--- id: CVE-2026-23450 title: |- In the Linux kernel, the following vulnerability has been resolved: net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock() Syzkaller reported a panic in smc_tcp_syn_recv_sock() [1]. smc_tcp_syn_recv_sock() is called in the T… summary: |- In the Linux kernel, the following vulnerability has been resolved: net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock() Syzkaller reported a panic in smc_tcp_syn_recv_sock() [1]. smc_tcp_syn_recv_sock() is called in the T… severity: critical cvss: 9.8 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H' cwe: - CWE-416 vendor: linux product: linux_kernel affected: - 'linux_kernel >= 5.15.174, < 5.15.203' - 'linux_kernel >= 5.18, < 6.1.167' - 'linux_kernel >= 6.2, < 6.6.130' - 'linux_kernel >= 6.7, < 6.12.78' - 'linux_kernel >= 6.13, < 6.18.20' - 'linux_kernel >= 6.19, < 6.19.10' - linux_kernel = 7.0 patched: - linux_kernel 6.19.10 published: '2026-04-03' updated: '2026-10-15' sourceUpdated: '2026-10-15T02:18:57.757' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-23450' references: - url: 'https://git.kernel.org/stable/c/1e4f873879e075bbd4eb1c644d6933303ac5eba4' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/1fab5ece76fb42a761178dcd0ebcbf578377b0dd' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/6d5e4538364b9ceb1ac2941a4deb86650afb3538' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/cadf3da46c15523fba90d80c9955f536ee3b4023' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/f00fc26c8a06442b225a350fe000c0a11483e6a3' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/f315277856caeafcd996c2611afc085ca2d53275' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e tags: - nvd - cve.org epss: 0.00444 epssPercentile: 0.38408 ingestedAt: '2026-09-08T15:33:26.992Z' ssvc: exploitation: none automatable: 'yes' technicalImpact: total timestamp: '2026-10-16T15:08:20.612438Z' --- ## Overview In the Linux kernel, the following vulnerability has been resolved: net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock() Syzkaller reported a panic in smc_tcp_syn_recv_sock() [1]. smc_tcp_syn_recv_sock() is called in the TCP receive path (softirq) via icsk_af_ops->syn_recv_sock on the clcsock (TCP listening socket). It reads sk_user_data to get the smc_sock pointer. However, when the SMC listen socket is being closed concurrently, smc_close_active() sets clcsock->sk_user_data to NULL under sk_callback_lock, and then the smc_sock itself can be freed via sock_put() in smc_release(). This leads to two issues: 1) NULL pointer dereference: sk_user_data is NULL when accessed. 2) Use-after-free: sk_user_data is read as non-NULL, but the smc_sock is freed before its fields (e.g., queued_smc_hs, ori_af_ops) are accessed. The race window looks like this (the syzkaller crash [1] triggers via the SYN cookie path: tcp_get_cookie_sock() -> smc_tcp_syn_recv_sock(), but the normal tcp_check_req() path has the same race): CPU A (softirq) CPU B (process ctx) tcp_v4_rcv() TCP_NEW_SYN_RECV: sk = req->rsk_listener sock_hold(sk) /* No lock on listener */ smc_close_active(): write_lock_bh(cb_lock) sk_user_data = NULL write_unlock_bh(cb_lock) ... smc_clcsock_release() sock_put(smc->sk) x2 -> smc_sock freed! tcp_check_req() smc_tcp_syn_recv_sock(): smc = user_data(sk) -> NULL or dangling smc->queued_smc_hs -> crash! Note that the clcsock and smc_sock are two independent objects with separate refcounts. TCP stack holds a reference on the clcsock, which keeps it alive, but this does NOT prevent the smc_sock from being freed. Fix this by using RCU and refcount_inc_not_zero() to safely access smc_sock. Since smc_tcp_syn_recv_sock() is called in the TCP three-way handshake path, taking read_lock_bh on sk_callback_lock is too heavy and would not survive a SYN flood attack. Using rcu_read_lock() is much more lightweight. - Set SOCK_RCU_FREE on the SMC listen socket so that smc_sock freeing is deferred until after the RCU grace period. This guarantees the memory is still valid when accessed inside rcu_read_lock(). - Use rcu_read_lock() to protect reading sk_user_data. - Use refcount_inc_not_zero(&smc->sk.sk_refcnt) to pin the smc_sock. If the refcount has already reached zero (close path completed), it returns false and we bail out safely. Note: smc_hs_congested() has a similar lockless read of sk_user_data without rcu_read_lock(), but it only checks for NULL and accesses the global smc_hs_wq, never dereferencing any smc_sock field, so it is not affected. Reproducer was verified with mdelay injection and smc_run, the issue no longer occurs with this patch applied. [1] https://syzkaller.appspot.com/bug?extid=827ae2bfb3a3529333e9 ## Affected - `linux_kernel >= 5.15.174, < 5.15.203` - `linux_kernel >= 5.18, < 6.1.167` - `linux_kernel >= 6.2, < 6.6.130` - `linux_kernel >= 6.7, < 6.12.78` - `linux_kernel >= 6.13, < 6.18.20` - `linux_kernel >= 6.19, < 6.19.10` - `linux_kernel = 7.0` ## Remediation Upgrade past the affected range: - `linux_kernel 6.19.10`