CVE-2023-54121 (GCVE-0-2023-54121)

Vulnerability from cvelistv5 – Published: 2025-12-24 13:06 – Updated: 2025-12-24 13:06
VLAI?
Title
btrfs: fix incorrect splitting in btrfs_drop_extent_map_range
Summary
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 PINNED [0 16K) [32K, 48K) and then we call btrfs_drop_extent_map_range for [0, 36K), with skip_pinned == true. The initial loop will have start = 0 end = 36K len = 36K we will find the [0, 16k) extent, but since we are pinned we will skip it, which has this code start = em_end; if (end != (u64)-1) len = start + len - em_end; em_end here is 16K, so now the values are start = 16K len = 16K + 36K - 16K = 36K 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 split->start = start + len; split->len = em_end - (start + len); In this case we have em_end = 48K split->start = 16K + 36K // this should be 16K + 20K split->len = 48K - (16K + 36K) // this overflows as 16K + 36K is 52K 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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 55ef68990029fcd8d04d42fc184aa7fb18cf309e , < 9f68e2105dd96cf0fafffffafb2337fbd0fbae1f (git)
Affected: 55ef68990029fcd8d04d42fc184aa7fb18cf309e , < b43a4c99d878cf5e59040e45c96bb0a8358bfb3b (git)
Affected: 55ef68990029fcd8d04d42fc184aa7fb18cf309e , < c962098ca4af146f2625ed64399926a098752c9c (git)
Affected: c87afd35a28b2661a2626a1b28e9fd69adcad9f9 (git)
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    Linux Linux Affected: 2.6.33
Unaffected: 0 , < 2.6.33 (semver)
Unaffected: 6.1.47 , ≤ 6.1.* (semver)
Unaffected: 6.4.12 , ≤ 6.4.* (semver)
Unaffected: 6.5 , ≤ * (original_commit_for_fix)
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/extent_map.c"
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          "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()\u0027s 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-\u003estart = start + len;\n\tsplit-\u003elen = em_end - (start + len);\n\nIn this case we have\n\n\tem_end = 48K\n\tsplit-\u003estart = 16K + 36K       // this should be 16K + 20K\n\tsplit-\u003elen = 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-\u003estart set improperly, which will cause problems\nwith any block related calculations.\n\nWe don\u0027t 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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-24T13:06:41.185Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/9f68e2105dd96cf0fafffffafb2337fbd0fbae1f"
        },
        {
          "url": "https://git.kernel.org/stable/c/b43a4c99d878cf5e59040e45c96bb0a8358bfb3b"
        },
        {
          "url": "https://git.kernel.org/stable/c/c962098ca4af146f2625ed64399926a098752c9c"
        }
      ],
      "title": "btrfs: fix incorrect splitting in btrfs_drop_extent_map_range",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2023-54121",
    "datePublished": "2025-12-24T13:06:41.185Z",
    "dateReserved": "2025-12-24T13:02:52.520Z",
    "dateUpdated": "2025-12-24T13:06:41.185Z",
    "state": "PUBLISHED"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2023-54121\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-12-24T13:16:14.043\",\"lastModified\":\"2025-12-24T13:16:14.043\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"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()\u0027s 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-\u003estart = start + len;\\n\\tsplit-\u003elen = em_end - (start + len);\\n\\nIn this case we have\\n\\n\\tem_end = 48K\\n\\tsplit-\u003estart = 16K + 36K       // this should be 16K + 20K\\n\\tsplit-\u003elen = 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-\u003estart set improperly, which will cause problems\\nwith any block related calculations.\\n\\nWe don\u0027t 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.\"}],\"metrics\":{},\"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\"}]}}"
  }
}


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