CVE-2024-26737: bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel

First published: Wed Apr 03 2024(Updated: )

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.

Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67

Never miss a vulnerability like this again

Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.

Read MoreStart Free Trial

• agent/title
• agent/type
• collector/nvd-api
• source/NVD
• agent/remedy
• agent/first-publish-date
• collector/launchpad-cve
• source/Launchpad
• collector/nvd-cve
• agent/author
• agent/event
• collector/redhat-bugzilla
• source/Red Hat
• alias/CVE-2024-26737
• agent/software-canonical-lookup
• agent/severity
• agent/references
• agent/tags
• agent/description
• collector/mitre-cve
• source/MITRE
• agent/last-modified-date
• collector/security-tracker-debian
• source/Debian
• agent/softwarecombine
• collector/usn-cve
• source/Ubuntu
• package-manager/redhat
• package-manager/debian
• package-manager/ubuntu