CVE-2026-31702 (GCVE-0-2026-31702)

Vulnerability from cvelistv5 – Published: 2026-05-01 13:56 – Updated: 2026-05-01 13:56
VLAI?
Title
f2fs: fix use-after-free of sbi in f2fs_compress_write_end_io()
Summary
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 ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 4c8ff7095bef64fc47e996a938f7d57f9e077da3 , < ef57cd3329b40c739b9a2e1a8a21ecc4171c6280 (git)
Affected: 4c8ff7095bef64fc47e996a938f7d57f9e077da3 , < f5154cf3ce1c8193f0c1891d3769f62740cfe6fe (git)
Affected: 4c8ff7095bef64fc47e996a938f7d57f9e077da3 , < c76cf339b87975ae5b2c06d2d774d5667d25a12a (git)
Affected: 4c8ff7095bef64fc47e996a938f7d57f9e077da3 , < 2c97dcb6147c8f7f25c629b93be1e69617de5d4a (git)
Affected: 4c8ff7095bef64fc47e996a938f7d57f9e077da3 , < 39d4ee19c1e7d753dd655aebee632271b171f43a (git)
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    Linux Linux Affected: 5.6
Unaffected: 0 , < 5.6 (semver)
Unaffected: 6.6.136 , ≤ 6.6.* (semver)
Unaffected: 6.12.84 , ≤ 6.12.* (semver)
Unaffected: 6.18.25 , ≤ 6.18.* (semver)
Unaffected: 7.0.2 , ≤ 7.0.* (semver)
Unaffected: 7.1-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
            "fs/f2fs/compress.c"
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          "value": "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."
        }
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        "dateUpdated": "2026-05-01T13:56:01.601Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/f5154cf3ce1c8193f0c1891d3769f62740cfe6fe"
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        {
          "url": "https://git.kernel.org/stable/c/39d4ee19c1e7d753dd655aebee632271b171f43a"
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    "datePublished": "2026-05-01T13:56:01.601Z",
    "dateReserved": "2026-03-09T15:48:24.132Z",
    "dateUpdated": "2026-05-01T13:56:01.601Z",
    "state": "PUBLISHED"
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  }
}


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