| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-41045: bpf: Defer work in bpf_timer_cancel_and_free |
| |
| Description |
| =========== |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2024-41045 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.15 with commit b00628b1c7d595ae5b544e059c27b1f5828314b4 and fixed in 6.9.10 with commit 7aa5a19279c3639ae8b758b63f05d0c616a39fa1 |
| Issue introduced in 5.15 with commit b00628b1c7d595ae5b544e059c27b1f5828314b4 and fixed in 6.10 with commit a6fcd19d7eac1335eb76bc16b6a66b7f574d1d69 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-41045 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| kernel/bpf/helpers.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/7aa5a19279c3639ae8b758b63f05d0c616a39fa1 |
| https://git.kernel.org/stable/c/a6fcd19d7eac1335eb76bc16b6a66b7f574d1d69 |
