{"id":"CVE-2026-23450","state":"PUBLISHED","title":"net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock()\n\nSyzkaller reported a panic in smc_tcp_syn_recv_sock() [1].\n\nsmc_tcp_syn_recv_sock() is called in the TCP receive path\n(softirq) via icsk_af_ops->syn_recv_sock on the clcsock (TCP\nlistening socket). It reads sk_user_data to get the smc_sock\npointer. However, when the SMC listen socket is being closed\nconcurrently, smc_close_active() sets clcsock->sk_user_data\nto NULL under sk_callback_lock, and then the smc_sock itself\ncan be freed via sock_put() in smc_release().\n\nThis leads to two issues:\n\n1) NULL pointer dereference: sk_user_data is NULL when\n   accessed.\n2) Use-after-free: sk_user_data is read as non-NULL, but the\n   smc_sock is freed before its fields (e.g., queued_smc_hs,\n   ori_af_ops) are accessed.\n\nThe race window looks like this (the syzkaller crash [1]\ntriggers via the SYN cookie path: tcp_get_cookie_sock() ->\nsmc_tcp_syn_recv_sock(), but the normal tcp_check_req() path\nhas the same race):\n\n  CPU A (softirq)              CPU B (process ctx)\n\n  tcp_v4_rcv()\n    TCP_NEW_SYN_RECV:\n    sk = req->rsk_listener\n    sock_hold(sk)\n    /* No lock on listener */\n                               smc_close_active():\n                                 write_lock_bh(cb_lock)\n                                 sk_user_data = NULL\n                                 write_unlock_bh(cb_lock)\n                                 ...\n                                 smc_clcsock_release()\n                                 sock_put(smc->sk) x2\n                                   -> smc_sock freed!\n    tcp_check_req()\n      smc_tcp_syn_recv_sock():\n        smc = user_data(sk)\n          -> NULL or dangling\n        smc->queued_smc_hs\n          -> crash!\n\nNote that the clcsock and smc_sock are two independent objects\nwith separate refcounts. TCP stack holds a reference on the\nclcsock, which keeps it alive, but this does NOT prevent the\nsmc_sock from being freed.\n\nFix this by using RCU and refcount_inc_not_zero() to safely\naccess smc_sock. Since smc_tcp_syn_recv_sock() is called in\nthe TCP three-way handshake path, taking read_lock_bh on\nsk_callback_lock is too heavy and would not survive a SYN\nflood attack. Using rcu_read_lock() is much more lightweight.\n\n- Set SOCK_RCU_FREE on the SMC listen socket so that\n  smc_sock freeing is deferred until after the RCU grace\n  period. This guarantees the memory is still valid when\n  accessed inside rcu_read_lock().\n- Use rcu_read_lock() to protect reading sk_user_data.\n- Use refcount_inc_not_zero(&smc->sk.sk_refcnt) to pin the\n  smc_sock. If the refcount has already reached zero (close\n  path completed), it returns false and we bail out safely.\n\nNote: smc_hs_congested() has a similar lockless read of\nsk_user_data without rcu_read_lock(), but it only checks for\nNULL and accesses the global smc_hs_wq, never dereferencing\nany smc_sock field, so it is not affected.\n\nReproducer was verified with mdelay injection and smc_run,\nthe issue no longer occurs with this patch applied.\n\n[1] https://syzkaller.appspot.com/bug?extid=827ae2bfb3a3529333e9","publishedAt":"2026-04-03T15:15:33.144Z","updatedAt":"2026-10-19T18:35:44.407Z","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":"ebfee3e153f67c8b38eb94a7062ee94aa6f92708","status":"affected","lessThan":"f315277856caeafcd996c2611afc085ca2d53275","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"1e4f873879e075bbd4eb1c644d6933303ac5eba4","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"f00fc26c8a06442b225a350fe000c0a11483e6a3","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"cadf3da46c15523fba90d80c9955f536ee3b4023","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"1fab5ece76fb42a761178dcd0ebcbf578377b0dd","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"6d5e4538364b9ceb1ac2941a4deb86650afb3538","versionType":"git"},{"version":"5.15.174","status":"affected","lessThan":"5.15.203","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/af_smc.c","net/smc/smc.h","net/smc/smc_close.