CVE-2024-26958 (GCVE-0-2024-26958)
Vulnerability from cvelistv5
Published
2024-05-01 05:19
Modified
2026-08-05 11:28
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: nfs: fix UAF in direct writes In production we have been hitting the following warning consistently ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 17 PID: 1800359 at lib/refcount.c:28 refcount_warn_saturate+0x9c/0xe0 Workqueue: nfsiod nfs_direct_write_schedule_work [nfs] RIP: 0010:refcount_warn_saturate+0x9c/0xe0 PKRU: 55555554 Call Trace: <TASK> ? __warn+0x9f/0x130 ? refcount_warn_saturate+0x9c/0xe0 ? report_bug+0xcc/0x150 ? handle_bug+0x3d/0x70 ? exc_invalid_op+0x16/0x40 ? asm_exc_invalid_op+0x16/0x20 ? refcount_warn_saturate+0x9c/0xe0 nfs_direct_write_schedule_work+0x237/0x250 [nfs] process_one_work+0x12f/0x4a0 worker_thread+0x14e/0x3b0 ? ZSTD_getCParams_internal+0x220/0x220 kthread+0xdc/0x120 ? __btf_name_valid+0xa0/0xa0 ret_from_fork+0x1f/0x30 This is because we're completing the nfs_direct_request twice in a row. The source of this is when we have our commit requests to submit, we process them and send them off, and then in the completion path for the commit requests we have if (nfs_commit_end(cinfo.mds)) nfs_direct_write_complete(dreq); However since we're submitting asynchronous requests we sometimes have one that completes before we submit the next one, so we end up calling complete on the nfs_direct_request twice. The only other place we use nfs_generic_commit_list() is in __nfs_commit_inode, which wraps this call in a nfs_commit_begin(); nfs_commit_end(); Which is a common pattern for this style of completion handling, one that is also repeated in the direct code with get_dreq()/put_dreq() calls around where we process events as well as in the completion paths. Fix this by using the same pattern for the commit requests. Before with my 200 node rocksdb stress running this warning would pop every 10ish minutes. With my patch the stress test has been running for several hours without popping.
References
Impacted products
Vendor Product Version
Linux Linux Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
Version: af7cf057933f01dc7f33ddfb5e436ad598ed17ad
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the attacker must issue the direct I/O locally even though a remote NFS/pNFS data server influences the reply timing.\\nAC:L - The attacker controls the race by submitting large numbers of concurrent asynchronous O_DIRECT writes via io_submit(), each generating multiple per-bucket pNFS commit RPCs, and can loop indefinitely at no cost; in the worst-case deployment a hostile NFS server also controls COMMIT reply timing, and the bug reproduced roughly every ten minutes under ordinary production load.\\nPR:L - Only an unprivileged local user with write access to any file on an existing NFS mount is required \\u2014 O_DIRECT needs no capability and there is no privilege gate anywhere on the path, a routine situation with NFS home directories, HPC clusters, and NFS-backed container volumes.\\nUI:N - The attacker\u0027s own write syscalls trigger the double completion; no victim action is needed since the NFS mount is pre-existing infrastructure rather than something a user must be induced to set up.\\nS:U - The corruption is confined to kernel memory managed by the same security authority as the NFS client; no VM, IOMMU, or sandbox boundary is crossed.\\nC:H - The freed nfs_direct_req is re-read by the second workqueue run (flags, inode, iocb) and the aio_kiocb is double-freed, giving a use-after-free read primitive over reclaimed slab memory that can be leveraged to disclose arbitrary kernel data.\\nI:H - The refcount underflow frees the object while still referenced, and the second run performs an indirect call through dreq-\u003eiocb-\u003eki_complete read from freed memory plus a double aio_complete/double-free \\u2014 heap corruption and control-flow hijack primitives suitable for privilege escalation.\\nA:H - The bug produces refcount_t underflow warnings, oopses, and slab corruption, and the duplicated inode_dio_end() underflows i_dio_count so inode_dio_wait() hangs truncate/setattr on that inode indefinitely.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"6cd3f13aaa62970b5169d990e936b2e96943bc6a\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"80d24b308b7ee7037fc90d8ac99f6f78df0a256f\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"3abc2d160ed8213948b147295d77d44a22c88fa3\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"e25447c35f8745337ea8bc0c9697fcac14df8605\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"1daf52b5ffb24870fbeda20b4967526d8f9e12ab\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"cf54f66e1dd78990ec6b32177bca7e6ea2144a95\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"af7cf057933f01dc7f33ddfb5e436ad598ed17ad\", \"lessThan\": \"17f46b803d4f23c66cacce81db35fef3adb8f2af\", \"versionType\": \"git\"}], \"programFiles\": [\"fs/nfs/direct.c\", \"fs/nfs/write.c\", \"include/linux/nfs_fs.h\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.5\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.5\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.4.297\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.4.