Subject: CVE-2024-49872: mm/gup: fix memfd_pin_folios alloc race panic

From: Greg Kroah-Hartman <[email-masked]>

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

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

mm/gup: fix memfd_pin_folios alloc race panic

If memfd_pin_folios tries to create a hugetlb page, but someone else
already did, then folio gets the value -EEXIST here:

        folio = memfd_alloc_folio(memfd, start_idx);
        if (IS_ERR(folio)) {
                ret = PTR_ERR(folio);
                if (ret != -EEXIST)
                        goto err;

then on the next trip through the "while start_idx" loop we panic here:

        if (folio) {
                folio_put(folio);

To fix, set the folio to NULL on error.

The Linux kernel CVE team has assigned CVE-2024-49872 to this issue.

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

	Issue introduced in 6.11 with commit 89c1905d9c14 and fixed in 6.11.3 with commit e28f39b359c0
	Issue introduced in 6.11 with commit 89c1905d9c14 and fixed in 6.12-rc1 with commit ce645b9fdc78

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-2024-49872
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:
	mm/gup.c

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/e28f39b359c0cfdcc011603e51187085a5f1e5e3
	https://git.kernel.org/stable/c/ce645b9fdc78ec5d28067286e92871ddae6817d5