CVE-2022-49075 (GCVE-0-2022-49075)
Vulnerability from cvelistv5
Published
2025-02-26 01:54
Modified
2026-08-05 08:53
Severity ?
8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix qgroup reserve overflow the qgroup limit We use extent_changeset->bytes_changed in qgroup_reserve_data() to record how many bytes we set for EXTENT_QGROUP_RESERVED state. Currently the bytes_changed is set as "unsigned int", and it will overflow if we try to fallocate a range larger than 4GiB. The result is we reserve less bytes and eventually break the qgroup limit. Unlike regular buffered/direct write, which we use one changeset for each ordered extent, which can never be larger than 256M. For fallocate, we use one changeset for the whole range, thus it no longer respects the 256M per extent limit, and caused the problem. The following example test script reproduces the problem: $ cat qgroup-overflow.sh #!/bin/bash DEV=/dev/sdj MNT=/mnt/sdj mkfs.btrfs -f $DEV mount $DEV $MNT # Set qgroup limit to 2GiB. btrfs quota enable $MNT btrfs qgroup limit 2G $MNT # Try to fallocate a 3GiB file. This should fail. echo echo "Try to fallocate a 3GiB file..." fallocate -l 3G $MNT/3G.file # Try to fallocate a 5GiB file. echo echo "Try to fallocate a 5GiB file..." fallocate -l 5G $MNT/5G.file # See we break the qgroup limit. echo sync btrfs qgroup show -r $MNT umount $MNT When running the test: $ ./qgroup-overflow.sh (...) Try to fallocate a 3GiB file... fallocate: fallocate failed: Disk quota exceeded Try to fallocate a 5GiB file... qgroupid         rfer         excl     max_rfer --------         ----         ----     -------- 0/5           5.00GiB      5.00GiB      2.00GiB Since we have no control of how bytes_changed is used, it's better to set it to u64.
References
Impacted products
Vendor Product Version
Linux Linux Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
Version: 7bc329c1836866ffac8b2613f780a51b3ffe786d
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{
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          "product": "Linux",
          "programFiles": [
            "fs/btrfs/extent_io.h"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.111",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.34",
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            },
            {
              "lessThanOrEqual": "5.16.*",
              "status": "unaffected",
              "version": "5.16.20",
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              "status": "unaffected",
              "version": "5.17.3",
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.18",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix qgroup reserve overflow the qgroup limit\n\nWe use extent_changeset-\u003ebytes_changed in qgroup_reserve_data() to record\nhow many bytes we set for EXTENT_QGROUP_RESERVED state. Currently the\nbytes_changed is set as \"unsigned int\", and it will overflow if we try to\nfallocate a range larger than 4GiB. The result is we reserve less bytes\nand eventually break the qgroup limit.\n\nUnlike regular buffered/direct write, which we use one changeset for\neach ordered extent, which can never be larger than 256M.  For\nfallocate, we use one changeset for the whole range, thus it no longer\nrespects the 256M per extent limit, and caused the problem.\n\nThe following example test script reproduces the problem:\n\n  $ cat qgroup-overflow.sh\n  #!/bin/bash\n\n  DEV=/dev/sdj\n  MNT=/mnt/sdj\n\n  mkfs.btrfs -f $DEV\n  mount $DEV $MNT\n\n  # Set qgroup limit to 2GiB.\n  btrfs quota enable $MNT\n  btrfs qgroup limit 2G $MNT\n\n  # Try to fallocate a 3GiB file. This should fail.\n  echo\n  echo \"Try to fallocate a 3GiB file...\"\n  fallocate -l 3G $MNT/3G.file\n\n  # Try to fallocate a 5GiB file.\n  echo\n  echo \"Try to fallocate a 5GiB file...\"\n  fallocate -l 5G $MNT/5G.file\n\n  # See we break the qgroup limit.\n  echo\n  sync\n  btrfs qgroup show -r $MNT\n\n  umount $MNT\n\nWhen running the test:\n\n  $ ./qgroup-overflow.sh\n  (...)