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.20","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.10","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/af_smc.c","net/smc/smc.h","net/smc/smc_close.c"]}],"references":["https://git.kernel.org/stable/c/f315277856caeafcd996c2611afc085ca2d53275","https://git.kernel.org/stable/c/1e4f873879e075bbd4eb1c644d6933303ac5eba4","https://git.kernel.org/stable/c/f00fc26c8a06442b225a350fe000c0a11483e6a3","https://git.kernel.org/stable/c/cadf3da46c15523fba90d80c9955f536ee3b4023","https://git.kernel.org/stable/c/fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2","https://git.kernel.org/stable/c/1fab5ece76fb42a761178dcd0ebcbf578377b0dd","https://git.kernel.org/stable/c/6d5e4538364b9ceb1ac2941a4deb86650afb3538","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":["CWE-362"],"ingestedAt":"2026-10-29T20:11:21.040Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/23xxx/CVE-2026-23450.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-23450","state":"PUBLISHED","datePublished":"2026-04-03T15:15:33.144Z","dateUpdated":"2026-10-19T18:35:44.407Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-01-13T15:37:46.020Z"},"containers":{"cna":{"title":"net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock()\n\nSyzkaller reported a panic in smc_tcp_syn_recv_sock() [1].\n\nsmc_tcp_syn_recv_sock() is called in the TCP receive path\n(softirq) via icsk_af_ops->syn_recv_sock on the clcsock (TCP\nlistening socket). It reads sk_user_data to get the smc_sock\npointer. However, when the SMC listen socket is being closed\nconcurrently, smc_close_active() sets clcsock->sk_user_data\nto NULL under sk_callback_lock, and then the smc_sock itself\ncan be freed via sock_put() in smc_release().\n\nThis leads to two issues:\n\n1) NULL pointer dereference: sk_user_data is NULL when\n   accessed.\n2) Use-after-free: sk_user_data is read as non-NULL, but the\n   smc_sock is freed before its fields (e.g., queued_smc_hs,\n   ori_af_ops) are accessed.\n\nThe race window looks like this (the syzkaller crash [1]\ntriggers via the SYN cookie path: tcp_get_cookie_sock() ->\nsmc_tcp_syn_recv_sock(), but the normal tcp_check_req() path\nhas the same race):\n\n  CPU A (softirq)              CPU B (process ctx)\n\n  tcp_v4_rcv()\n    TCP_NEW_SYN_RECV:\n    sk = req->rsk_listener\n    sock_hold(sk)\n    /* No lock on listener */\n                               smc_close_active():\n                                 write_lock_bh(cb_lock)\n                                 sk_user_data = NULL\n                                 write_unlock_bh(cb_lock)\n                                 ...\n                                 smc_clcsock_release()\n                                 sock_put(smc->sk) x2\n                                   -> smc_sock freed!\n    tcp_check_req()\n      smc_tcp_syn_recv_sock():\n        smc = user_data(sk)\n          -> NULL or dangling\n        smc->queued_smc_hs\n          -> crash!\n\nNote that the clcsock and smc_sock are two independent objects\nwith separate refcounts. TCP stack holds a reference on the\nclcsock, which keeps it alive, but this does NOT prevent the\nsmc_sock from being freed.\n\nFix this by using RCU and refcount_inc_not_zero() to safely\naccess smc_sock. Since smc_tcp_syn_recv_sock() is called in\nthe TCP three-way handshake path, taking read_lock_bh on\nsk_callback_lock is too heavy and would not survive a SYN\nflood attack. Using rcu_read_lock() is much more lightweight.\n\n- Set SOCK_RCU_FREE on the SMC listen socket so that\n  smc_sock freeing is deferred until after the RCU grace\n  period. This guarantees the memory is still valid when\n  accessed inside rcu_read_lock().\n- Use rcu_read_lock() to protect reading sk_user_data.\n- Use refcount_inc_not_zero(&smc->sk.sk_refcnt) to pin the\n  smc_sock. If the refcount has already reached zero (close\n  path completed), it returns false and we bail out safely.\n\nNote: smc_hs_congested() has a similar lockless read of\nsk_user_data without rcu_read_lock(), but it only checks for\nNULL and accesses the global smc_hs_wq, never dereferencing\nany smc_sock field, so it is not affected.\n\nReproducer was verified with mdelay injection and smc_run,\nthe issue no longer occurs with this patch applied.\n\n[1] https://syzkaller.appspot.com/bug?extid=827ae2bfb3a3529333e9"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"ebfee3e153f67c8b38eb94a7062ee94aa6f92708","status":"affected","lessThan":"f315277856caeafcd996c2611afc085ca2d53275","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"1e4f873879e075bbd4eb1c644d6933303ac5eba4","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"f00fc26c8a06442b225a350fe000c0a11483e6a3","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"cadf3da46c15523fba90d80c9955f536ee3b4023","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"1fab5ece76fb42a761178dcd0ebcbf578377b0dd","versionType":"git"},{"version":"8270d9c21041470f58348248b9d9dcf3bf79592e","status":"affected","lessThan":"6d5e4538364b9ceb1ac2941a4deb86650afb3538","versionType":"git"},{"version":"5.15.174","status":"affected","lessThan":"5.15.203","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/af_smc.c","net/smc/smc.h","net/smc/smc_close.