{"id":"CVE-2026-64541","state":"PUBLISHED","title":"net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket\n\nsmc_cdc_rx_handler() looks up the connection by token under the link\ngroup's conns_lock, drops the lock, and then dereferences conn and the\nsmc_sock derived from it, ending in sock_hold(&smc->sk) inside\nsmc_cdc_msg_recv(). No reference is held across the lock release.\n\nThe only reference pinning the socket while the connection is\ndiscoverable in the link group is taken in smc_lgr_register_conn()\n(sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both\nunder conns_lock. Once the handler drops conns_lock, a concurrent\nclose() -> smc_release() -> smc_conn_free() -> smc_lgr_unregister_conn()\ncan drop that reference and free the smc_sock, so the handler's later\nsock_hold() runs on freed memory:\n\n  WARNING: lib/refcount.c:25 at refcount_warn_saturate\n  Workqueue: rxe_wq do_work\n   refcount_warn_saturate (lib/refcount.c:25)\n   smc_cdc_msg_recv (net/smc/smc_cdc.c:430)\n   smc_cdc_rx_handler (net/smc/smc_cdc.c:502)\n   smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445)\n   tasklet_action_common (kernel/softirq.c:938)\n   handle_softirqs (kernel/softirq.c:622)\n  Kernel panic - not syncing: panic_on_warn set\n\nOnly SMC-R is affected. The SMC-D receive tasklet is stopped by\ntasklet_kill(&conn->rx_tsklet) in smc_conn_free() before the connection\nis unregistered, so it cannot run concurrently with the free.\n\nTake the socket reference while still holding conns_lock, so the\nregistration reference can no longer be the last one, and drop it once\nthe handler is done.","publishedAt":"2026-07-27T20:10:34.439Z","updatedAt":"2026-10-19T20:48:39.587Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"8de4f665d0febfb92803dece377791a563fc7041","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"8145b432136285e01091815b48ceb2dae261f262","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"1951bffbc6493ec34cff3956b29d4bc6606904a6","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"647b19e5cc145a2f1f685ae8ff3805a17356888c","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"472e9d7c0d5b03be3ff91ff941f57da822b031bc","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"ce5aa8084329351086894aa34d77e40301d5bd3d","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"9d160b35cc34a2ba8229d07651468a7848325135","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/smc_cdc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.18","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/smc_cdc.c"]}],"references":["https://git.kernel.org/stable/c/8de4f665d0febfb92803dece377791a563fc7041","https://git.kernel.org/stable/c/8145b432136285e01091815b48ceb2dae261f262","https://git.kernel.org/stable/c/1951bffbc6493ec34cff3956b29d4bc6606904a6","https://git.kernel.org/stable/c/647b19e5cc145a2f1f685ae8ff3805a17356888c","https://git.kernel.org/stable/c/472e9d7c0d5b03be3ff91ff941f57da822b031bc","https://git.kernel.org/stable/c/3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb","https://git.kernel.org/stable/c/ce5aa8084329351086894aa34d77e40301d5bd3d","https://git.kernel.org/stable/c/9d160b35cc34a2ba8229d07651468a7848325135"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/64xxx/CVE-2026-64541.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-64541","state":"PUBLISHED","datePublished":"2026-07-27T20:10:34.439Z","dateUpdated":"2026-10-19T20:48:39.587Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T15:36:31.795Z"},"containers":{"cna":{"title":"net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket\n\nsmc_cdc_rx_handler() looks up the connection by token under the link\ngroup's conns_lock, drops the lock, and then dereferences conn and the\nsmc_sock derived from it, ending in sock_hold(&smc->sk) inside\nsmc_cdc_msg_recv(). No reference is held across the lock release.\n\nThe only reference pinning the socket while the connection is\ndiscoverable in the link group is taken in smc_lgr_register_conn()\n(sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both\nunder conns_lock. Once the handler drops conns_lock, a concurrent\nclose() -> smc_release() -> smc_conn_free() -> smc_lgr_unregister_conn()\ncan drop that reference and free the smc_sock, so the handler's later\nsock_hold() runs on freed memory:\n\n  WARNING: lib/refcount.c:25 at refcount_warn_saturate\n  Workqueue: rxe_wq do_work\n   refcount_warn_saturate (lib/refcount.c:25)\n   smc_cdc_msg_recv (net/smc/smc_cdc.c:430)\n   smc_cdc_rx_handler (net/smc/smc_cdc.c:502)\n   smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445)\n   tasklet_action_common (kernel/softirq.c:938)\n   handle_softirqs (kernel/softirq.c:622)\n  Kernel panic - not syncing: panic_on_warn set\n\nOnly SMC-R is affected. The SMC-D receive tasklet is stopped by\ntasklet_kill(&conn->rx_tsklet) in smc_conn_free() before the connection\nis unregistered, so it cannot run concurrently with the free.\n\nTake the socket reference while still holding conns_lock, so the\nregistration reference can no longer be the last one, and drop it once\nthe handler is done."