{"id":"CVE-2026-98104","state":"PUBLISHED","title":"net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_u32: fix duplicate handle when node ID pool is exhausted\n\ngen_new_kid() falls back to returning max (htid | 0xFFF) when both\nidr_alloc_u32() ranges are full, instead of reporting an error.\nu32_change() trusts that value and inserts a new knode with a handle\nthat is already live in the hash table, breaking handle uniqueness\nwithin the table's node ID space.\n\nThe handle was never reserved in ht->handle_idr, so every later error\npath that does idr_remove(&ht->handle_idr, handle) removes the\nreservation of a different, live knode, which is then reused — one\nfailed add compounds into further duplicates.\n\nThe 4095 limit is per (table, bucket) — ht->handle_idr is per hash\ntable and the range is derived from htid (bucketid), so a table with\ndivisor 256 can legitimately hold 256*4095 knodes.\n\nThe sibling helper gen_new_htid() has the same silent in-band failure:\nit returns 0 when the tp_c handle pool (1..0x7FF) is full, and\nu32_init() publishes the root hash table with handle 0 without\nchecking.  Two root tables with handle 0 alias in u32_lookup_ht(),\nallowing cross-tcf_proto knode add/lookup/delete.  Add the same\nexhaustion check that the divisor path already has.\n\nReturn an error so u32_change() fails with ENOSPC/ENOMEM when the\nnode ID space is exhausted, and so u32_init() fails with -ENOMEM\nwhen the hash table ID space is exhausted.  The extack message\ndistinguishes pool exhaustion (-ENOSPC) from a transient allocation\nfailure (-ENOMEM).\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED=y, CONFIG_CLS_U32=y (or =m with module loaded)\n- Create a clsact qdisc on a device, then add 4095 u32 filters with\n  auto-generated handles to fill the node ID space for the root hash\n  table (single bucket). The 4096th auto-handle filter add triggers\n  the duplicate handle (fh 800::fff reused). Reachable at Level 2\n  (unshare -Urn, namespace-local CAP_NET_ADMIN).\n- For gen_new_htid: create 2047 u32 proto entries on the same block\n  to fill the tp_c handle pool, then create one more. The root table\n  gets handle 0 and aliases with other handle-0 root tables.","publishedAt":"2026-09-25T10:35:54.544Z","updatedAt":"2026-10-19T09:13:56.808Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"f4ee13ed7f7b22dcd8287fcf477ae37bd84567da","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"84223baf21bc9b008444ae9bc38d5fb91fe00b9d","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"6890e28840bae4f6805e8de981c4ec8e12a4e064","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"feab9261b537df4ebb8350e4779bc185373059fd","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"f594f04268d01c5fdc975f3f51fc219ea2159ac6","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_u32.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.16","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_u32.c"]}],"references":["https://git.kernel.org/stable/c/f4ee13ed7f7b22dcd8287fcf477ae37bd84567da","https://git.kernel.org/stable/c/84223baf21bc9b008444ae9bc38d5fb91fe00b9d","https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064","https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd","https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6","https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98104.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98104","state":"PUBLISHED","datePublished":"2026-09-25T10:35:54.544Z","dateUpdated":"2026-10-19T09:13:56.808Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.315Z"},"containers":{"cna":{"title":"net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_u32: fix duplicate handle when node ID pool is exhausted\n\ngen_new_kid() falls back to returning max (htid | 0xFFF) when both\nidr_alloc_u32() ranges are full, instead of reporting an error.\nu32_change() trusts that value and inserts a new knode with a handle\nthat is already live in the hash table, breaking handle uniqueness\nwithin the table's node ID space.\n\nThe handle was never reserved in ht->handle_idr, so every later error\npath that does idr_remove(&ht->handle_idr, handle) removes the\nreservation of a different, live knode, which is then reused — one\nfailed add compounds into further duplicates.\n\nThe 4095 limit is per (table, bucket) — ht->handle_idr is per hash\ntable and the range is derived from htid (bucketid), so a table with\ndivisor 256 can legitimately hold 256*4095 knodes.\n\nThe sibling helper gen_new_htid() has the same silent in-band failure:\nit returns 0 when the tp_c handle pool (1..0x7FF) is full, and\nu32_init() publishes the root hash table with handle 0 without\nchecking.  Two root tables with handle 0 alias in u32_lookup_ht(),\nallowing cross-tcf_proto knode add/lookup/delete.  Add the same\nexhaustion check that the divisor path already has.\n\nReturn an error so u32_change() fails with ENOSPC/ENOMEM when the\nnode ID space is exhausted, and so u32_init() fails with -ENOMEM\nwhen the hash table ID space is exhausted.  The extack message\ndistinguishes pool exhaustion (-ENOSPC) from a transient allocation\nfailure (-ENOMEM).\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED=y, CONFIG_CLS_U32=y (or =m with module loaded)\n- Create a clsact qdisc on a device, then add 4095 u32 filters with\n  auto-generated handles to fill the node ID space for the root hash\n  table (single bucket). The 4096th auto-handle filter add triggers\n  the duplicate handle (fh 800::fff reused). Reachable at Level 2\n  (unshare -Urn, namespace-local CAP_NET_ADMIN).\n- For gen_new_htid: create 2047 u32 proto entries on the same block\n  to fill the tp_c handle pool, then create one more. The root table\n  gets handle 0 and aliases with other handle-0 root tables."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"f4ee13ed7f7b22dcd8287fcf477ae37bd84567da","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"84223baf21bc9b008444ae9bc38d5fb91fe00b9d","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"6890e28840bae4f6805e8de981c4ec8e12a4e064","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"feab9261b537df4ebb8350e4779bc185373059fd","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"f594f04268d01c5fdc975f3f51fc219ea2159ac6","versionType":"git"},{"version":"7801db8aec957fa6610efe0ee26a6c8bc0f1d73b","status":"affected","lessThan":"d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_u32.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.16","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_u32.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/f4ee13ed7f7b22dcd8287fcf477ae37bd84567da"},{"url":"https://git.kernel.org/stable/c/84223baf21bc9b008444ae9bc38d5fb91fe00b9d"},{"url":"https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064"},{"url":"https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd"},{"url":"https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6"},{"url":"https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T09:13:56.808Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.16","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}