Linux KernelOperating system · Linux
CVE-2021-46964
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn the Linux kernel, the following vulnerability has been resolved: scsi: qla2xxx: Reserve extra IRQ vectors Commit a6dcfe08487e ("scsi: qla2xxx: Limit interrupt vectors to number of CPUs") lowers the number of allocated MSI-X vectors to the number of CPUs. That breaks vector allocation assumptions in qla83xx_iospace_config(), qla24xx_enable_msix() and qla2x00_iospace_config(). Either of the functions computes maximum number of qpairs as: ha->max_qpairs = ha->msix_count - 1 (MB interrupt) - 1 (default response queue) - 1 (ATIO, in dual or pure target mode) max_qpairs is set to zero in case of two CPUs and initiator mode. The number is then used to allocate ha->queue_pair_map inside qla2x00_alloc_queues(). No allocation happens and ha->queue_pair_map is left NULL but the driver thinks there are queue pairs available. qla2xxx_queuecommand() tries to find a qpair in the map and crashes: if (ha->mqenable) { uint32_t tag; uint16_t hwq; struct qla_qpair *qpair = NULL; tag = blk_mq_unique_tag(cmd->request); hwq = blk_mq_unique_tag_to_hwq(tag); qpair = ha->queue_pair_map[hwq]; # <- HERE if (qpair) return qla2xxx_mqueuecommand(host, cmd, qpair); } BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 0 PID: 72 Comm: kworker/u4:3 Tainted: G W 5.10.0-rc1+ #25 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014 Workqueue: scsi_wq_7 fc_scsi_scan_rport [scsi_transport_fc] RIP: 0010:qla2xxx_queuecommand+0x16b/0x3f0 [qla2xxx] Call Trace: scsi_queue_rq+0x58c/0xa60 blk_mq_dispatch_rq_list+0x2b7/0x6f0 ? __sbitmap_get_word+0x2a/0x80 __blk_mq_sched_dispatch_requests+0xb8/0x170 blk_mq_sched_dispatch_requests+0x2b/0x50 __blk_mq_run_hw_queue+0x49/0xb0 __blk_mq_delay_run_hw_queue+0xfb/0x150 blk_mq_sched_insert_request+0xbe/0x110 blk_execute_rq+0x45/0x70 __scsi_execute+0x10e/0x250 scsi_probe_and_add_lun+0x228/0xda0 __scsi_scan_target+0xf4/0x620 ? __pm_runtime_resume+0x4f/0x70 scsi_scan_target+0x100/0x110 fc_scsi_scan_rport+0xa1/0xb0 [scsi_transport_fc] process_one_work+0x1ea/0x3b0 worker_thread+0x28/0x3b0 ? process_one_work+0x3b0/0x3b0 kthread+0x112/0x130 ? kthread_park+0x80/0x80 ret_from_fork+0x22/0x30 The driver should allocate enough vectors to provide every CPU it's own HW queue and still handle reserved (MB, RSP, ATIO) interrupts. The change fixes the crash on dual core VM and prevents unbalanced QP allocation where nr_hw_queues is two less than the number of CPUs.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisThe code follows a pointer that is null, crashing the process. An attacker who can reliably trigger it turns the crash into a denial of service. The fix is checking for null before use and handling the failure path gracefully.
General guidance for the null pointer dereference class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Linux KernelOperating system
>= 5.11, < 5.11.20>= 5.12, < 5.12.3CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped5.11.205.12.3
Linux Kernel 5.11.20+ or 5.12.3+
- Upgrade Linux kernel to version 5.11.20 or later for the 5.11 stable branch
- If using 5.12.x stable branch, upgrade to version 5.12.3 or later
- Reboot the system to load the updated kernel
- Verify the qla2xxx driver loads correctly: `modprobe qla2xxx` or check `lsmod | grep qla2xxx`
- Confirm no NULL pointer dereference errors in kernel logs: `dmesg | grep -i qla2xxx`
Generated from the published advisory — verify against the referenced sources before acting.
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Free · runs locallyCheck whether your project pulls in CVE-2021-46964 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-46964 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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