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.18","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.167","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.130","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.20","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.10","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/smc/af_smc.c","net/smc/smc.h","net/smc/smc_close.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/f315277856caeafcd996c2611afc085ca2d53275"},{"url":"https://git.kernel.org/stable/c/1e4f873879e075bbd4eb1c644d6933303ac5eba4"},{"url":"https://git.kernel.org/stable/c/f00fc26c8a06442b225a350fe000c0a11483e6a3"},{"url":"https://git.kernel.org/stable/c/cadf3da46c15523fba90d80c9955f536ee3b4023"},{"url":"https://git.kernel.org/stable/c/fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2"},{"url":"https://git.kernel.org/stable/c/1fab5ece76fb42a761178dcd0ebcbf578377b0dd"},{"url":"https://git.kernel.org/stable/c/6d5e4538364b9ceb1ac2941a4deb86650afb3538"}],"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 callback is invoked from the TCP receive path via tcp_check_req() or tcp_get_cookie_sock() for packets hitting an SMC listening socket. A remote peer can reach this pre-authentication code by completing or racing TCP handshakes to the exposed listener.\nAC:L - The trigger is a close-vs-handshake race, but the attacker can drive the packet side repeatedly with concurrent connection attempts and SYN-cookie/normal ACK paths. There is no rare memory layout, special authentication state, or non-default runtime condition required beyond an enabled SMC listener.\nPR:N - No kernel capability, local account, or SMC protocol authentication is checked before smc_tcp_syn_recv_sock() dereferences sk_user_data. The network peer reaches the vulnerable path before accept-time SMC CLC processing.\nUI:N - Exploitation does not require a victim user action once an SMC listener is present. Incoming network traffic and concurrent listener teardown are sufficient to hit the vulnerable path.\nS:U - The bug corrupts or crashes kernel state within the same host security authority. It is not a VM escape, IOMMU bypass, or cross-scope boundary violation.\nC:H - The fix addresses a real use-after-free of struct smc_sock, not only a NULL dereference. Under the required kernel guidance, UAF is treated as enabling high confidentiality impact through potential reuse and disclosure primitives.\nI:H - The dangling smc_sock is dereferenced for fields including queued_smc_hs and ori_af_ops, and UAF of kernel heap objects can be shaped into control-flow or write primitives. Under the required kernel guidance, UAF warrants high integrity impact.\nA:H - The observed failure is a KASAN NULL dereference/oops in smc_tcp_syn_recv_sock(), and the UAF path can also crash the kernel. Kernel oops or panic is high availability 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S7-1500 CPU 1518-4 PN/DP MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.6","status":"affected","lessThan":"*","versionType":"custom"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.5","status":"affected","lessThan":"*","versionType":"custom"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.7","status":"affected","lessThan":"*","versionType":"custom"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.6","status":"affected","lessThan":"*","versionType":"custom"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.5","status":"affected","lessThan":"*","versionType":"custom"}]},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP 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MFP","defaultStatus":"unknown","versions":[{"version":"V3.1.7","status":"affected","lessThan":"*","versionType":"custom"}]}],"references":[{"url":"https://cert-portal.siemens.com/productcert/html/ssa-082556.html"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html"}],"providerMetadata":{"shortName":"siemens-SADP","orgId":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","dateUpdated":"2026-10-15T01:15:11.305Z"},"x_adpType":"supplier"},{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-23450","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:08:20.612438Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-362","lang":"en","type":"CWE","description":"CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T18:35:44.407Z"}}]}}}