[CVE-2026-46312][MODERATE REGULAR] media: videobuf2: Set vma_flags in vb2_dma_sg_mmap

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-46312
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: media: videobuf2: Set vma_flags in vb2_dma_sg_mmap
Commit: feb17524aa4ec337749344be0db52b88663e25ab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=feb17524aa4ec337749344be0db52b88663e25ab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46312
Analysis date: Mon, 08 Jun 2026 14:17:18 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline Moderate. Manual review recommended only for panic_on_warn or exposed media DRM deployments
Manual review required: YES

Summary:
A local process with access to affected media or DRM device nodes can trigger a WARN during imported dma-buf mmap because vb2_dma_sg_mmap did not set VM_DONTEXPAND and VM_DONTDUMP, with practical impact limited to warning based disruption unless panic_on_warn turns it into a kernel crash.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-46312 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46312

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-46312	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-693;CWE-665;CWE-755;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'videobuf2 dma sg mappings did not set VM_DONTEXPAND and VM_DONTDUMP on the VMA, unlike the dma contig backend. A local process that can access the relevant media or DRM device can trigger mmap of an imported dma-buf and hit a WARN in drm_gem_mmap_obj. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to the affected device node, but not full administrator privileges. The issue is not network reachable and is triggered through local mmap behavior. Impact is mainly denial of service or warning based disruption. In a default system this is usually limited, but with panic_on_warn enabled the same WARN can become a kernel crash.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual review recommended only for panic_on_warn or exposed media DRM deployments (with actual score 2) 	MAYBE	READ DMAorINTERRUPT HARDWARE IPV6 MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate. Manual review recommended only for panic_on_warn or exposed media DRM deployments**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local UID 1000 process with access to the relevant media or DRM device can trigger the mmap path.
* No memory corruption: +0. The patch only sets missing VMA flags. There is no UAF, OOB write, double free, refcount corruption, or attacker controlled overwrite.
* No C or I impact: +0. No evidence of information disclosure or integrity modification.
* Availability impact is limited by default: +0. The demonstrated effect is a WARN and kernel taint, not a default kernel panic.

Paranoid signals:

* Local unprivileged trigger: +1. Device node access may be available to desktop users in video or render groups.
* Reliable kernel crash / strong DoS: +1. If panic_on_warn is enabled, the WARN in drm_gem_mmap_obj can become a kernel panic.
* Broad local desktop media or DRM relevance: +1. videobuf2, dma-buf, and DRM mmap paths are common on multimedia desktop systems, although the exact imported dma-buf path is configuration dependent.

Not counted:

* Remote reachable: +0. This is not network triggerable.
* Privilege escalation plausible: +0. No realistic LPE primitive is visible.
* Generic memory corruption: +0. Missing VM_DONTEXPAND and VM_DONTDUMP flags do not by themselves create a write or lifetime corruption primitive.
* Dirty Pipe like primitive: +0. There is no page cache or COW ownership bypass shown.

## 3. Reachability analysis

The trigger is local. A process must be able to use a media capture path and mmap an imported dma-buf through vb2_dma_sg_mmap and a DRM GEM shmem mmap path. This may be reachable by an ordinary desktop user if device permissions grant access to video or render nodes.

Namespaces and containers do not strongly lower the privilege requirement unless the relevant device nodes are passed into the container. If they are passed through, container users may be able to hit the same local device mmap path.

The path is not remotely reachable. It is also not a universal default path because it depends on media or camera drivers using videobuf2 dma sg and imported dma-buf mmap behavior. The provided report mentions an out of tree Apple ISP camera driver, but the commit notes that similar DRM GEM shmem users may also be affected.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local availability issue in default configurations. The realistic impact is a WARN and kernel taint during mmap.

The paranoid interpretation is a local DoS when panic_on_warn is enabled, because the same reachable WARN can become a host crash. There is no evidence of memory corruption, privilege escalation, sensitive data exposure, or cross-boundary policy bypass. Therefore it should not be treated as an Important-class kernel vulnerability based on the provided patch.

## 5. One-sentence report phrase

A local process with access to affected media or DRM device nodes can trigger a WARN during imported dma-buf mmap because vb2_dma_sg_mmap did not set VM_DONTEXPAND and VM_DONTDUMP, with practical impact limited to warning based disruption unless panic_on_warn turns it into a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended only to confirm whether panic_on_warn is enabled and whether affected media or DRM device nodes are exposed to untrusted users. If panic_on_warn is disabled and the relevant device path is not exposed, this can be treated as low-priority ordinary Moderate and is not an Important candidate.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: media: videobuf2: Set vma_flags in vb2_dma_sg_mmap
Commit: feb17524aa4ec337749344be0db52b88663e25ab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=feb17524aa4ec337749344be0db52b88663e25ab

Commit description:

vb2_dma_contig sets VMA flags VM_DONTEXPAND and VM_DONTDUMP and I do not
see a reason why vb2_dma_sg should behave differently. This avoids
hitting `WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));` in
drm_gem_mmap_obj() during mmap() of an imported dma-buf from the out of
tree Apple ISP camera capture driver which uses vb2_dma_sg_memops.

