CVE-2024-26737 Affecting kernel-debug-devel-matched package, versions <0:5.14.0-427.28.1.el9_4


Severity

Recommended
medium

Based on AlmaLinux security rating

    Threat Intelligence

    EPSS
    0.05% (17th percentile)

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  • Snyk ID SNYK-ALMALINUX9-KERNELDEBUGDEVELMATCHED-8327109
  • published 4 Nov 2024
  • disclosed 31 Jul 2024

How to fix?

Upgrade AlmaLinux:9 kernel-debug-devel-matched to version 0:5.14.0-427.28.1.el9_4 or higher.
This issue was patched in ALSA-2024:4928.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-debug-devel-matched package and not the kernel-debug-devel-matched package as distributed by AlmaLinux. See How to fix? for AlmaLinux:9 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
Expand this section

Red Hat

5.5 medium
  • Attack Vector (AV)
    Local
  • Attack Complexity (AC)
    Low
  • Privileges Required (PR)
    Low
  • User Interaction (UI)
    None
  • Scope (S)
    Unchanged
  • Confidentiality (C)
    None
  • Integrity (I)
    None
  • Availability (A)
    High
Expand this section

SUSE

6.4 medium