*\"}, {\"status\": \"unaffected\", \"version\": \"5.10.215\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.154\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.84\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.24\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.7.12\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.7.*\"}, {\"status\": \"unaffected\", \"version\": \"6.8.3\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.8.*\"}, {\"status\": \"unaffected\", \"version\": \"6.9\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"fs/nfs/direct.c\", \"fs/nfs/write.c\", \"include/linux/nfs_fs.h\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/6cd3f13aaa62970b5169d990e936b2e96943bc6a\"}, {\"url\": \"https://git.kernel.org/stable/c/4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5\"}, {\"url\": \"https://git.kernel.org/stable/c/80d24b308b7ee7037fc90d8ac99f6f78df0a256f\"}, {\"url\": \"https://git.kernel.org/stable/c/3abc2d160ed8213948b147295d77d44a22c88fa3\"}, {\"url\": \"https://git.kernel.org/stable/c/e25447c35f8745337ea8bc0c9697fcac14df8605\"}, {\"url\": \"https://git.kernel.org/stable/c/1daf52b5ffb24870fbeda20b4967526d8f9e12ab\"}, {\"url\": \"https://git.kernel.org/stable/c/cf54f66e1dd78990ec6b32177bca7e6ea2144a95\"}, {\"url\": \"https://git.kernel.org/stable/c/17f46b803d4f23c66cacce81db35fef3adb8f2af\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnfs: fix UAF in direct writes\\n\\nIn production we have been hitting the following warning consistently\\n\\n------------[ cut here ]------------\\nrefcount_t: underflow; use-after-free.\\nWARNING: CPU: 17 PID: 1800359 at lib/refcount.c:28 refcount_warn_saturate+0x9c/0xe0\\nWorkqueue: nfsiod nfs_direct_write_schedule_work [nfs]\\nRIP: 0010:refcount_warn_saturate+0x9c/0xe0\\nPKRU: 55555554\\nCall Trace:\\n \u003cTASK\u003e\\n ? __warn+0x9f/0x130\\n ? refcount_warn_saturate+0x9c/0xe0\\n ? report_bug+0xcc/0x150\\n ? handle_bug+0x3d/0x70\\n ? exc_invalid_op+0x16/0x40\\n ? asm_exc_invalid_op+0x16/0x20\\n ? refcount_warn_saturate+0x9c/0xe0\\n nfs_direct_write_schedule_work+0x237/0x250 [nfs]\\n process_one_work+0x12f/0x4a0\\n worker_thread+0x14e/0x3b0\\n ? ZSTD_getCParams_internal+0x220/0x220\\n kthread+0xdc/0x120\\n ? __btf_name_valid+0xa0/0xa0\\n ret_from_fork+0x1f/0x30\\n\\nThis is because we\u0027re completing the nfs_direct_request twice in a row.\\n\\nThe source of this is when we have our commit requests to submit, we\\nprocess them and send them off, and then in the completion path for the\\ncommit requests we have\\n\\nif (nfs_commit_end(cinfo.mds))\\n\\tnfs_direct_write_complete(dreq);\\n\\nHowever since we\u0027re submitting asynchronous requests we sometimes have\\none that completes before we submit the next one, so we end up calling\\ncomplete on the nfs_direct_request twice.\\n\\nThe only other place we use nfs_generic_commit_list() is in\\n__nfs_commit_inode, which wraps this call in a\\n\\nnfs_commit_begin();\\nnfs_commit_end();\\n\\nWhich is a common pattern for this style of completion handling, one\\nthat is also repeated in the direct code with get_dreq()/put_dreq()\\ncalls around where we process events as well as in the completion paths.\\n\\nFix this by using the same pattern for the commit requests.\\n\\nBefore with my 200 node rocksdb stress running this warning would pop\\nevery 10ish minutes.  With my patch the stress test has been running for\\nseveral hours without popping.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.4.297\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.215\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.154\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.84\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.24\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.7.12\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.8.3\", \"versionStartIncluding\": \"4.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.9\", \"versionStartIncluding\": \"4.5\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T11:28:37.623Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2024-26958\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T11:28:37.623Z\", \"dateReserved\": \"2024-02-19T14:20:24.200Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-05-01T05:19:04.069Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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