CVE-2026-74344: bpf: Clear rb node linkage when freeing bpf_rb_root

From: Greg Kroah-Hartman <[email protected]>

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

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

bpf: Clear rb node linkage when freeing bpf_rb_root

bpf_rb_root_free() detaches the root by copying the current rb_root_cached
and then replacing the live root with RB_ROOT_CACHED. It then walks the
copied root and drops each object contained in the tree.

This leaves the rb node state intact while dropping the object. If the
object is refcounted and survives the drop, its bpf_rb_node_kern still
contains an owner pointer to the freed root and stale rb tree linkage. If
a later bpf_rb_root allocation reuses the same address, bpf_rbtree_remove()
can incorrectly pass the owner check and call rb_erase_cached() on a node
whose rb pointers belong to the old tree.

Mirror the list draining behavior by marking nodes as busy while the root
is being detached, then clear the rb node and release the owner before
dropping the containing object. This makes surviving nodes unowned and
safe to reject from remove or accept for a later add.

The Linux kernel CVE team has assigned CVE-2026-74344 to this issue.


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

	Issue introduced in 6.3 with commit 9c395c1b99bd23f74bc628fa000480c49593d17f and fixed in 6.18.40 with commit 2eb39de4962f842d653e96818ae372665cd481fd
	Issue introduced in 6.3 with commit 9c395c1b99bd23f74bc628fa000480c49593d17f and fixed in 7.1.5 with commit 574612793bed416f6c05fe7c9b50e9eb0441997e
	Issue introduced in 6.3 with commit 9c395c1b99bd23f74bc628fa000480c49593d17f and fixed in 7.2-rc1 with commit 4a7910ee060d8ce55612f5b3cc267f3a265a3cec
	Issue introduced in 6.2.15 with commit 1d0675957d35ac5e514073481beda62e4e1e2ec5

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-2026-74344
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:
	kernel/bpf/helpers.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/2eb39de4962f842d653e96818ae372665cd481fd
	https://git.kernel.org/stable/c/574612793bed416f6c05fe7c9b50e9eb0441997e
	https://git.kernel.org/stable/c/4a7910ee060d8ce55612f5b3cc267f3a265a3cec