[CVE-2026-46015][MODERATE 7.0] tcp: call sk_data_ready() after listener migration

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

CVE: CVE-2026-46015
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tcp: call sk_data_ready() after listener migration
Commit: ab5fdcd535645f6dbe6e9e21d96a08d141e88b4b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab5fdcd535645f6dbe6e9e21d96a08d141e88b4b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46015
Analysis date: Wed, 27 May 2026 16:42:34 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-46015 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46015

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 7.0
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-2026-46015	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'TCP listener migration in SO_REUSEPORT can add a child socket to the target accept queue without waking poll or blocking accept waiters, leaving server workers asleep. The same post migration path can dereference nsk after the migrated request has transferred the listener reference and another CPU may drop it, so the code needs RCU protection around sock_net(nsk) and sk_data_ready(). For the CVSS the PR:L is used because reliable triggering requires local control over a SO_REUSEPORT listener group or a cooperating service restart path, while remote clients can only assist by creating queued connections. The issue is not a pure remote packet parser bug. Impact is mainly denial of service, with paranoid memory lifetime concern due to possible stale listener dereference.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	REMOTE LOCK NETWORK HARDWARE KPANIC 	-	-	checked

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

ActionableScore=6
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged trigger: +1. Reliable triggering requires control over a `SO_REUSEPORT` listener group or a cooperating local service lifecycle such as listener shutdown or restart.
* Real lifetime corruption: +1. After `inet_csk_reqsk_queue_add()` succeeds, the listener reference can be transferred to `nreq->rsk_listener` and dropped by another CPU, making later `nsk` dereferences require RCU protection.
* Reliable DoS: +1. Missing `sk_data_ready()` can leave `poll()`, `epoll_wait()`, or blocking `accept()` waiters asleep indefinitely.
* Availability impact realistic: +1. The practical effect is service-level DoS from stuck accept waiters or unsafe listener dereference during migration.
* Common networking core path: +1. This is TCP listener and `SO_REUSEPORT` accept-queue migration logic.
* Hard race / special timing required: -1. The lifetime concern requires concurrent listener migration, accept, shutdown, or reference drop timing.
* Paranoid memory corruption / UAF concern: +2. The missing RCU read-side protection indicates a possible stale listener dereference after reference transfer, but no controlled UAF reclaim or LPE primitive is demonstrated.

3. Reachability analysis
Remote clients can help populate accept queues, but they cannot reliably trigger the bug alone. Practical triggering requires local or service-level control over a `SO_REUSEPORT` listener group and listener shutdown or migration timing. Containers may matter if an untrusted workload can run a TCP service with `SO_REUSEPORT` on the host kernel. The path is not a pure remote packet parser bug, but it is in common TCP infrastructure.

4. Severity interpretation
This is more than a simple missed wakeup because the patch also adds RCU protection for post-migration `nsk` dereferences. The realistic impact is DoS through stuck accept waiters or service disruption. The paranoid concern is stale listener dereference in TCP core, but the patch does not prove arbitrary write, controlled UAF reclaim, information disclosure, or privilege escalation.

5. One-sentence report phrase
TCP `SO_REUSEPORT` listener migration can miss wakeups for migrated accept-queue entries and may dereference a target listener after its reference is dropped, causing service DoS and a limited RCU lifetime concern.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This touches TCP core listener migration and includes an RCU lifetime issue, although current evidence supports DoS more strongly than practical privilege escalation.

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

Patch: tcp: call sk_data_ready() after listener migration
Commit: ab5fdcd535645f6dbe6e9e21d96a08d141e88b4b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab5fdcd535645f6dbe6e9e21d96a08d141e88b4b

Commit description:

When inet_csk_listen_stop() migrates an established child socket from
a closing listener to another socket in the same SO_REUSEPORT group,
the target listener gets a new accept-queue entry via
inet_csk_reqsk_queue_add(), but that path never notifies the target
listener's waiters. A nonblocking accept() still works because it
checks the queue directly, but poll()/epoll_wait() waiters and
blocking accept() callers can also remain asleep indefinitely.

Call READ_ONCE(nsk->sk_data_ready)(nsk) after a successful migration
in inet_csk_listen_stop().

However, after inet_csk_reqsk_queue_add() succeeds, the ref acquired
in reuseport_migrate_sock() is effectively transferred to
nreq->rsk_listener. Another CPU can then dequeue nreq via accept()
or listener shutdown, hit reqsk_put(), and drop that listener ref.
Since listeners are SOCK_RCU_FREE, wrap the post-queue_add()
dereferences of nsk in rcu_read_lock()/rcu_read_unlock(), which also
covers the existing sock_net(nsk) access in that path.

The reqsk_timer_handler() path does not need the same changes for two
reasons: half-open requests become readable only after the final ACK,
where tcp_child_process() already wakes the listener; and once nreq is
visible via inet_ehash_insert(), the success path no longer touches
nsk directly.

Fixes: 54b92e8 ("tcp: Migrate TCP_ESTABLISHED/TCP_SYN_RECV sockets in accept queues.")
Cc: stable@vger.kernel.org
Suggested-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Zhenzhong Wu <jt26wzz@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260422024554.130346-2-jt26wzz@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/inet_connection_sock.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=ab5fdcd535645f6dbe6e9e21d96a08d141e88b4b

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

The original Linux kernel CVE announcement for CVE-2026-46015 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46015

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  Paranoid ActionableScore: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).