CVE-2026-99032 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
net/smc: protect clcsock lifetime in smc_getname
smc_getname() dereferences smc->clcsock without holding clcsock_release_lock. Link-group termination can release the CLC socket through smc_close_active_abort() while the SMC socket is still open, for example after shutdown(SHUT_WR).
A getsockname() caller can load smc->clcsock, then the termination worker can clear the pointer and call sock_release() before the caller accesses clcsock->ops or invokes getname(). This causes a use-after-free; if the worker clears the pointer before the load, it causes a NULL dereference. The syscall's file reference keeps the SMC socket alive but does not prevent asynchronous release of its CLC socket.
KASAN reported the following with test-only timing instrumentation:
BUG: KASAN: slab-use-after-free in smc_getname+0x19e/0x1b0 Read of size 8 at addr ffff888109abb4e0 by task poc/103 Call Trace: smc_getname+0x19e/0x1b0 do_getsockname+0xe5/0x170 __sys_getsockname+0x8c/0x100
Allocated by task 95: sock_alloc_inode+0x1e/0x280 sock_alloc+0x3d/0x240 __sock_create+0x7e/0x430 smc_create+0x121/0x240
Freed by task 0: kmem_cache_free+0xcc/0x340 rcu_core+0x50a/0x1850
Last potentially related work creation: evict+0x446/0x6c0 smc_clcsock_release+0xa8/0xd0 smc_close_active_abort+0x26a/0x3a0 __smc_lgr_terminate.part.0+0x137/0x2e0
Hold clcsock_release_lock across the pointer check and the getname() callback to serialize with smc_clcsock_release(). Return -EBADF if the CLC socket has already been released, preserving the existing peer state check and the callback's return value otherwise.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel networking subsystem for SMC (Shared Memory Communications) contains a concurrency vulnerability within the smc_getname function that leads to either a use-after-free or a NULL pointer dereference condition. This flaw arises from an improper synchronization mechanism when accessing the CLC socket associated with an SMC socket structure. Specifically, the code path in smc_getname attempts to read and utilize the clcsock pointer without holding the necessary serialization lock known as clcsock_release_lock. In concurrent execution scenarios, particularly during link-group termination processes initiated by functions such as smc_close_active_abort, the CLC socket can be released asynchronously while the parent SMC socket remains open or in a state where getsockname operations are still permissible, such as after a shutdown with SHUT_WR flags.
The operational impact of this vulnerability is significant because it allows an attacker to trigger kernel memory corruption through standard system calls. When a user-space application invokes getsockname on the affected SMC socket, the kernel loads the smc->clcsock pointer into a register or local variable. If the termination worker thread clears this pointer and subsequently frees the underlying sock structure via sock_release before the caller accesses clcsock->ops or executes the getname callback, the system encounters a use-after-free condition. Alternatively, if the pointer is cleared prior to the initial load operation within smc_getname, the kernel attempts to dereference a NULL address, resulting in an immediate crash or denial of service. Although the file reference held by the syscall ensures that the SMC socket itself remains alive and prevents its premature deallocation, this protection does not extend to the internal CLC socket component, leaving it vulnerable to race conditions during asynchronous cleanup routines.
From a vulnerability classification perspective, this issue aligns with CWE-416, Use After Free, as well as CWE-476, NULL Pointer Dereference, depending on the precise timing of the race condition relative to pointer loading and dereferencing. In terms of attack vectors, this represents an exploitation scenario consistent with ATT&CK technique T1059, Command and Scripting Interpreter, where local privilege escalation or system instability is achieved through crafted syscalls that exploit kernel-level concurrency flaws. The vulnerability highlights a critical gap in reference counting and locking strategies within the SMC implementation, specifically regarding the lifecycle management of nested socket structures during teardown sequences.
The resolution involves modifying the smc_getname function to acquire clcsock_release_lock before checking the validity of the clcsock pointer and continuing into the getname callback execution path. This ensures that any concurrent attempt by the termination worker to release the CLC socket is serialized, preventing the window where the pointer could be invalidated between check and use. If the lock acquisition reveals that the CLC socket has already been released during the critical section, the function returns -EBADF to indicate a bad file descriptor state, thereby preserving existing peer state checks while avoiding illegal memory access. This fix effectively closes the race condition by ensuring atomicity in pointer validation against asynchronous release operations managed by rcu_core and related cleanup tasks.