# CVE-2026-23450: linux: In the Linux kernel, the following vulnerability has been resolved: net/smc: fix NULL dereference and UAF in smc_tcp... CVE-2026-23450 is fixed in 12 products on 1 platform, first by DEBIAN-CVE-2026-23450, released April 3, 2026. It is not reported as exploited. Patch Radar priority: Urgent. - Web page: https://patchblox.com/security/cve/CVE-2026-23450 - Priority: Urgent - CVSS: 9.8 (critical) - EPSS: 0.0046 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Apr 3, 2026 ## Description 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 ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | kernel-64kb sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-azure sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default sles 15.6 | 6.4.0-150600.23.112.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-default sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-default-base sles 15.6 | 6.4.0-150600.23.112.1.150600.12.52.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-default-base sles 15.7 | 6.4.0-150700.53.55.1.150700.17.33.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-docs sles 15.6 | 6.4.0-150600.23.112.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-docs sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-livepatch-SLE15-SP6_Update_26 sles 15.6 | 1-150600.13.3.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-livepatch-SLE15-SP7_Update_15 sles 15.7 | 1-150700.15.3.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-obs-build sles 15.6 | 6.4.0-150600.23.112.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-obs-build sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-source sles 15.6 | 6.4.0-150600.23.112.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-source sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-syms sles 15.6 | 6.4.0-150600.23.112.1 | [SUSE-SU-2026:2195-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2195-1.md) | Jul 1, 2026 | | Linux | kernel-syms sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | kernel-zfcpdump sles 15.7 | 6.4.0-150700.53.55.1 | [SUSE-SU-2026:2238-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2238-1.md) | Jun 30, 2026 | | Linux | linux Debian 12.15 (bookworm) | 6.1.170-1 | [DEBIAN-CVE-2026-23450](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23450.md) | Apr 3, 2026 | | Linux | linux Debian 13.5 (trixie) | 6.12.85-1 | [DEBIAN-CVE-2026-23450](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23450.md) | Apr 3, 2026 | | Linux | linux Debian 14 | 6.19.10-1 | [DEBIAN-CVE-2026-23450](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23450.md) | Apr 3, 2026 | --- Data as of 2026-11-09T01:18:40Z UTC. 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