{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  null_blk: reject per-device queue resize for shared tag set  When shared_tags is enabled, null_setup_tagset() makes the device use the global tag_set, whose driver_data stays NULL. null_map_queues() therefore falls back to the module-wide g_submit_queues/g_poll_queues instead of any per-device value.  Resizing submit_queues or poll_queues via configfs on such a device calls blk_mq_update_nr_hw_queues() on the shared set, shrinking set-\u003enr_hw_queues.  __blk_mq_realloc_hw_ctxs() only grows the q-\u003equeue_hw_ctx[] allocation, so on shrink it merely exits and NULLs the now-excess hctx slots. null_map_queues(), however, keeps mapping CPUs with the unchanged g_submit_queues/g_poll_queues, so mq_map[] ends up pointing at those NULLed hctx slots. blk_mq_map_swqueue() then dereferences the NULL hctx (hctx-\u003ecpumask), crashing the kernel:  [  460.218374] KASAN: null-ptr-deref in range [0x0000000000000098-0x000000000000009f] [  460.219003] CPU: 24 UID: 0 PID: 1492 Comm: sh Not tainted 7.2.0-rc2+ #67 PREEMPT(full) [  460.219792] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 [  460.220452] RIP: 0010:blk_mq_map_swqueue+0x4db/0x1430 ...... [  460.228977] Call Trace: [  460.229175]  \u003cTASK\u003e [  460.229354]  blk_mq_update_nr_hw_queues+0xd49/0x11c0 [  460.229779]  ? __pfx_blk_mq_update_nr_hw_queues+0x10/0x10 [  460.230200]  nullb_update_nr_hw_queues+0x1a9/0x370 [null_blk] [  460.230694]  nullb_device_submit_queues_store+0xd9/0x170 [null_blk] [  460.231190]  ? __pfx_nullb_device_submit_queues_store+0x10/0x10 [null_blk] [  460.231776]  ? configfs_write_iter+0x35c/0x4e0 [  460.232122]  configfs_write_iter+0x286/0x4e0 [  460.232460]  vfs_write+0x52d/0xd00 [  460.232779]  ? __x64_sys_openat+0x108/0x1d0 [  460.233106]  ? __pfx_vfs_write+0x10/0x10 [  460.233413]  ? fdget_pos+0x1cf/0x4c0 [  460.233745]  ? fput_close+0x133/0x190 [  460.234038]  ? __pfx_expand_files+0x10/0x10 [  460.234368]  ksys_write+0xfc/0x1d0  Reproducer: modprobe null_blk shared_tags=1 submit_queues=64 poll_queues=1 mkdir /sys/kernel/config/nullb/dev echo 1 \u003e /sys/kernel/config/nullb/dev/power echo 1 \u003e /sys/kernel/config/nullb/dev/submit_queues  A per-device resize of a shared tag set is meaningless anyway, so reject it with -EINVAL in nullb_update_nr_hw_queues() when the device is bound to the global tag_set.",
  "id": "DEBIAN-CVE-2026-90186",
  "modified": "2026-09-18T04:47:37.743627315Z",
  "published": "2026-09-17T17:17:13.127Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-90186"
    }
  ],
  "upstream": [
    "CVE-2026-90186"
  ]
}