GHSA-5C3M-P5M6-P659

Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-05-06 21:31
VLAI?
Details

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

f2fs: fix use-after-free of sbi in f2fs_compress_write_end_io()

In f2fs_compress_write_end_io(), dec_page_count(sbi, type) can bring the F2FS_WB_CP_DATA counter to zero, unblocking f2fs_wait_on_all_pages() in f2fs_put_super() on a concurrent unmount CPU. The unmount path then proceeds to call f2fs_destroy_page_array_cache(sbi), which destroys sbi->page_array_slab via kmem_cache_destroy(), and eventually kfree(sbi). Meanwhile, the bio completion callback is still executing: when it reaches page_array_free(sbi, ...), it dereferences sbi->page_array_slab — a destroyed slab cache — to call kmem_cache_free(), causing a use-after-free.

This is the same class of bug as CVE-2026-23234 (which fixed the equivalent race in f2fs_write_end_io() in data.c), but in the compressed writeback completion path that was not covered by that fix.

Fix this by moving dec_page_count() to after page_array_free(), so that all sbi accesses complete before the counter decrement that can unblock unmount. For non-last folios (where atomic_dec_return on cic->pending_pages is nonzero), dec_page_count is called immediately before returning — page_array_free is not reached on this path, so there is no post-decrement sbi access. For the last folio, page_array_free runs while the F2FS_WB_CP_DATA counter is still nonzero (this folio has not yet decremented it), keeping sbi alive, and dec_page_count runs as the final operation.

Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-31702"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-01T14:16:20Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nf2fs: fix use-after-free of sbi in f2fs_compress_write_end_io()\n\nIn f2fs_compress_write_end_io(), dec_page_count(sbi, type) can bring\nthe F2FS_WB_CP_DATA counter to zero, unblocking\nf2fs_wait_on_all_pages() in f2fs_put_super() on a concurrent unmount\nCPU. The unmount path then proceeds to call\nf2fs_destroy_page_array_cache(sbi), which destroys\nsbi-\u003epage_array_slab via kmem_cache_destroy(), and eventually\nkfree(sbi). Meanwhile, the bio completion callback is still executing:\nwhen it reaches page_array_free(sbi, ...), it dereferences\nsbi-\u003epage_array_slab \u2014 a destroyed slab cache \u2014 to call\nkmem_cache_free(), causing a use-after-free.\n\nThis is the same class of bug as CVE-2026-23234 (which fixed the\nequivalent race in f2fs_write_end_io() in data.c), but in the\ncompressed writeback completion path that was not covered by that fix.\n\nFix this by moving dec_page_count() to after page_array_free(), so\nthat all sbi accesses complete before the counter decrement that can\nunblock unmount. For non-last folios (where atomic_dec_return on\ncic-\u003epending_pages is nonzero), dec_page_count is called immediately\nbefore returning \u2014 page_array_free is not reached on this path, so\nthere is no post-decrement sbi access. For the last folio,\npage_array_free runs while the F2FS_WB_CP_DATA counter is still\nnonzero (this folio has not yet decremented it), keeping sbi alive,\nand dec_page_count runs as the final operation.",
  "id": "GHSA-5c3m-p5m6-p659",
  "modified": "2026-05-06T21:31:31Z",
  "published": "2026-05-01T15:30:32Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31702"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2c97dcb6147c8f7f25c629b93be1e69617de5d4a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/39d4ee19c1e7d753dd655aebee632271b171f43a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c76cf339b87975ae5b2c06d2d774d5667d25a12a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ef57cd3329b40c739b9a2e1a8a21ecc4171c6280"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f5154cf3ce1c8193f0c1891d3769f62740cfe6fe"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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