{"id":"CVE-2026-23450","revision":"9e53034c41964a7880a50fe7603fe799","records":[{"revision":"9e53034c41964a7880a50fe7603fe799","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-23450","aliases":[],"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","state":0,"publishedAt":"2026-04-03T15:15:33.144+00:00","modifiedAt":"2026-10-19T18:35:44.407+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"net/smc/af_smc.c\",\n \"net/smc/smc.h\",\n \"net/smc/smc_close.c\"\n ],\n \"versions\": [\n {\n \"version\": \"ebfee3e153f67c8b38eb94a7062ee94aa6f92708\",\n \"lessThan\": \"f315277856caeafcd996c2611afc085ca2d53275\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"1e4f873879e075bbd4eb1c644d6933303ac5eba4\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"f00fc26c8a06442b225a350fe000c0a11483e6a3\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"cadf3da46c15523fba90d80c9955f536ee3b4023\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"1fab5ece76fb42a761178dcd0ebcbf578377b0dd\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"8270d9c21041470f58348248b9d9dcf3bf79592e\",\n \"lessThan\": \"6d5e4538364b9ceb1ac2941a4deb86650afb3538\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"5.15.174\",\n \"lessThan\": \"5.15.203\",\n \"status\": \"affected\",\n \"versionType\": \"semver\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"net/smc/af_smc.c\",\n \"net/smc/smc.h\",\n \"net/smc/smc_close.c\"\n ],\n \"versions\": [\n {\n \"version\": \"5.18\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"5.18\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.203\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.167\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.130\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.78\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.20\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.19.10\",\n \"lessThanOrEqual\": \"6.19.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.0\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8,"severity":"CRITICAL"}],"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"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23450","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-23450","identifiers":["CVE-2026-23450"]},"retained":false,"historicalAffected":[]}],"coverage":[]}