CVE-2026-90002: ftrace: Take trace_array reference before accessing its ftrace_ops

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

ftrace: Take trace_array reference before accessing its ftrace_ops

The trace instance files set_ftrace_filter and set_ftrace_notrace was
updated to work with specific trace instances (trace_arrays). The issue is
that when these files are opened, there is a small race window where it
will use the ftrace_ops from the inode->private pointer to get a reference
to the trace_array and then take its reference. The problem is that the
ftrace_ops itself could be freed. If the rmdir on the instance happens at
the same time the set_ftrace_filter file is opened, the rmdir could have
also freed the ftrace_ops and referencing it will cause a use-after-free
bug and crash the kernel.

Instead, pass in the trace_array as the file private data (NULL for the
top level instance), and then pass both the trace_array and the ftrace_ops
to the ftrace_regex_open() function. If the trace_array is NULL, then it
just uses the ftrace_ops without the need to take its reference (like
normal). If the ftrace_ops is NULL, that is only the case for the top
level instance and the global_ops can be used.

This allows the trace_array to have its reference incremented before
touching the ftrace_ops that could also be freed when the instance is.

The Linux kernel CVE team has assigned CVE-2026-90002 to this issue.


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

	Issue introduced in 3.15 with commit 591dffdade9f07692a7dd3ed16830ec24e901ece and fixed in 6.18.52 with commit 83fd7eca5ab0d3ac3f23bff889175d847e21af06
	Issue introduced in 3.15 with commit 591dffdade9f07692a7dd3ed16830ec24e901ece and fixed in 7.2.5 with commit cee8f286794df916553d8d445eac5c323ec5b0f8
	Issue introduced in 3.15 with commit 591dffdade9f07692a7dd3ed16830ec24e901ece and fixed in 7.3-rc2 with commit 9100191e5acb2e5ea2313f436667bb5fce129f47

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-2026-90002
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:
	include/linux/ftrace.h
	kernel/trace/ftrace.c
	kernel/trace/trace.h
	kernel/trace/trace_functions.c
	kernel/trace/trace_stack.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/83fd7eca5ab0d3ac3f23bff889175d847e21af06
	https://git.kernel.org/stable/c/cee8f286794df916553d8d445eac5c323ec5b0f8
	https://git.kernel.org/stable/c/9100191e5acb2e5ea2313f436667bb5fce129f47