CVE-2024-41010

bpf: Fix too early release of tcx_entry

Published Jul 17, 2024 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix too early release of tcx_entry

Pedro Pinto and later independently also Hyunwoo Kim and Wongi Lee reported
an issue that the tcx_entry can be released too early leading to a use
after free (UAF) when an active old-style ingress or clsact qdisc with a
shared tc block is later replaced by another ingress or clsact instance.

Essentially, the sequence to trigger the UAF (one example) can be as follows:

1. A network namespace is created
2. An ingress qdisc is created. This allocates a tcx_entry, and
&tcx_entry->miniq is stored in the qdisc's miniqp->p_miniq. At the
same time, a tcf block with index 1 is created.
3. chain0 is attached to the tcf block. chain0 must be connected to
the block linked to the ingress qdisc to later reach the function
tcf_chain0_head_change_cb_del() which triggers the UAF.
4. Create and graft a clsact qdisc. This causes the ingress qdisc
created in step 1 to be removed, thus freeing the previously linked
tcx_entry:

rtnetlink_rcv_msg()
=> tc_modify_qdisc()
=> qdisc_create()
=> clsact_init() [a]
=> qdisc_graft()
=> qdisc_destroy()
=> __qdisc_destroy()
=> ingress_destroy() [b]
=> tcx_entry_free()
=> kfree_rcu() // tcx_entry freed

5. Finally, the network namespace is closed. This registers the
cleanup_net worker, and during the process of releasing the
remaining clsact qdisc, it accesses the tcx_entry that was
already freed in step 4, causing the UAF to occur:

cleanup_net()
=> ops_exit_list()
=> default_device_exit_batch()
=> unregister_netdevice_many()
=> unregister_netdevice_many_notify()
=> dev_shutdown()
=> qdisc_put()
=> clsact_destroy() [c]
=> tcf_block_put_ext()
=> tcf_chain0_head_change_cb_del()
=> tcf_chain_head_change_item()
=> clsact_chain_head_change()
=> mini_qdisc_pair_swap() // UAF

There are also other variants, the gist is to add an ingress (or clsact)
qdisc with a specific shared block, then to replace that qdisc, waiting
for the tcx_entry kfree_rcu() to be executed and subsequently accessing
the current active qdisc's miniq one way or another.

The correct fix is to turn the miniq_active boolean into a counter. What
can be observed, at step 2 above, the counter transitions from 0->1, at
step [a] from 1->2 (in order for the miniq object to remain active during
the replacement), then in [b] from 2->1 and finally [c] 1->0 with the
eventual release. The reference counter in general ranges from [0,2] and
it does not need to be atomic since all access to the counter is protected
by the rtnl mutex. With this in place, there is no longer a UAF happening
and the tcx_entry is freed at the correct time.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-7089-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-4 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-5 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-6 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7089-7 Linux kernel (Low Latency) vulnerabilities
Ubuntu USN Ubuntu USN USN-7090-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7095-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-7156-1 Linux kernel (GKE) vulnerabilities
History
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
Metrics epss

{'score': 0.00058}

epss

{'score': 0.00065}

Type Values Removed Values Added
First Time appeared Redhat
Redhat enterprise Linux
CPEs cpe:/a:redhat:enterprise_linux:9
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Aug 5, 2026, 11:34 AM
Reserved
Jul 12, 2024, 12:17 PM
Status
Modified
Published
Jul 17, 2024, 7:15 AM
Modified
Aug 4, 2026, 11:19 AM
Severity
Moderate
Public date
Jul 17, 2024, 12:00 AM