| 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-2021-46942: io_uring: fix shared sqpoll cancellation hangs |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| io_uring: fix shared sqpoll cancellation hangs |
| |
| [ 736.982891] INFO: task iou-sqp-4294:4295 blocked for more than 122 seconds. |
| [ 736.982897] Call Trace: |
| [ 736.982901] schedule+0x68/0xe0 |
| [ 736.982903] io_uring_cancel_sqpoll+0xdb/0x110 |
| [ 736.982908] io_sqpoll_cancel_cb+0x24/0x30 |
| [ 736.982911] io_run_task_work_head+0x28/0x50 |
| [ 736.982913] io_sq_thread+0x4e3/0x720 |
| |
| We call io_uring_cancel_sqpoll() one by one for each ctx either in |
| sq_thread() itself or via task works, and it's intended to cancel all |
| requests of a specified context. However the function uses per-task |
| counters to track the number of inflight requests, so it counts more |
| requests than available via currect io_uring ctx and goes to sleep for |
| them to appear (e.g. from IRQ), that will never happen. |
| |
| Cancel a bit more than before, i.e. all ctxs that share sqpoll |
| and continue to use shared counters. Don't forget that we should not |
| remove ctx from the list before running that task_work sqpoll-cancel, |
| otherwise the function wouldn't be able to find the context and will |
| hang. |
| |
| The Linux kernel CVE team has assigned CVE-2021-46942 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.12 with commit 37d1e2e3642e2380750d7f35279180826f29660e and fixed in 5.12.3 with commit cb5e0b3d0f993a6268c1a2c7ede2f9aa0c17ef68 |
| Issue introduced in 5.12 with commit 37d1e2e3642e2380750d7f35279180826f29660e and fixed in 5.13 with commit 734551df6f9bedfbefcd113ede665945e9de0b99 |
| |
| 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-2021-46942 |
| 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: |
| fs/io_uring.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/cb5e0b3d0f993a6268c1a2c7ede2f9aa0c17ef68 |
| https://git.kernel.org/stable/c/734551df6f9bedfbefcd113ede665945e9de0b99 |
