Subject: CVE-2024-39497: drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

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

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

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

drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

Lack of check for copy-on-write (COW) mapping in drm_gem_shmem_mmap
allows users to call mmap with PROT_WRITE and MAP_PRIVATE flag
causing a kernel panic due to BUG_ON in vmf_insert_pfn_prot:
BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));

Return -EINVAL early if COW mapping is detected.

This bug affects all drm drivers using default shmem helpers.
It can be reproduced by this simple example:
void *ptr = mmap(0, size, PROT_WRITE, MAP_PRIVATE, fd, mmap_offset);
ptr[0] = 0;

The Linux kernel CVE team has assigned CVE-2024-39497 to this issue.

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

	Issue introduced in 5.2 with commit 2194a63a818d and fixed in 5.15.169 with commit 3ae63a8c1685
	Issue introduced in 5.2 with commit 2194a63a818d and fixed in 6.1.114 with commit 2219e5f97244
	Issue introduced in 5.2 with commit 2194a63a818d and fixed in 6.6.35 with commit 1b4a8b89bf67
	Issue introduced in 5.2 with commit 2194a63a818d and fixed in 6.9.6 with commit 03c71c42809e
	Issue introduced in 5.2 with commit 2194a63a818d and fixed in 6.10 with commit 39bc27bd6880

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-2024-39497
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:
	drivers/gpu/drm/drm_gem_shmem_helper.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/3ae63a8c1685e16958560ec08d30defdc5b9cca0
	https://git.kernel.org/stable/c/2219e5f97244b79c276751a1167615b9714db1b0
	https://git.kernel.org/stable/c/1b4a8b89bf6787090b56424d269bf84ba00c3263
	https://git.kernel.org/stable/c/03c71c42809ef4b17f5d874cdb2d3bf40e847b86
	https://git.kernel.org/stable/c/39bc27bd688066a63e56f7f64ad34fae03fbe3b8