* [PATCH v2 2/3] Documentation: security-bugs: explain what is and is not a security bug
2026-05-03 11:35 [PATCH v2 0/3] Documentation: security-bugs: new updates covering triage and AI Willy Tarreau
2026-05-03 11:35 ` [PATCH v2 1/3] Documentation: security-bugs: do not systematically Cc the security team Willy Tarreau
@ 2026-05-03 11:35 ` Willy Tarreau
2026-05-05 14:10 ` Leon Romanovsky
2026-05-03 11:35 ` [PATCH v2 3/3] Documentation: security-bugs: clarify requirements for AI-assisted reports Willy Tarreau
2 siblings, 1 reply; 7+ messages in thread
From: Willy Tarreau @ 2026-05-03 11:35 UTC (permalink / raw)
To: greg
Cc: leon, security, Jonathan Corbet, skhan, workflows, linux-doc,
linux-kernel, Willy Tarreau, Greg KH
The use of automated tools to find bugs in random locations of the kernel
induces a raise of security reports even if most of them should just be
reported as regular bugs. This patch is an attempt at drawing a line
between what qualifies as a security bug and what does not, hoping to
improve the situation and ease decision on the reporter's side.
It defers the enumeration to a new file, threat-model.rst, that tries
to enumerate various classes of issues that are and are not security
bugs. This should permit to more easily update this file for various
subsystem-specific rules without having to revisit the security bug
reporting guide.
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Leon Romanovsky <leon@kernel.org>
Suggested-by: Leon Romanovsky <leon@kernel.org>
Suggested-by: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
Documentation/process/index.rst | 1 +
Documentation/process/security-bugs.rst | 28 +++
Documentation/process/threat-model.rst | 231 ++++++++++++++++++++++++
3 files changed, 260 insertions(+)
create mode 100644 Documentation/process/threat-model.rst
diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst
index dbd6ea16aca70..aa7c959a52b87 100644
--- a/Documentation/process/index.rst
+++ b/Documentation/process/index.rst
@@ -86,6 +86,7 @@ regressions and security problems.
debugging/index
handling-regressions
security-bugs
+ threat-model
cve
embargoed-hardware-issues
diff --git a/Documentation/process/security-bugs.rst b/Documentation/process/security-bugs.rst
index 6dc525858125e..3b44464dd9ba7 100644
--- a/Documentation/process/security-bugs.rst
+++ b/Documentation/process/security-bugs.rst
@@ -66,6 +66,34 @@ In addition, the following information are highly desirable:
the issue appear. It is useful to share them, as they can be helpful to
keep end users protected during the time it takes them to apply the fix.
+What qualifies as a security bug
+--------------------------------
+
+It is important that most bugs are handled publicly so as to involve the widest
+possible audience and find the best solution. By nature, bugs that are handled
+in closed discussions between a small set of participants are less likely to
+produce the best possible fix (e.g., risk of missing valid use cases, limited
+testing abilities).
+
+It turns out that the majority of the bugs reported via the security team are
+just regular bugs that have been improperly qualified as security bugs due to
+ignorance or misunderstanding of the Linux kernel's threat model described in
+Documentation/process/threat-model.rst, and ought to have been sent through
+the normal channels described in Documentation/admin-guide/reporting-issues.rst
+instead.
+
+The security list exists for urgent bugs that grant an attacker a capability
+they are not supposed to have on a correctly configured production system, and
+can be easily exploited, representing an imminent threat to many users. Before
+reporting, consider whether the issue actually crosses a trust boundary on such
+a system.
+
+If you are unsure whether an issue qualifies, err on the side of reporting
+privately: the security team would rather triage a borderline report than miss
+a real vulnerability. Reporting ordinary bugs to the security list, however,
+does not make them move faster and consumes triage capacity that other reports
+need.
+
Identifying contacts
--------------------
diff --git a/Documentation/process/threat-model.rst b/Documentation/process/threat-model.rst
new file mode 100644
index 0000000000000..8cd46483cd8b5
--- /dev/null
+++ b/Documentation/process/threat-model.rst
@@ -0,0 +1,231 @@
+.. _threatmodel:
+
+The Linux Kernel threat model
+=============================
+
+There are a lot of assumptions regarding what the kernel protects against and
+what it does not protect against. These assumptions tend to cause confusion for
+bug reports (:doc:`security-related ones <security-bugs>` vs
+:doc:`non-security ones <../admin-guide/reporting-issues>`), and can complicate
+security enforcement when the responsibilities for some boundaries is not clear
+between the kernel, distros, administrators and users.
+
+This document tries to clarify the responsibilities of the kernel in this
+domain.
