# CVE-2022-49266: linux: In the Linux kernel, the following vulnerability has been resolved:  block: fix rq-qos breakage from skipping rq_qos_...

CVE-2022-49266 is fixed in linux on 1 platform, first by DEBIAN-CVE-2022-49266, released February 26, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2022-49266
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0028
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 26, 2025

## Description

In the Linux kernel, the following vulnerability has been resolved:  block: fix rq-qos breakage from skipping rq_qos_done_bio()  a647a524a467 ("block: don't call rq_qos_ops->done_bio if the bio isn't tracked") made bio_endio() skip rq_qos_done_bio() if BIO_TRACKED is not set. While this fixed a potential oops, it also broke blk-iocost by skipping the done_bio callback for merged bios.  Before, whether a bio goes through rq_qos_throttle() or rq_qos_merge(), rq_qos_done_bio() would be called on the bio on completion with BIO_TRACKED distinguishing the former from the latter. rq_qos_done_bio() is not called for bios which wenth through rq_qos_merge(). This royally confuses blk-iocost as the merged bios never finish and are considered perpetually in-flight.  One reliably reproducible failure mode is an intermediate cgroup geting stuck active preventing its children from being activated due to the leaf-only rule, leading to loss of control. The following is from resctl-bench protection scenario which emulates isolating a web server like workload from a memory bomb run on an iocost configuration which should yield a reasonable level of protection.    # cat /sys/block/nvme2n1/device/model   Samsung SSD 970 PRO 512GB   # cat /sys/fs/cgroup/io.cost.model   259:0 ctrl=user model=linear rbps=834913556 rseqiops=93622 rrandiops=102913 wbps=618985353 wseqiops=72325 wrandiops=71025   # cat /sys/fs/cgroup/io.cost.qos   259:0 enable=1 ctrl=user rpct=95.00 rlat=18776 wpct=95.00 wlat=8897 min=60.00 max=100.00   # resctl-bench -m 29.6G -r out.json run protection::scenario=mem-hog,loops=1   ...   Memory Hog Summary   ==================    IO Latency: R p50=242u:336u/2.5m p90=794u:1.4m/7.5m p99=2.7m:8.0m/62.5m max=8.0m:36.4m/350m               W p50=221u:323u/1.5m p90=709u:1.2m/5.5m p99=1.5m:2.5m/9.5m max=6.9m:35.9m/350m    Isolation and Request Latency Impact Distributions:                  min   p01   p05   p10   p25   p50   p75   p90   p95   p99   max  mean stdev   isol%       15.90 15.90 15.90 40.05 57.24 59.07 60.01 74.63 74.63 90.35 90.35 58.12 15.82   lat-imp%        0     0     0     0     0  4.55 14.68 15.54 233.5 548.1 548.1 53.88 143.6    Result: isol=58.12:15.82% lat_imp=53.88%:143.6 work_csv=100.0% missing=3.96%  The isolation result of 58.12% is close to what this device would show without any IO control.  Fix it by introducing a new flag BIO_QOS_MERGED to mark merged bios and calling rq_qos_done_bio() on them too. For consistency and clarity, rename BIO_TRACKED to BIO_QOS_THROTTLED. The flag checks are moved into rq_qos_done_bio() so that it's next to the code paths that set the flags.  With the patch applied, the above same benchmark shows:    # resctl-bench -m 29.6G -r out.json run protection::scenario=mem-hog,loops=1   ...   Memory Hog Summary   ==================    IO Latency: R p50=123u:84.4u/985u p90=322u:256u/2.5m p99=1.6m:1.4m/9.5m max=11.1m:36.0m/350m               W p50=429u:274u/995u p90=1.7m:1.3m/4.5m p99=3.4m:2.7m/11.5m max=7.9m:5.9m/26.5m    Isolation and Request Latency Impact Distributions:                  min   p01   p05   p10   p25   p50   p75   p90   p95   p99   max  mean stdev   isol%       84.91 84.91 89.51 90.73 92.31 94.49 96.36 98.04 98.71 100.0 100.0 94.42  2.81   lat-imp%        0     0     0     0     0  2.81  5.73 11.11 13.92 17.53 22.61  4.10  4.68    Result: isol=94.42:2.81% lat_imp=4.10%:4.68 work_csv=58.34% missing=0%

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.17.3-1 | [DEBIAN-CVE-2022-49266](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49266.md) | Feb 26, 2025 |
| Linux | linux Debian 13.5 (trixie) | 5.17.3-1 | [DEBIAN-CVE-2022-49266](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49266.md) | Feb 26, 2025 |
| Linux | linux Debian 14 | 5.17.3-1 | [DEBIAN-CVE-2022-49266](https://patchblox.com/security/data/fix/linux/debian-cve-2022-49266.md) | Feb 26, 2025 |

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