CVE-2023-53178 (GCVE-0-2023-53178)
Vulnerability from cvelistv5
Published
2025-09-15 14:04
Modified
2025-09-16 08:02
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: fix zswap writeback race condition The zswap writeback mechanism can cause a race condition resulting in memory corruption, where a swapped out page gets swapped in with data that was written to a different page. The race unfolds like this: 1. a page with data A and swap offset X is stored in zswap 2. page A is removed off the LRU by zpool driver for writeback in zswap-shrink work, data for A is mapped by zpool driver 3. user space program faults and invalidates page entry A, offset X is considered free 4. kswapd stores page B at offset X in zswap (zswap could also be full, if so, page B would then be IOed to X, then skip step 5.) 5. entry A is replaced by B in tree->rbroot, this doesn't affect the local reference held by zswap-shrink work 6. zswap-shrink work writes back A at X, and frees zswap entry A 7. swapin of slot X brings A in memory instead of B The fix: Once the swap page cache has been allocated (case ZSWAP_SWAPCACHE_NEW), zswap-shrink work just checks that the local zswap_entry reference is still the same as the one in the tree. If it's not the same it means that it's either been invalidated or replaced, in both cases the writeback is aborted because the local entry contains stale data. Reproducer: I originally found this by running `stress` overnight to validate my work on the zswap writeback mechanism, it manifested after hours on my test machine. The key to make it happen is having zswap writebacks, so whatever setup pumps /sys/kernel/debug/zswap/written_back_pages should do the trick. In order to reproduce this faster on a vm, I setup a system with ~100M of available memory and a 500M swap file, then running `stress --vm 1 --vm-bytes 300000000 --vm-stride 4000` makes it happen in matter of tens of minutes. One can speed things up even more by swinging /sys/module/zswap/parameters/max_pool_percent up and down between, say, 20 and 1; this makes it reproduce in tens of seconds. It's crucial to set `--vm-stride` to something other than 4096 otherwise `stress` won't realize that memory has been corrupted because all pages would have the same data.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2b2811178e85553405b86e3fe78357b9b95889ce
Version: 2b2811178e85553405b86e3fe78357b9b95889ce
Version: 2b2811178e85553405b86e3fe78357b9b95889ce
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/zswap.c"
          ],
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              "version": "3.11"
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.4",
              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              ],
              "negate": false,
              "operator": "OR"
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          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: fix zswap writeback race condition\n\nThe zswap writeback mechanism can cause a race condition resulting in\nmemory corruption, where a swapped out page gets swapped in with data that\nwas written to a different page.\n\nThe race unfolds like this:\n1. a page with data A and swap offset X is stored in zswap\n2. page A is removed off the LRU by zpool driver for writeback in\n   zswap-shrink work, data for A is mapped by zpool driver\n3. user space program faults and invalidates page entry A, offset X is\n   considered free\n4. kswapd stores page B at offset X in zswap (zswap could also be\n   full, if so, page B would then be IOed to X, then skip step 5.)\n5. entry A is replaced by B in tree-\u003erbroot, this doesn\u0027t affect the\n   local reference held by zswap-shrink work\n6. zswap-shrink work writes back A at X, and frees zswap entry A\n7. swapin of slot X brings A in memory instead of B\n\nThe fix:\nOnce the swap page cache has been allocated (case ZSWAP_SWAPCACHE_NEW),\nzswap-shrink work just checks that the local zswap_entry reference is\nstill the same as the one in the tree.  If it\u0027s not the same it means that\nit\u0027s either been invalidated or replaced, in both cases the writeback is\naborted because the local entry contains stale data.\n\nReproducer:\nI originally found this by running `stress` overnight to validate my work\non the zswap writeback mechanism, it manifested after hours on my test\nmachine.  The key to make it happen is having zswap writebacks, so\nwhatever setup pumps /sys/kernel/debug/zswap/written_back_pages should do\nthe trick.\n\nIn order to reproduce this faster on a vm, I setup a system with ~100M of\navailable memory and a 500M swap file, then running `stress --vm 1\n--vm-bytes 300000000 --vm-stride 4000` makes it happen in matter of tens\nof minutes.  One can speed things up even more by swinging\n/sys/module/zswap/parameters/max_pool_percent up and down between, say, 20\nand 1; this makes it reproduce in tens of seconds.  It\u0027s crucial to set\n`--vm-stride` to something other than 4096 otherwise `stress` won\u0027t\nrealize that memory has been corrupted because all pages would have the\nsame data."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-09-16T08:02:20.669Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/2cab13f500a6333bd2b853783ac76be9e4956f8a"
        },
        {
          "url": "https://git.kernel.org/stable/c/ba700ea13bf0105a4773c654f7d3bef8adb64ab2"
        },
        {
          "url": "https://git.kernel.org/stable/c/04fc7816089c5a32c29a04ec94b998e219dfb946"
        }
      ],
      "title": "mm: fix zswap writeback race condition",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2023-53178",
    "datePublished": "2025-09-15T14:04:23.768Z",
    "dateReserved": "2025-09-15T13:59:19.065Z",
    "dateUpdated": "2025-09-16T08:02:20.669Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1"
}


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