CVE-2026-89546 (GCVE-0-2026-89546)
Vulnerability from cvelistv5
Published
2026-09-11 19:44
Modified
2026-10-19 08:48
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: close backchannel before destroying callback service A backchannel receive can complete a request while the NFS callback service is being torn down. xprt_complete_bc_request() removes the request from bc_pa_list, drops bc_alloc_count, marks the request in use, and then asks xprt_enqueue_bc_request() to hand it to the callback service. If teardown has already cleared xprt->bc_serv, xprt_enqueue_bc_request() currently returns without enqueueing or freeing the committed request. The xprt_get() taken on entry is leaked as well. If the producer wins the race before bc_serv is cleared, it can also enqueue onto sv_cb_list after nfs_callback_down() has stopped the callback threads, leaving the request linked to a svc_serv that is about to be freed. Close the producer side before callback threads are stopped. Add xprt_svc_shutdown_bc() to clear xprt->bc_serv under bc_pa_lock, and call it on callback shutdown and callback-start failure before stopping the service threads. Requests that lose the NULL transition in xprt_enqueue_bc_request() are released through the normal backchannel free path after balancing bc_slot_count. Finally, drain any remaining sv_cb_list requests after the callback threads have stopped and before svc_destroy() frees the service.
References
Impacted products
Vendor Product Version
Linux Linux Version: 441244d4273a8037b265fd254dfdaca5fa736ee2
Version: 441244d4273a8037b265fd254dfdaca5fa736ee2
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfs/callback.c",
            "include/linux/sunrpc/bc_xprt.h",
            "net/sunrpc/backchannel_rqst.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "6debde9e3e6ae21dcca75837b4247b13ca4ea2b8",
              "status": "affected",
              "version": "441244d4273a8037b265fd254dfdaca5fa736ee2",
              "versionType": "git"
            },
            {
              "lessThan": "3674f780f47d2906b5a0f7199b66973067bdfeca",
              "status": "affected",
              "version": "441244d4273a8037b265fd254dfdaca5fa736ee2",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfs/callback.c",
            "include/linux/sunrpc/bc_xprt.h",
            "net/sunrpc/backchannel_rqst.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: close backchannel before destroying callback service\n\nA backchannel receive can complete a request while the NFS callback\nservice is being torn down.  xprt_complete_bc_request() removes the\nrequest from bc_pa_list, drops bc_alloc_count, marks the request in use,\nand then asks xprt_enqueue_bc_request() to hand it to the callback\nservice.\n\nIf teardown has already cleared xprt-\u003ebc_serv, xprt_enqueue_bc_request()\ncurrently returns without enqueueing or freeing the committed request.\nThe xprt_get() taken on entry is leaked as well.  If the producer wins\nthe race before bc_serv is cleared, it can also enqueue onto sv_cb_list\nafter nfs_callback_down() has stopped the callback threads, leaving the\nrequest linked to a svc_serv that is about to be freed.\n\nClose the producer side before callback threads are stopped.  Add\nxprt_svc_shutdown_bc() to clear xprt-\u003ebc_serv under bc_pa_lock, and call\nit on callback shutdown and callback-start failure before stopping the\nservice threads.  Requests that lose the NULL transition in\nxprt_enqueue_bc_request() are released through the normal backchannel\nfree path after balancing bc_slot_count.  Finally, drain any remaining\nsv_cb_list requests after the callback threads have stopped and before\nsvc_destroy() frees the service."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The producer is xs_read_stream_call()/rpcrdma_bc_receive_call() handling RPC_CALL messages on the established NFSv4.1+ client TCP or RPC/RDMA transport; a malicious NFS server sends backchannel frames on that connection and reaches the bug without local access.\nAC:L - The attacker controls both sides of the race: they emit backchannel RPC_CALLs on the still-live xprt and force callback teardown via failed session setup, autofs expiry, or unmount, leaving rpc_rqst objects on sv_cb_list when svc_destroy() frees svc_serv.\nPR:N - A remote NFS peer needs no account or capability on the victim; backchannel RPC_CALLs are accepted on the connected NFSv4.1+ transport once a mount or mount attempt exists, with no local privileges at exploit time.\nUI:N - Boot-time, autofs, and Kubernetes NFSv4.1+ mounts are common; after that session exists the attacker drives backchannel traffic and callback teardown without further interactive victim action such as a manual mount.\nS:U - The use-after-free corrupts the in-kernel nfs_callback svc_serv and rpc_rqst objects on the client host and does not cross a VM, IOMMU, or other security-authority boundary.\nC:H - A raced enqueue leaves an in-use rpc_rqst linked into a freed svc_serv (sv_cb_list/sv_pools), and unlocked bc_serv readers can follow that dangling pointer, yielding a kernel-heap use-after-free read primitive.\nI:H - Use-after-free of svc_serv with queued rpc_rqst and svc_pool_wake_idle_thread on dying callback pools enables heap reuse of RPC service control structures, a standard kernel write and control-flow hijack primitive.\nA:H - svc_destroy() of a callback service that still has live backchannel requests, plus dereference of xprt-\u003ebc_serv after free, causes kernel oops or panic; the leak path also orphans rpc_rqst objects and xprt references."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:48:37.920Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/6debde9e3e6ae21dcca75837b4247b13ca4ea2b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/3674f780f47d2906b5a0f7199b66973067bdfeca"
        }
      ],
      "title": "SUNRPC: close backchannel before destroying callback service",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89546",
    "datePublished": "2026-09-11T19:44:21.898Z",
    "dateReserved": "2026-09-11T19:38:34.722Z",
    "dateUpdated": "2026-10-19T08:48:37.920Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.