+
+The kernel's responsibilities
+-----------------------------
+
+The kernel abstracts access to local hardware resources and to remote systems
+in a way that allows multiple local users to get a fair share of the available
+resources granted to them, and, when the underlying hardware permits, to assign
+a level of confidentiality to their communications and to the data they are
+processing or storing.
+
+The kernel assumes that the underlying hardware behaves according to its
+specifications. This includes the integrity of the CPU's instruction set, the
+transparency of the branch prediction unit and the cache units, the consistency
+of the Memory Management Unit (MMU), the isolation of DMA-capable peripherals
+(e.g., via IOMMU), state transitions in controllers, ranges of values read from
+registers, the respect of documented hardware limitations, etc.
+
+When hardware fails to maintain its specified isolation (e.g., CPU bugs,
+side-channels, hardware response to unexpected inputs), the kernel will usually
+attempt to implement reasonable mitigations. These are best-effort measures
+intended to reduce the attack surface or elevate the cost of an attack within
+the limits of the hardware's facilities; they do not constitute a
+kernel-provided safety guarantee.
+
+Users always perform their activities under the authority of an administrator
+who is able to grant or deny various types of permissions that may affect how
+users benefit from available resources, or the level of confidentiality of
+their activities. Administrators may also delegate all or part of their own
+permissions to some users, particularly via capabilities but not only. All this
+is performed via configuration (sysctl, file-system permissions etc).
+
+The Linux Kernel applies a certain collection of default settings that match
+its threat model. Distros have their own threat model and will come with their
+own configuration presets, that the administrator may have to adjust to better
+suit their expectations (relax or restrict).
+
+By default, the Linux Kernel guarantees the following protections when running
+on common processors featuring privilege levels and memory management units:
+
+* **User-based isolation**: an unprivileged user may restrict access to their
+ own data from other unprivileged users running on the same system. This
+ includes:
+
+ * stored data, via file system permissions
+ * in-memory data (pages are not accessible by default to other users)
+ * process activity (ptrace is not permitted to other users)
+ * inter-process communication (other users may not observe data exchanged via
+ UNIX domain sockets or other IPC mechanisms).
+ * network communications within the same or with other systems
+
+* **Capability-based protection**:
+
+ * users not having the ``CAP_SYS_ADMIN`` capability may not alter the
+ kernel's configuration, memory nor state, change other users' view of the
+ file system layout, grant any user capabilities they do not have, nor
+ affect the system's availability (shutdown, reboot, panic, hang, or making
+ the system unresponsive via unbounded resource exhaustion).
+ * users not having the ``CAP_NET_ADMIN`` capability may not alter the network
+ configuration, intercept nor spoof network communications from other users
+ nor systems.
+ * users not having ``CAP_SYS_PTRACE`` may not observe other users' processes
+ activities.
+
+When ``CONFIG_USER_NS`` is set, the kernel also permits unprivileged users to
+create their own user namespace in which they have all capabilities, but with a
+number of restrictions (they may not perform actions that have impacts on the
+initial user namespace, such as changing time, loading modules or mounting
+block devices). Please refer to ``user_namespaces(7)`` for more details, the
+possibilities of user namespaces are not covered in this document.
+
+The kernel also offers a lot of troubleshooting and debugging facilities, which
+can constitute attack vectors when placed in wrong hands. While some of them
+are designed to be accessible to regular local users with a low risk (e.g.
+kernel logs via ``/proc/kmsg``), some would expose enough information to
+represent a risk in most places and the decision to expose them is under the
+administrator's responsibility (perf events, traces), and others are not
+designed to be accessed by non-privileged users (e.g. debugfs). Access to these
+facilities by a user who has been explicitly granted permission by an
+administrator does not constitute a security breach.
+
+Bugs that permit to violate the principles above constitute security breaches.
+However, bugs that permit one violation only once another one was already
+achieved are only weaknesses. The kernel applies a number of self-protection
+measures whose purpose is to avoid crossing a security boundary when certain
+classes of bugs are found, but a failure of these extra protections do not
+constitute a vulnerability alone.
+
+What does not constitute a security bug
+---------------------------------------
+
+In the Linux kernel's threat model, the following classes of problems are
+**NOT** considered as Linux Kernel security bugs. However, when it is believed
+that the kernel could do better, they should be reported, so that they can be
+reviewed and fixed where reasonably possible, but they will be handled as any
+regular bug:
+
+* **Configuration**:
+
+ * outdated kernels and particularly end-of-life branches are out of the scope
+ of the kernel's threat model: administrators are responsible for keeping
+ their system up to date. For a bug to qualify as a security bug, it must be
+ demonstrated that it affects actively maintained versions.
