Re: [PATCH net v3] net/smc: protect clcsock lifetime in smc_getname

[Dust Li]

On 2026-10-08 16:44:44, Chengfeng Ye wrote:
>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.
>
>Fixes: b03faa1fafc8 ("net/smc: postpone release of clcsock")
>Cc: stable@xxxxxxxxxxxxxxx
>Assisted-by: GPT-6.1-Sol
>Signed-off-by: Chengfeng Ye <nicoyip.dev@xxxxxxxxx>
>---
>Changes in v3:
>- Limit the fix to smc_getname(), as requested by Mahanta. The code
>  change is identical to v1 and uses the existing release mutex.
>- Drop the new clcsock_lock and the other v2 changes. Mahanta will
>  address the other readers through the broader CLC lifetime changes
>  discussed with Dust Li.
>- Rebase onto current net/main; keep the stable Cc.

Agree on the current fix.

Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>

Best regards,
Dust