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"8de4f665d0febfb92803dece377791a563fc7041","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"8145b432136285e01091815b48ceb2dae261f262","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"1951bffbc6493ec34cff3956b29d4bc6606904a6","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"647b19e5cc145a2f1f685ae8ff3805a17356888c","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"472e9d7c0d5b03be3ff91ff941f57da822b031bc","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"ce5aa8084329351086894aa34d77e40301d5bd3d","versionType":"git"},{"version":"d7b0e37c1ac152905b18a5b9506179091a35b0b6","status":"affected","lessThan":"9d160b35cc34a2ba8229d07651468a7848325135","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/smc_cdc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.18","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/smc_cdc.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/8de4f665d0febfb92803dece377791a563fc7041"},{"url":"https://git.kernel.org/stable/c/8145b432136285e01091815b48ceb2dae261f262"},{"url":"https://git.kernel.org/stable/c/1951bffbc6493ec34cff3956b29d4bc6606904a6"},{"url":"https://git.kernel.org/stable/c/647b19e5cc145a2f1f685ae8ff3805a17356888c"},{"url":"https://git.kernel.org/stable/c/472e9d7c0d5b03be3ff91ff941f57da822b031bc"},{"url":"https://git.kernel.org/stable/c/3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb"},{"url":"https://git.kernel.org/stable/c/ce5aa8084329351086894aa34d77e40301d5bd3d"},{"url":"https://git.kernel.org/stable/c/9d160b35cc34a2ba8229d07651468a7848325135"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The vulnerable handler is driven entirely by a CDC control message sent by the remote SMC-R peer over the RDMA link, with an attacker-chosen `token` field and no local syscall involvement. SMC-R runs over RoCEv2 (IP/UDP-routable, port 4791) with the CLC handshake over plain TCP, and SMC-Rv2 explicitly supports non-local/routed peers, so the attacker need not share an L2 segment.\nAC:L - The attacker controls both sides of the race: it chooses when to emit CDC messages and which connection to target (the alert token is disclosed to it in the CLC accept/confirm), and it can drive the teardown side itself via CDC close/abort flags into `smc_close_passive_work()` or a stale seqno with `failover_validation` into `abort_work` -> `smc_conn_kill()`. The race can be retried indefinitely across many connections in the same link group, and was reproduced in practice with soft-RoCE.\nPR:N - Establishing an SMC-R connection to a listening SMC socket requires no credentials — SMC has no authentication layer of its own, exactly like plain TCP. Everything after connection establishment (sending CDC messages with a chosen token, signalling close/abort) is available to an unauthenticated peer.\nUI:N - The CDC message is processed in a softirq tasklet from the RDMA completion queue with no involvement from any local user or application action. No victim interaction of any kind is needed.\nS:U - The corruption is confined to kernel memory within the same security authority; there is no VM, IOMMU, or sandbox boundary crossed. This is a standard in-kernel use-after-free.\nC:H - The freed `smc_sock` is reused type-safely as another live socket, so attacker-supplied cursors applied by `smc_cdc_msg_recv_action()` break the `0 <= bytes_to_rcv <= rmb_desc->len` invariant and make `smc_rx_recvmsg()` hand stale RMB contents to userspace, while the urgent-data path reads `*(base + conn->urg_curs.count - 1)` at an attacker-chosen offset. Once the slab page is reclaimed after the RCU grace period, reuse is unconstrained, giving a general kernel-memory read primitive.\nI:H - `sock_hold()` on an already-zero refcount followed by `sock_put()` re-enters `sk_free()`, yielding a double free, and the handler additionally writes `sk_err`/`sk_shutdown`, makes indirect calls through `sk_data_ready()`/`sk_write_space()`, and `queue_work()`s a freed `work_struct`. These are classic heap-spray and control-flow-hijack primitives leading to arbitrary kernel write.\nA:H - The reported symptom is `refcount_warn_saturate` from `smc_cdc_msg_recv()`, which is an immediate kernel panic on `panic_on_warn` systems, and dereferencing freed memory in softirq context otherwise oopses. The attacker can trigger it repeatedly without authentication."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T04:57:17.774Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"5.10.261"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"5.15.212"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"6.1.178"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"6.6.145"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.18","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-64541","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:42:09.809089Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","lang":"en","type":"CWE","description":"CWE-416 Use After Free"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:48:39.587Z"}}]}}}