* [CVE-2026-90019][LOW] usb: gadget: fix null pointer dereference in usb_put_function_instance()
@ 2026-09-16 18:37 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-16 18:37 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90019
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: usb: gadget: fix null pointer dereference in usb_put_function_instance()
Commit: 0fc54a00954f9f4c3e3d4ffa64a530685d99a39b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fc54a00954f9f4c3e3d4ffa64a530685d99a39b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90019
Analysis date: Wed, 16 Sep 2026 14:37:50 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90019 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90019
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90019 LOW https://www.kernelcve.org/list/?q=CVE-2026-90019 CHECK WITH IMPACT FROM ORIG NN LOW 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-476;CWE-703;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the USB gadget function cleanup path occurs because usb_put_function_instance() can be called with fi allocated but fi fd not initialized. The UVC allocation error path can reach this state before try_get_usb_function_instance() assigns the function driver pointer, causing a kernel crash when the cleanup helper reads fi fd mod. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate USB gadget or configfs control to a reduced capability service account or container root, while the normal base case is PR:H for administrator controlled gadget setup. The issue is not network reachable and requires local access to the USB gadget configuration interface. Impact is denial of service via kernel crash only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DANGER NULLPTR USB SIMPLEFIX ERRORPATH IMPROVEONLY LINUS SYZBOT INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0. Arithmetic was +1 reliable kernel crash and -2 proven host-admin-equivalent gadget/configfs control, clamped at 0.
* Conservative score: 0.
* Raw paranoid score: 0. No additional paranoid point is supported because the bug is a NULL dereference only, not UAF, refcount corruption, OOB, or authorization bypass.
* Paranoid score: 0.
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changed the score.
2. Signal breakdown
Positive signals:
* +1 Reliable kernel crash / strong DoS. The commit states that dereferencing `fi->fd->mod` when `fi->fd` is NULL can crash the kernel in the UVC allocation error path.
Negative signals:
* -2 Host-admin-equivalent privilege required. USB gadget function instance creation and configfs gadget configuration are normally administrator-controlled host operations.
Material non-awarded signals:
* Real UAF not awarded. The object is allocated but one member pointer is NULL, not freed and reused.
* Concrete repeated release/refcount not awarded. There is no first put/free that may end lifetime followed by a second lifetime mutation on the same dangling reference.
* Structured stale-object leverage not awarded. The stale-use model is not present.
* Weak LPE and Strong LPE not awarded. No controlled reclaim, arbitrary write, callback control, refcount takeover, or privilege boundary primitive is established.
* C/I not awarded. The demonstrated primitive is a NULL pointer dereference leading to crash only.
* Extra Availability not awarded. The only availability effect is the same kernel crash already counted.
* Remote reachability not awarded. This is local USB gadget configuration/control path behavior, not packet-triggered or network-reachable behavior.
Repeated-release/refcount checklist:
* First release can end lifetime: no evidence.
* Exact same reference survives after first release: not applicable.
* Second operation mutates lifetime/refcount: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The trigger is through USB gadget function instance handling, specifically an error path in UVC function allocation before `try_get_usb_function_instance()` has assigned `fi->fd`. A caller that can configure/create the relevant USB gadget function can reach the cleanup path where `usb_put_function_instance()` is called.
The complete practical trigger is host-local and normally requires administrator-level access to USB gadget configfs controls. No evidence shows that an ordinary unprivileged user can create the needed gadget function instance. No evidence shows namespace-scoped reachability for the complete operation. No network trigger is established. No race is required. No special rare hardware prerequisite is needed beyond a system using USB gadget functionality, but the control interface remains privileged.
4. Primitive and severity interpretation
The exact primitive is a NULL pointer dereference of `fi->fd` inside `usb_put_function_instance()`. This is an invalid-state cleanup bug, not a lifetime-after-free bug. The object `fi` exists, but its `fd` field is not initialized yet in the UVC allocation error path.
This is Class C because the demonstrated behavior is crash/DoS through invalid dereference without an independently useful corruption primitive. It is cleanup-path behavior and does not show broader active structured reuse. There is no concrete repeated lifetime/refcount mutation. The first lifetime operation does not free the object and leave the same reference for a second release. The second operation is just a read through a NULL member pointer.
Demonstrated consequence is local kernel crash/DoS. Speculative privilege escalation is not supported by the patch mechanics. ImportantCandidate is NO because no Class A or meaningful unresolved Class B primitive exists. AutoDowngradeAllowed is YES because this is a constrained host-admin-gated NULL dereference with crash-only impact.
Likely operational severity: ordinary Moderate or Low-like triage item, not Important-class.
5. One-sentence report phrase
A NULL pointer dereference in `usb_put_function_instance()` can crash the kernel when the UVC gadget allocation error path calls the cleanup helper before `fi->fd` is initialized.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: the patch establishes a straightforward NULL pointer dereference in a privileged local USB gadget/configfs error path, with no UAF, refcount mutation, memory corruption, authorization bypass, or network exposure.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: gadget: fix null pointer dereference in usb_put_function_instance()
Commit: 0fc54a00954f9f4c3e3d4ffa64a530685d99a39b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fc54a00954f9f4c3e3d4ffa64a530685d99a39b
Commit description:
usb_put_function_instance() attempts to dereference fd inside fi struct
to get mod in uvc_alloc_inst() error path. However, fd is not allocated
until later in try_get_usb_function_instance() after allocating fi in
uvc_alloc_inst() and thus guranteed to be null in error path. Fix this
by adding a null check for fi->fd that returns if fd is null.
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=fd6ef980cf1c722be639
Fixes: 0062f6e ("usb: gadget: add a forward pointer from usb_function to its "instance"")
Cc: stable <[email protected]>
Signed-off-by: Jeffin Philip <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/usb/gadget/functions.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=0fc54a00954f9f4c3e3d4ffa64a530685d99a39b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90019 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90019
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:H/UI:N/S:U/C:N/I:N/A:H
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: unknown
Paranoid ActionableScore: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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