CRITICAL: CVE-2026-23450 (CVSS 9.8) — multiple products

CVE: CVE-2026-23450

CVSS: 9.8 (3.1) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity: CRITICAL

Status: Critical advisory

Affected

_See vendor advisory_

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 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

Verified Sources

• NVD entry
• GitHub Advisory
• MITRE

References

• https://git.kernel.org/stable/c/1e4f873879e075bbd4eb1c644d6933303ac5eba4
• https://git.kernel.org/stable/c/1fab5ece76fb42a761178dcd0ebcbf578377b0dd
• https://git.kernel.org/stable/c/6d5e4538364b9ceb1ac2941a4deb86650afb3538
• https://git.kernel.org/stable/c/cadf3da46c15523fba90d80c9955f536ee3b4023
• https://git.kernel.org/stable/c/f00fc26c8a06442b225a350fe000c0a11483e6a3
• https://git.kernel.org/stable/c/f315277856caeafcd996c2611afc085ca2d53275
• https://git.kernel.org/stable/c/fd7579f0a2c84ba8a7d4f206201b50dc8ddf90c2

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_Validated by the Lyrie Threat Intelligence Pipeline — 3 independent sources confirmed before publication. No speculation._