\n\n  Try to fallocate a 3GiB file...\n  fallocate: fallocate failed: Disk quota exceeded\n\n  Try to fallocate a 5GiB file...\n\n  qgroupid\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 rfer\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 excl\u00a0\u00a0\u00a0\u00a0 max_rfer\n  --------\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ----\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ----\u00a0\u00a0\u00a0\u00a0 --------\n  0/5\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 5.00GiB\u00a0\u00a0\u00a0\u00a0\u00a0 5.00GiB\u00a0\u00a0\u00a0\u00a0\u00a0 2.00GiB\n\nSince we have no control of how bytes_changed is used, it\u0027s better to\nset it to u64."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable fallocate\u2192btrfs_qgroup_reserve_data path is invoked by in-kernel network servers: nfsd4_allocate (nfsd4_vfs_fallocate) and ksmbd vfs_fallocate on btrfs exports. Worst reasonable deployment is a multi-tenant NAS (e.g. Synology-style btrfs+qgroups over SMB/NFS) where a remote peer triggers the overflow with a \u003e4GiB allocate.\nAC:L - The attacker fully controls the trigger by issuing a single fallocate/ALLOCATE larger than 4GiB on a writable file; unsigned-int wrap of bytes_changed is deterministic, and qgroups are routinely enabled in the multi-tenant/NAS deployments where this limit matters.\nPR:L - Exploitation needs only an authenticated principal with write access (local unprivileged user, or NFS WR_STATE / SMB write after session setup). Enabling quotas requires CAP_SYS_ADMIN, but bypassing an already-enforced qgroup does not.\nUI:N - The attacker drives fallocate/ALLOCATE themselves against a file they can write; no separate victim action or privileged helper is required once the btrfs volume with qgroups is already serving.\nS:U - Impact stays within the host kernel\u2019s filesystem/quota authority for that volume; no VM escape, IOMMU bypass, or cross-sandbox boundary is crossed.\nC:N - The bug is pure qgroup accounting underflow from a 32-bit bytes_changed wrap; it discloses no kernel memory, file contents, or other tenants\u2019 data.\nI:H - The overflow causes qgroup_reserve() to reserve the wrapped (far smaller) amount, completely defeating the qgroup limit so the attacker can allocate and persist arbitrary extents beyond their authorized quota\u2014a complete loss of that isolation protection with attacker-controlled writes.\nA:H - Bypassing qgroup caps lets the attacker consume free space belonging to other tenants on the shared volume until ENOSPC, fully denying write service to co-tenants; free-path WARN_ON desync under panic_on_warn can also take the host down."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:53:44.398Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/0355387ea5b02d353c9415613fab908fac5c52a6"
        },
        {
          "url": "https://git.kernel.org/stable/c/f3d97b22a708bf9e3f3ac2ba232bcefd0b0c136b"
        },
        {
          "url": "https://git.kernel.org/stable/c/44277c50fdba5019ca25bfad1b71e2561b0de11b"
        },
        {
          "url": "https://git.kernel.org/stable/c/82ae73ac963cee877ce34f7c31b2b456b516e96c"
        },
        {
          "url": "https://git.kernel.org/stable/c/4b98799e181b4326a613108cf37acc1f55d21b45"
        },
        {
          "url": "https://git.kernel.org/stable/c/6bfff81286d4491f02dad7814bae5c77c9ad2320"
        },
        {
          "url": "https://git.kernel.org/stable/c/7941b74ed49b6db25efbef2256ebef843c11a010"
        },
        {
          "url": "https://git.kernel.org/stable/c/b642b52d0b50f4d398cb4293f64992d0eed2e2ce"
        }
      ],
      "title": "btrfs: fix qgroup reserve overflow the qgroup limit",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2022-49075",
    "datePublished": "2025-02-26T01:54:38.757Z",
    "dateReserved": "2025-02-26T01:49:39.245Z",
    "dateUpdated": "2026-08-05T08:53:44.398Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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