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CVE-2023-54121

Estado: AplazadaAlta (7.8)—

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix incorrect splitting in btrfs_drop_extent_map_range

In production we were seeing a variety of WARN_ON()'s in the extent_map code, specifically in btrfs_drop_extent_map_range() when we have to call add_extent_mapping() for our second split.

Consider the following extent map layout

and then we call btrfs_drop_extent_map_range for [0, 36K), with skip_pinned == true. The initial loop will have

we will find the [0, 16k) extent, but since we are pinned we will skip it, which has this code

em_end here is 16K, so now the values are

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len should instead be 20K. This is a problem when we find the next extent at [32K, 48K), we need to split this extent to leave [36K, 48k), however the code for the split looks like this

In this case we have

and now we have an invalid extent_map in the tree that potentially overlaps other entries in the extent map. Even in the non-overlapping case we will have split->start set improperly, which will cause problems with any block related calculations.

We don't actually need len in this loop, we can simply use end as our end point, and only adjust start up when we find a pinned extent we need to skip.

Adjust the logic to do this, which keeps us from inserting an invalid extent map.

We only skip_pinned in the relocation case, so this is relatively rare, except in the case where you are running relocation a lot, which can happen with auto relocation on.

Detalles técnicos trazas, registros y código del informe original
	PINNED
	[0 16K)  [32K, 48K)

	start = 0
	end = 36K
	len = 36K

	start = em_end;
	if (end != (u64)-1)
		len = start + len - em_end;

	start = 16K
	len = 16K + 36K - 16K = 36K

	split->start = start + len;
	split->len = em_end - (start + len);

	em_end = 48K
	split->start = 16K + 36K       // this should be 16K + 20K
	split->len = 48K - (16K + 36K) // this overflows as 16K + 36K is 52K

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad local (AV:L/PR:L) sin interacción que corrompe estructuras del kernel btrfs, causando potencial DoS mediante mapas de extent inválidos y corrupción de datos de bloques.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Threat Intelligence ProgramRestrict File and Directory PermissionsRemote Data StorageFilter Network TrafficExecution PreventionEncrypt Sensitive Information

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2023-54121",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.8
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "55ef68990029fcd8d04d42fc184aa7fb18cf309e",
              "lessThan": "9f68e2105dd96cf0fafffffafb2337fbd0fbae1f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55ef68990029fcd8d04d42fc184aa7fb18cf309e",
              "lessThan": "b43a4c99d878cf5e59040e45c96bb0a8358bfb3b",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55ef68990029fcd8d04d42fc184aa7fb18cf309e",
              "lessThan": "c962098ca4af146f2625ed64399926a098752c9c",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "c87afd35a28b2661a2626a1b28e9fd69adcad9f9",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "2.6.32.19",
              "lessThan": "2.6.33",
              "versionType": "semver"
            }
          ],
          "programFiles": [
            "fs/btrfs/extent_map.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.33"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "2.6.33",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.1.47",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.4.12",
              "versionType": "semver",
              "lessThanOrEqual": "6.4.*"
            },
            {
              "status": "unaffected",
              "version": "6.5",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "fs/btrfs/extent_map.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2025-12-24T13:16:14.043",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/9f68e2105dd96cf0fafffffafb2337fbd0fbae1f",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/b43a4c99d878cf5e59040e45c96bb0a8358bfb3b",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/c962098ca4af146f2625ed64399926a098752c9c",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Deferred",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix incorrect splitting in btrfs_drop_extent_map_range\n\nIn production we were seeing a variety of WARN_ON()'s in the extent_map\ncode, specifically in btrfs_drop_extent_map_range() when we have to call\nadd_extent_mapping() for our second split.\n\nConsider the following extent map layout\n\n\tPINNED\n\t[0 16K)  [32K, 48K)\n\nand then we call btrfs_drop_extent_map_range for [0, 36K), with\nskip_pinned == true.  The initial loop will have\n\n\tstart = 0\n\tend = 36K\n\tlen = 36K\n\nwe will find the [0, 16k) extent, but since we are pinned we will skip\nit, which has this code\n\n\tstart = em_end;\n\tif (end != (u64)-1)\n\t\tlen = start + len - em_end;\n\nem_end here is 16K, so now the values are\n\n\tstart = 16K\n\tlen = 16K + 36K - 16K = 36K\n\nlen should instead be 20K.  This is a problem when we find the next\nextent at [32K, 48K), we need to split this extent to leave [36K, 48k),\nhowever the code for the split looks like this\n\n\tsplit->start = start + len;\n\tsplit->len = em_end - (start + len);\n\nIn this case we have\n\n\tem_end = 48K\n\tsplit->start = 16K + 36K       // this should be 16K + 20K\n\tsplit->len = 48K - (16K + 36K) // this overflows as 16K + 36K is 52K\n\nand now we have an invalid extent_map in the tree that potentially\noverlaps other entries in the extent map.  Even in the non-overlapping\ncase we will have split->start set improperly, which will cause problems\nwith any block related calculations.\n\nWe don't actually need len in this loop, we can simply use end as our\nend point, and only adjust start up when we find a pinned extent we need\nto skip.\n\nAdjust the logic to do this, which keeps us from inserting an invalid\nextent map.\n\nWe only skip_pinned in the relocation case, so this is relatively rare,\nexcept in the case where you are running relocation a lot, which can\nhappen with auto relocation on."
    }
  ],
  "lastModified": "2026-08-04T10:19:29.903",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}