CVE-2024-26737

Description

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->timer; timer->timer = NULL; spin_unlock(); hrtimer_cancel(&t->timer); kfree(t); /* UAF on t */ hrtimer_cancel(&t->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.

Gravité et risque d'exploitation

CVE-2024-26737 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.25 %, ce qui la place devant 15.8 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <addf5e297e6cbf5341f9c07720693ca9ba0057b5, <0281b919e175bb9c3128bd3872ac2903e9436e3f, 0, b00628b1c7d595ae5b544e059c27b1f5828314b4, 6.8, <=6.6.*, <5.15, <5268bb02107b9eedfdcd51db75b407d10043368c, <8327ed12e8ebc5436bfaa1786c49988894f9c8a6, 5.15, 6.7.7, 6.1.80, <=*, 6.6.19, <=5.15.*, <=6.7.*, <7d80a9e745fa5b47da3bca001f186c02485c7c33, 5.15.150) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c
• https://git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5
• https://git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6
• https://git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33
• https://git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f