CVE-2023-53021 net/sched: sch_taprio: fix possible use-after-free

What is CVE-2023-53021?

CVE-2023-53021 is a high-severity use after free vulnerability in Linux kernel, published on 27 Mar 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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

net/sched: sch_taprio: fix possible use-after-free

syzbot reported a nasty crash [1] in net_tx_action() which made little sense until we got a repro.

This repro installs a taprio qdisc, but providing an invalid TCA_RATE attribute.

qdisc_create() has to destroy the just initialized taprio qdisc, and taprio_destroy() is called.

However, the hrtimer used by taprio had already fired, therefore advance_sched() called __netif_schedule().

Then net_tx_action was trying to use a destroyed qdisc.

We can not undo the __netif_schedule(), so we must wait until one cpu serviced the qdisc before we can proceed.

Many thanks to Alexander Potapenko for his help.

[1] BUG: KMSAN: uninit-value in queued_spin_trylock include/asm-generic/qspinlock.h:94 [inline] BUG: KMSAN: uninit-value in do_raw_spin_trylock include/linux/spinlock.h:191 [inline] BUG: KMSAN: uninit-value in __raw_spin_trylock include/linux/spinlock_api_smp.h:89 [inline] BUG: KMSAN: uninit-value in _raw_spin_trylock+0x92/0xa0 kernel/locking/spinlock.c:138 queued_spin_trylock include/asm-generic/qspinlock.h:94 [inline] do_raw_spin_trylock include/linux/spinlock.h:191 [inline] __raw_spin_trylock include/linux/spinlock_api_smp.h:89 [inline] _raw_spin_trylock+0x92/0xa0 kernel/locking/spinlock.c:138 spin_trylock include/linux/spinlock.h:359 [inline] qdisc_run_begin include/net/sch_generic.h:187 [inline] qdisc_run+0xee/0x540 include/net/pkt_sched.h:125 net_tx_action+0x77c/0x9a0 net/core/dev.c:5086 __do_softirq+0x1cc/0x7fb kernel/softirq.c:571 run_ksoftirqd+0x2c/0x50 kernel/softirq.c:934 smpboot_thread_fn+0x554/0x9f0 kernel/smpboot.c:164 kthread+0x31b/0x430 kernel/kthread.c:376 ret_from_fork+0x1f/0x30

Uninit was created at: slab_post_alloc_hook mm/slab.h:732 [inline] slab_alloc_node mm/slub.c:3258 [inline] __kmalloc_node_track_caller+0x814/0x1250 mm/slub.c:4970 kmalloc_reserve net/core/skbuff.c:358 [inline] __alloc_skb+0x346/0xcf0 net/core/skbuff.c:430 alloc_skb include/linux/skbuff.h:1257 [inline] nlmsg_new include/net/netlink.h:953 [inline] netlink_ack+0x5f3/0x12b0 net/netlink/af_netlink.c:2436 netlink_rcv_skb+0x55d/0x6c0 net/netlink/af_netlink.c:2507 rtnetlink_rcv+0x30/0x40 net/core/rtnetlink.c:6108 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] netlink_unicast+0xf3b/0x1270 net/netlink/af_netlink.c:1345 netlink_sendmsg+0x1288/0x1440 net/netlink/af_netlink.c:1921 sock_sendmsg_nosec net/socket.c:714 [inline] sock_sendmsg net/socket.c:734 [inline] ____sys_sendmsg+0xabc/0xe90 net/socket.c:2482 ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2536 __sys_sendmsg net/socket.c:2565 [inline] __do_sys_sendmsg net/socket.c:2574 [inline] __se_sys_sendmsg net/socket.c:2572 [inline] __x64_sys_sendmsg+0x367/0x540 net/socket.c:2572 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

CPU: 0 PID: 13 Comm: ksoftirqd/0 Not tainted 6.0.0-rc2-syzkaller-47461-gac3859c02d7f #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022

Weakness: CWE-416

Which versions are affected by CVE-2023-53021?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2023-53021?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2023-53021 being exploited?

There is no known exploitation of CVE-2023-53021 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2023-53021, DEBIAN-CVE-2023-53021, GHSA-j94v-m9xh-gwvq, UBUNTU-CVE-2023-53021.