CVE

CVE-2021-46942

Date: (C)2024-02-28   (M)2024-04-19

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.

CVSS Score and Metrics +CVSS Score and Metrics -

CVSS V3 Severity:		CVSS V2 Severity:
CVSS Score : 5.5		CVSS Score :
Exploit Score: 1.8		Exploit Score:
Impact Score: 3.6		Impact Score:
CVSS V3 Metrics:		CVSS V2 Metrics:
Attack Vector: LOCAL		Access Vector:
Attack Complexity: LOW		Access Complexity:
Privileges Required: LOW		Authentication:
User Interaction: NONE		Confidentiality:
Scope: UNCHANGED		Integrity:
Confidentiality: NONE		Availability:
Integrity: NONE
Availability: HIGH

Reference:

https://git.kernel.org/stable/c/734551df6f9bedfbefcd113ede665945e9de0b99

https://git.kernel.org/stable/c/cb5e0b3d0f993a6268c1a2c7ede2f9aa0c17ef68