gst-launch-1.0 v4l2src ! gtk4paintablesink

[   38.201528] ------------[ cut here ]------------
[   38.202135] WARNING: CPU: 7 PID: 2362 at drivers/gpu/drm/drm_gem.c:1144 drm_gem_mmap_obj+0x1f8/0x210
[   38.203278] Modules linked in: rfcomm snd_seq_dummy snd_hrtimer
snd_seq snd_seq_device uinput nf_conntrack_netbios_ns
nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
nft_reject_inet nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables qrtr bnep
nls_ascii i2c_dev loop fuse dm_multipath nfnetlink brcmfmac_wcc
hid_magicmouse hci_bcm4377 brcmfmac brcmutil bluetooth ecdh_generic
cfg80211 ecc btrfs xor xor_neon rfkill hid_apple raid6_pq joydev
aop_als apple_nvmem_spmi industrialio snd_soc_aop apple_z2
snd_soc_cs42l84 tps6598x snd_soc_tas2764 macsmc_reboot spi_nor
macsmc_hwmon rtc_macsmc gpio_macsmc macsmc_power regmap_spmi
macsmc_input dockchannel_hid panel_summit appledrm nvme_apple dwc3
snd_soc_macaudio drm_client_lib nvme_core phy_apple_atc hwmon
apple_sart apple_dockchannel macsmc apple_rtkit_helper
spmi_apple_controller aop apple_wdt mfd_core nvmem_apple_efuses
pinctrl_apple_gpio apple_isp apple_dcp videobuf2_dma_sg mux_core
spi_apple
[   38.203300]  videobuf2_memops i2c_pasemi_platform snd_soc_apple_mca videobuf2_v4l2 videodev clk_apple_nco videobuf2_common snd_pcm_dmaengine adpdrm asahi apple_admac adpdrm_mipi drm_dma_helper pwm_apple i2c_pasemi_core drm_display_helper mc cec apple_dart ofpart apple_soc_cpufreq leds_pwm phram
[   38.217677] CPU: 7 UID: 1000 PID: 2362 Comm: gst-launch-1.0 Tainted: G        W           6.17.6+ #asahi-dev PREEMPT(full)
[   38.219040] Tainted: [W]=WARN
[   38.219398] Hardware name: Apple MacBook Pro (13-inch, M2, 2022) (DT)
[   38.220213] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[   38.221088] pc : drm_gem_mmap_obj+0x1f8/0x210
[   38.221643] lr : drm_gem_mmap_obj+0x78/0x210
[   38.222178] sp : ffffc0008dc678e0
[   38.222579] x29: ffffc0008dc678e0 x28: 0000000000042a97 x27: ffff8000b701b480
[   38.223465] x26: 00000000000000fb x25: ffffc0008dc67d20 x24: ffffc0008dc67968
[   38.224402] x23: ffff8000e3ca5600 x22: ffff8000265b7800 x21: ffff80003000c0c0
[   38.225279] x20: 0000000000000000 x19: ffff8000b68c5200 x18: ffffc0008dc67968
[   38.226151] x17: 0000000000000000 x16: 0000000000000000 x15: ffffc000810a30a8
[   38.227042] x14: 00007fff637effff x13: 00005555de91ffff x12: 00007fff63293fff
[   38.227942] x11: 0000000000000000 x10: ffff8000184ecf08 x9 : ffffc0007a1900c8
[   38.228824] x8 : ffffc0008dc67968 x7 : 0000000000000012 x6 : ffffc0015cf1c000
[   38.229703] x5 : ffffc0008dc676a0 x4 : ffffc00081a27dc0 x3 : 0000000000000038
[   38.230607] x2 : 0000000000000003 x1 : 0000000000000003 x0 : 00000000100000fb
[   38.231488] Call trace:
[   38.231806]  drm_gem_mmap_obj+0x1f8/0x210 (P)
[   38.232342]  drm_gem_mmap+0x140/0x260
[   38.232813]  __mmap_region+0x488/0x9a0
[   38.233277]  mmap_region+0xd0/0x148
[   38.233703]  do_mmap+0x350/0x5c0
[   38.234148]  vm_mmap_pgoff+0x14c/0x200
[   38.234612]  ksys_mmap_pgoff+0x150/0x208
[   38.235107]  __arm64_sys_mmap+0x34/0x50
[   38.235611]  invoke_syscall+0x50/0x120
[   38.236075]  el0_svc_common.constprop.0+0x48/0xf0
[   38.236680]  do_el0_svc+0x24/0x38
[   38.237113]  el0_svc+0x38/0x168
[   38.237507]  el0t_64_sync_handler+0xa0/0xe8
[   38.238034]  el0t_64_sync+0x198/0x1a0
[   38.238491] ---[ end trace 0000000000000000 ]---

There were discussions in [1] at the end of 2023 that mmap() on imported
dma-bufs should not be supported but as of v6.17 drm_gem_shmem_mmap() in
drm_gem_shmem_helper.c still supports it.
This might affect all gpu or accel drivers using drm_gem_shmem_mmap() or
the wrapper drm_gem_shmem_object_mmap().

[1] https://lore.kernel.org/dri-devel/bc7f7844-0aa3-4802-b203-69d58e8be2fa@linux.intel.com/

Cc: stable@vger.kernel.org
Fixes: 5ba3f75 ("[media] v4l: videobuf2: add DMA scatter/gather allocator")
Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/drm_gem.c
  drivers/media/common/videobuf2/videobuf2-dma-sg.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=feb17524aa4ec337749344be0db52b88663e25ab

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-46312 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46312

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 1
  Paranoid ActionableScore: 3

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).