cifs: Fix server re-repick on subrequest retry

{
  "id": "56e76a18cbea5df8d55c74525f00c63266282165c30fac7ed5fb75d279f360f9",
  "url": "https://osv.dev/vulnerability/CVE-2024-42256",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "cifs: Fix server re-repick on subrequest retry",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: cifs: Fix server re-repick on subrequest retry When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server. If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting. Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry. The problem manifests as a warning looking something like: WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.",
    "evidence": "osv:CVE-2024-42256",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.10.1",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2024-42256",
      "aliases": [
        "CVE-2024-42256"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "3ee1a1fc39819906f04d6c62c180e760cd3a689d"
                },
                {
                  "fixed": "b1d0a566769b6fb3795b5289fc1daf9e0638d97a"
                },
                {
                  "fixed": "de40579b903883274fe203865f29d66b168b7236"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-42256.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.10.0"
                },
                {
                  "fixed": "6.10.1"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-42256.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:43.257230230Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/b1d0a566769b6fb3795b5289fc1daf9e0638d97a",
        "https://git.kernel.org/stable/c/de40579b903883274fe203865f29d66b168b7236",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/42xxx/CVE-2024-42256.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2024-42256",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/42xxx/CVE-2024-42256.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2024-42256",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 510733,
  "published_at": "2024-08-08T08:49:15.813+00:00"
}