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Race Condition Affecting kernel-livepatch-6.1.82-99.168 package, versions <0:1.0-0.amzn2023

Severity

 Recommended
high

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.05% (18th percentile)

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  • Snyk IDSNYK-AMZN2023-KERNELLIVEPATCH618299168-8495881
  • published11 Dec 2024
  • disclosed3 Apr 2024
Report a new vulnerability Found a mistake?

Introduced: 3 Apr 2024

CVE-2024-26737  (opens in a new tab)
CWE-362  (opens in a new tab)
CWE-416  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 kernel-livepatch-6.1.82-99.168 to version 0:1.0-0.amzn2023 or higher.
This issue was patched in ALAS2023-2024-784.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-livepatch-6.1.82-99.168 package and not the kernel-livepatch-6.1.82-99.168 package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

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

bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel

The following race is possible between bpf_timer_cancel_and_free and bpf_timer_cancel. It will lead a UAF on the timer->timer.

bpf_timer_cancel(); spin_lock(); t = timer->time; spin_unlock();

                bpf_timer_cancel_and_free();
                    spin_lock();
                    t = timer-&gt;timer;
                    timer-&gt;timer = NULL;
                    spin_unlock();
                    hrtimer_cancel(&amp;t-&gt;timer);
                    kfree(t);


/* UAF on t */
hrtimer_cancel(&amp;t-&gt;timer);

In bpf_timer_cancel_and_free, this patch frees the timer->timer after a rcu grace period. This requires a rcu_head addition to the "struct bpf_hrtimer". Another kfree(t) happens in bpf_timer_init, this does not need a kfree_rcu because it is still under the spin_lock and timer->timer has not been visible by others yet.

In bpf_timer_cancel, rcu_read_lock() is added because this helper can be used in a non rcu critical section context (e.g. from a sleepable bpf prog). Other timer->timer usages in helpers.c have been audited, bpf_timer_cancel() is the only place where timer->timer is used outside of the spin_lock.

Another solution considered is to mark a t->flag in bpf_timer_cancel and clear it after hrtimer_cancel() is done. In bpf_timer_cancel_and_free, it busy waits for the flag to be cleared before kfree(t). This patch goes with a straight forward solution and frees timer->timer after a rcu grace period.

CVSS Scores

version 3.1