CVE-2023-53813 (GCVE-0-2023-53813)
Vulnerability from cvelistv5
Published
2025-12-09 00:01
Modified
2025-12-09 00:01
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: ext4: fix rbtree traversal bug in ext4_mb_use_preallocated During allocations, while looking for preallocations(PA) in the per inode rbtree, we can't do a direct traversal of the tree because ext4_mb_discard_group_preallocation() can paralelly mark the pa deleted and that can cause direct traversal to skip some entries. This was leading to a BUG_ON() being hit [1] when we missed a PA that could satisfy our request and ultimately tried to create a new PA that would overlap with the missed one. To makes sure we handle that case while still keeping the performance of the rbtree, we make use of the fact that the only pa that could possibly overlap the original goal start is the one that satisfies the below conditions: 1. It must have it's logical start immediately to the left of (ie less than) original logical start. 2. It must not be deleted To find this pa we use the following traversal method: 1. Descend into the rbtree normally to find the immediate neighboring PA. Here we keep descending irrespective of if the PA is deleted or if it overlaps with our request etc. The goal is to find an immediately adjacent PA. 2. If the found PA is on right of original goal, use rb_prev() to find the left adjacent PA. 3. Check if this PA is deleted and keep moving left with rb_prev() until a non deleted PA is found. 4. This is the PA we are looking for. Now we can check if it can satisfy the original request and proceed accordingly. This approach also takes care of having deleted PAs in the tree. (While we are at it, also fix a possible overflow bug in calculating the end of a PA) [1] https://lore.kernel.org/linux-ext4/CA+G9fYv2FRpLqBZf34ZinR8bU2_ZRAUOjKAD3+tKRFaEQHtt8Q@mail.gmail.com/
References
Impacted products
Vendor Product Version
Linux Linux Version: 3872778664e36528caf8b27f355e75482f6d562d
Version: 3872778664e36528caf8b27f355e75482f6d562d
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/mballoc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "339fee69a1daa71d6f97e47a867e2c32419a2406",
              "status": "affected",
              "version": "3872778664e36528caf8b27f355e75482f6d562d",
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              "versionType": "git"
            }
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        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ext4/mballoc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.4"
            },
            {
              "lessThan": "6.4",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.4.*",
              "status": "unaffected",
              "version": "6.4.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.5",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.4.8",
                  "versionStartIncluding": "6.4",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.5",
                  "versionStartIncluding": "6.4",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix rbtree traversal bug in ext4_mb_use_preallocated\n\nDuring allocations, while looking for preallocations(PA) in the per\ninode rbtree, we can\u0027t do a direct traversal of the tree because\next4_mb_discard_group_preallocation() can paralelly mark the pa deleted\nand that can cause direct traversal to skip some entries. This was\nleading to a BUG_ON() being hit [1] when we missed a PA that could satisfy\nour request and ultimately tried to create a new PA that would overlap\nwith the missed one.\n\nTo makes sure we handle that case while still keeping the performance of\nthe rbtree, we make use of the fact that the only pa that could possibly\noverlap the original goal start is the one that satisfies the below\nconditions:\n\n  1. It must have it\u0027s logical start immediately to the left of\n  (ie less than) original logical start.\n\n  2. It must not be deleted\n\nTo find this pa we use the following traversal method:\n\n1. Descend into the rbtree normally to find the immediate neighboring\nPA. Here we keep descending irrespective of if the PA is deleted or if\nit overlaps with our request etc. The goal is to find an immediately\nadjacent PA.\n\n2. If the found PA is on right of original goal, use rb_prev() to find\nthe left adjacent PA.\n\n3. Check if this PA is deleted and keep moving left with rb_prev() until\na non deleted PA is found.\n\n4. This is the PA we are looking for. Now we can check if it can satisfy\nthe original request and proceed accordingly.\n\nThis approach also takes care of having deleted PAs in the tree.\n\n(While we are at it, also fix a possible overflow bug in calculating the\nend of a PA)\n\n[1] https://lore.kernel.org/linux-ext4/CA+G9fYv2FRpLqBZf34ZinR8bU2_ZRAUOjKAD3+tKRFaEQHtt8Q@mail.gmail.com/"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-09T00:01:10.886Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/339fee69a1daa71d6f97e47a867e2c32419a2406"
        },
        {
          "url": "https://git.kernel.org/stable/c/9d3de7ee192a6a253f475197fe4d2e2af10a731f"
        }
      ],
      "title": "ext4: fix rbtree traversal bug in ext4_mb_use_preallocated",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2023-53813",
    "datePublished": "2025-12-09T00:01:10.886Z",
    "dateReserved": "2025-12-08T23:58:35.277Z",
    "dateUpdated": "2025-12-09T00:01:10.886Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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