+
+ * build-level: changes to the kernel configuration that are explicitly
+ documented as lowering the security level (e.g. ``CONFIG_NOMMU``), or
+ targeted at developers only.
+
+ * OS-level: changes to command line parameters, sysctls, filesystem
+ permissions, user capabilities, exposure of privileged interfaces, that
+ explicitly increase exposure by either offering non-default access to
+ unprivileged users, or reduce the kernel's ability to enforce some
+ protections or mitigations. Example: write access to procfs or debugfs.
+
+ * issues triggered only when using features intended for development or
+ debugging (e.g., lockdep, KASAN, fault-injection): these features are known
+ to introduce overhead and potential instability and are not intended for
+ production use.
+
+ * loading of explicitly insecure/broken/staging modules, and generally any
+ using any subsystem marked as experimental or not intended for production
+ use.
+
+ * running out-of-tree modules or unofficial kernel forks; these should be
+ reported to the relevant vendor.
+
+* **Excess of initial privileges**:
+
+ * actions performed by a user already possessing the privileges required to
+ perform that action or modify that state (e.g. ``CAP_SYS_ADMIN``,
+ ``CAP_NET_ADMIN``, ``CAP_SYS_RAWIO``, ``CAP_SYS_MODULE`` with no further
+ boundary being crossed).
+
+ * actions performed in user namespace without permitting anything in the
+ initial namespace that was not already permitted to the same user there.
+
+ * anything performed by the root user in the initial namespace (e.g. kernel
+ oops when writing to a privileged device).
+
+* **Out of production use**:
+
+ This covers theoretical/probabilistic attacks that rely on laboratory
+ conditions with zero system noise, or those requiring an unrealistic number
+ of attempts (e.g., billions of trials) that would be detected by standard
+ system monitoring long before success, such as:
+
+ * prediction of random numbers that only works in a totally silent
+ environment (such as IP ID, TCP ports or sequence numbers that can only be
+ guessed in a lab).
+
+ * activity observation and information leaks based on probabilistic
+ approaches that are prone to measurement noise and not realistically
+ reproducible on a production system.
+
+ * issues that can only be triggered by heavy attacks (e.g. brute force) whose
+ impact on the system makes it unlikely or impossible to remain undetected
+ before they succeed (e.g. consuming all memory before succeeding).
+
+ * problems seen only under development simulators, emulators, or combinations
+ that do not exist on real systems at the time of reporting (issues
+ involving tens of millions of threads, tens of thousands of CPUs,
+ unrealistic CPU frequencies, RAM sizes or disk capacities, network speeds.
+
+ * issues whose reproduction requires hardware modification or emulation,
+ including fake USB devices that pretend to be another one.
+
+ * as well as issues that can be triggered at a cost that is orders of
+ magnitude higher than the expected benefits (e.g. fully functional keyboard
+ emulator only to retrieve 7 uninitialized bytes in a structure, or
+ brute-force method involving millions of connection attempts to guess a
+ port number).
+
+* **Hardening failures**:
+
+ * ability to bypass some of the kernel's hardening measures with no
+ demonstrable exploit path (e.g. ASLR bypass, events timing or probing with
+ no demonstrable consequence). These are just weaknesses, not
+ vulnerabilities.
+
+ * missing argument checks and failure to report certain errors with no
+ immediate consequence.
+
+* **Random information leaks**:
+
+ This concerns information leaks of small data parts that happen to be there
+ and that cannot be chosen by the attacker, or face access restrictions:
+
+ * structure padding reported by syscalls or other interfaces.
+
+ * identifiers, partial data, non-terminated strings reported in error
+ messages.
+
+ * Leaks of kernel memory addresses/pointers do not constitute an immediately
+ exploitable vector and are not security bugs, though they must be reported
+ and fixed.
+
+* **Crafted file system images**:
+
+ * bugs triggered by mounting a corrupted or maliciously crafted file system
+ image are generally not security bugs, as the kernel assumes the underlying
+ storage media is under the administrator's control, unless the filesystem
+ driver is specifically documented as being hardened against untrusted media.
+
+ * issues that are resolved, mitigated, or detected by running a filesystem
+ consistency check (fsck) on the image prior to mounting.
+
+* **Physical access**:
+
+ Issues that require physical access to the machine, hardware modification, or
+ the use of specialized hardware (e.g., logic analyzers, DMA-attack tools over
+ PCI-E/Thunderbolt) are out of scope unless the system is explicitly
+ configured with technologies meant to defend against such attacks
+ (e.g. IOMMU).
+
+* **Functional and performance regressions**:
+
+ Any issue that can be mitigated by setting proper permissions and limits
+ doesn't qualify as a security bug.
