Linux: net/smc: protect clcsock lifetime in smc_getname

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.