.


Thanks,
Michal

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Re: CVE-2024-27406: lib/Kconfig.debug: TEST_IOV_ITER depends on MMU

[Greg Kroah-Hartman]

On Fri, May 17, 2024 at 07:42:14PM +0200, Michal Koutný wrote:
> On Fri, May 17, 2024 at 01:40:41PM GMT, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > BUG: failure at mm/nommu.c:318/vmap()!
> > Kernel panic - not syncing: BUG!
> > 
> > The test calls vmap() directly, but vmap() is not supported on nommu
> > systems, causing the crash.  TEST_IOV_ITER therefore needs to depend on
> > MMU.
> 
> This is fixing mising assumption of a testing module.
> The BUG is deserved AFAIU. The CVE should be reverted IMO.

Many people/distros run the built-in unit tests at boot time, and having
crashes is not a good idea.  So if you don't enable this option, great,
this CVE isn't relevent, but if you do, it's an in-kernel crash which is
not good, and this is the fix for that.

So I don't think this CVE should be rejected, sorry.

thanks,

greg k-h