--
2.52.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v2 3/3] Documentation: security-bugs: clarify requirements for AI-assisted reports
2026-05-03 11:35 [PATCH v2 0/3] Documentation: security-bugs: new updates covering triage and AI Willy Tarreau
2026-05-03 11:35 ` [PATCH v2 1/3] Documentation: security-bugs: do not systematically Cc the security team Willy Tarreau
2026-05-03 11:35 ` [PATCH v2 2/3] Documentation: security-bugs: explain what is and is not a security bug Willy Tarreau
@ 2026-05-03 11:35 ` Willy Tarreau
2026-05-05 14:09 ` Leon Romanovsky
2 siblings, 1 reply; 7+ messages in thread
From: Willy Tarreau @ 2026-05-03 11:35 UTC (permalink / raw)
To: greg
Cc: leon, security, Jonathan Corbet, skhan, workflows, linux-doc,
linux-kernel, Willy Tarreau, Greg KH
AI tools are increasingly used to assist in bug discovery. While these
tools can identify valid issues, reports that are submitted without
manual verification often lack context, contain speculative impact
assessments, or include unnecessary formatting. Such reports increase
triage effort, waste maintainers' time and may be ignored.
Reports where the reporter has verified the issue and the proposed fix
typically meet quality standards. This documentation outlines specific
requirements for length, formatting, and impact evaluation to reduce
the effort needed to deal with these reports.
Cc: Greg KH <gregkh@linuxfoundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
Documentation/process/security-bugs.rst | 55 +++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/Documentation/process/security-bugs.rst b/Documentation/process/security-bugs.rst
index 3b44464dd9ba7..bf62469a81266 100644
--- a/Documentation/process/security-bugs.rst
+++ b/Documentation/process/security-bugs.rst
@@ -159,6 +159,61 @@ the Linux kernel security team only. Your message will be triaged, and you
will receive instructions about whom to contact, if needed. Your message may
equally be forwarded as-is to the relevant maintainers.
+Responsible use of AI to find bugs
+----------------------------------
+
+A significant fraction of bug reports submitted to the security team are
+actually the result of code reviews assisted by AI tools. While this can be an
+efficient means to find bugs in rarely explored areas, it causes an overload on
+maintainers, who are sometimes forced to ignore such reports due to their poor
+quality or accuracy. As such, reporters must be particularly cautious about a
+number of points which tend to make these reports needlessly difficult to
+handle:
+
+ * **Length**: AI-generated reports tend to be excessively long, containing
+ multiple sections and excessive detail. This makes it difficult to spot
+ important information such as affected files, versions, and impact. Please
+ ensure that a clear summary of the problem and all critical details are
+ presented first. Do not require triage engineers to scan multiple pages of
+ text. Configure your tools to produce concise, human-style reports.
+
+ * **Formatting**: Most AI-generated reports are littered with Markdown tags.
+ These decorations complicate the search for important information and do
+ not survive the quoting processes involved in forwarding or replying.
+ Please **always convert your report to plain text** without any formatting
+ decorations before sending it.
+
+ * **Impact Evaluation**: Many AI-generated reports lack an understanding of
+ the kernel's threat model and go to great lengths inventing theoretical
+ consequences. This adds noise and complicates triage. Please stick to
+ verifiable facts (e.g., "this bug permits any user to gain CAP_NET_ADMIN")
+ without enumerating speculative implications. Have your tool read this
+ documentation as part of the evaluation process.
+
+ * **Reproducer**: AI-based tools are often capable of generating reproducers.
+ Please always ensure your tool provides one and **test it thoroughly**. If
+ the reproducer does not work, or if the tool cannot produce one, the
+ validity of the report should be seriously questioned.
+
+ * **Propose a Fix**: Many AI tools are actually better at writing code than
+ evaluating it. Please ask your tool to propose a fix and **test it** before
+ reporting the problem. If the fix cannot be tested because it relies on
+ rare hardware or almost extinct network protocols, the issue is likely not
+ a security bug. In any case, if a fix is proposed, it must adhere to
+ Documentation/process/submitting-patches.rst and include a 'Fixes:' tag
+ designating the commit that introduced the bug.
+
+Failure to consider these points exposes your report to the risk of being
+ignored.
+
+Use common sense when evaluating the report. If the affected file has not been
+touched for more than one year and is maintained by a single individual, it is
+likely that usage has declined and exposed users are virtually non-existent
+(e.g., drivers for very old hardware, obsolete filesystems). In such cases,
+there is no need to consume a maintainer's time with an unimportant report. If
+the issue is clearly trivial and publicly discoverable, you should report it
+directly to the public mailing lists.
+
Sending the report
------------------
--
2.52.0
^ permalink raw reply related [flat|nested] 7+ messages in thread