cve-2024-41045
Vulnerability from cvelistv5
Published
2024-07-29 14:32
Modified
2024-12-19 09:10
Severity ?
EPSS score ?
0.10% (0.25522)
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Defer work in bpf_timer_cancel_and_free Currently, the same case as previous patch (two timer callbacks trying to cancel each other) can be invoked through bpf_map_update_elem as well, or more precisely, freeing map elements containing timers. Since this relies on hrtimer_cancel as well, it is prone to the same deadlock situation as the previous patch. It would be sufficient to use hrtimer_try_to_cancel to fix this problem, as the timer cannot be enqueued after async_cancel_and_free. Once async_cancel_and_free has been done, the timer must be reinitialized before it can be armed again. The callback running in parallel trying to arm the timer will fail, and freeing bpf_hrtimer without waiting is sufficient (given kfree_rcu), and bpf_timer_cb will return HRTIMER_NORESTART, preventing the timer from being rearmed again. However, there exists a UAF scenario where the callback arms the timer before entering this function, such that if cancellation fails (due to timer callback invoking this routine, or the target timer callback running concurrently). In such a case, if the timer expiration is significantly far in the future, the RCU grace period expiration happening before it will free the bpf_hrtimer state and along with it the struct hrtimer, that is enqueued. Hence, it is clear cancellation needs to occur after async_cancel_and_free, and yet it cannot be done inline due to deadlock issues. We thus modify bpf_timer_cancel_and_free to defer work to the global workqueue, adding a work_struct alongside rcu_head (both used at _different_ points of time, so can share space). Update existing code comments to reflect the new state of affairs.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7aa5a19279c3639ae8b758b63f05d0c616a39fa1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a6fcd19d7eac1335eb76bc16b6a66b7f574d1d69
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/7aa5a19279c3639ae8b758b63f05d0c616a39fa1
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/a6fcd19d7eac1335eb76bc16b6a66b7f574d1d69
Impacted products
Vendor Product Version
Linux Linux Version: b00628b1c7d595ae5b544e059c27b1f5828314b4
Version: b00628b1c7d595ae5b544e059c27b1f5828314b4
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   Linux Linux Version: 5.15
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