CVE-2026-43368: drm/i915: Fix potential overflow of shmem scatterlist length

CVE-2026-43368: drm/i915: Fix potential overflow of shmem scatterlist length

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

drm/i915: Fix potential overflow of shmem scatterlist length

When a scatterlists table of a GEM shmem object of size 4 GB or more is
populated with pages allocated from a folio, unsigned int .length
attribute of a scatterlist may get overflowed if total byte length of
pages allocated to that single scatterlist happens to reach or cross the
4GB limit.  As a consequence, users of the object may suffer from hitting
unexpected, premature end of the object's backing pages.

[278.780187] ------------[ cut here ]------------
[278.780377] WARNING: CPU: 1 PID: 2326 at drivers/gpu/drm/i915/i915_mm.c:55 remap_sg+0x199/0x1d0 [i915]
...
[278.780654] CPU: 1 UID: 0 PID: 2326 Comm: gem_mmap_offset Tainted: G S   U              6.17.0-rc1-CI_DRM_16981-ged823aaa0607+ #1 PREEMPT(voluntary)
[278.780656] Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER
[278.780658] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
[278.780659] RIP: 0010:remap_sg+0x199/0x1d0 [i915]
...
[278.780786] Call Trace:
[278.780787]  <TASK>
[278.780788]  ? __apply_to_page_range+0x3e6/0x910
[278.780795]  ? __pfx_remap_sg+0x10/0x10 [i915]
[278.780906]  apply_to_page_range+0x14/0x30
[278.780908]  remap_io_sg+0x14d/0x260 [i915]
[278.781013]  vm_fault_cpu+0xd2/0x330 [i915]
[278.781137]  __do_fault+0x3a/0x1b0
[278.781140]  do_fault+0x322/0x640
[278.781143]  __handle_mm_fault+0x938/0xfd0
[278.781150]  handle_mm_fault+0x12c/0x300
[278.781152]  ? lock_mm_and_find_vma+0x4b/0x760
[278.781155]  do_user_addr_fault+0x2d6/0x8e0
[278.781160]  exc_page_fault+0x96/0x2c0
[278.781165]  asm_exc_page_fault+0x27/0x30
...

That issue was apprehended by the author of a change that introduced it,
and potential risk even annotated with a comment, but then never addressed.

When adding folio pages to a scatterlist table, take care of byte length
of any single scatterlist not exceeding max_segment.

(cherry picked from commit 06249b4e691a75694c014a61708c007fb5755f60)

The Linux kernel CVE team has assigned CVE-2026-43368 to this issue.


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

	Issue introduced in 6.5 with commit 0b62af28f249b9c4036a05acfb053058dc02e2e2 and fixed in 6.6.130 with commit aeb7255531ba4a5c3a64938577170d08b78de399
	Issue introduced in 6.5 with commit 0b62af28f249b9c4036a05acfb053058dc02e2e2 and fixed in 6.12.78 with commit 1c956f0fccc26fefcbb507516c49d1db41c40471
	Issue introduced in 6.5 with commit 0b62af28f249b9c4036a05acfb053058dc02e2e2 and fixed in 6.18.19 with commit eae4bf4107571283031db96ce132e951615e2ae4
	Issue introduced in 6.5 with commit 0b62af28f249b9c4036a05acfb053058dc02e2e2 and fixed in 6.19.9 with commit 21a301f12d18797bf889c15497f922edfdaece3a
	Issue introduced in 6.5 with commit 0b62af28f249b9c4036a05acfb053058dc02e2e2 and fixed in 7.0 with commit 029ae067431ab9d0fca479bdabe780fa436706ea

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-2026-43368
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/i915/gem/i915_gem_shmem.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/aeb7255531ba4a5c3a64938577170d08b78de399
	https://git.kernel.org/stable/c/1c956f0fccc26fefcbb507516c49d1db41c40471
	https://git.kernel.org/stable/c/eae4bf4107571283031db96ce132e951615e2ae4
	https://git.kernel.org/stable/c/21a301f12d18797bf889c15497f922edfdaece3a
	https://git.kernel.org/stable/c/029ae067431ab9d0fca479bdabe780fa436706ea