CVE-2025-68366

In the Linux kernel, the following vulnerability has been resolved:

nbd: defer config unlock in nbdgenlconnect

There is one use-after-free warning when running NBDCMDCONNECT and NBDCLEARSOCK:

nbdgenlconnect nbdallocandinitconfig // configrefs=1 nbdstartdevice // configrefs=2 set NBDRTHASCONFIGREF open nbd // configrefs=3 recvwork done // configrefs=2 NBDCLEARSOCK // configrefs=1 close nbd // configrefs=0 refcountinc -> uaf

------------[ cut here ]------------ refcountt: addition on 0; use-after-free. WARNING: CPU: 24 PID: 1014 at lib/refcount.c:25 refcountwarnsaturate+0x12e/0x290 nbdgenlconnect+0x16d0/0x1ab0 genlfamilyrcvmsgdoit+0x1f3/0x310 genlrcv_msg+0x44a/0x790

The issue can be easily reproduced by adding a small delay before refcountinc(&nbd->configrefs) in nbdgenlconnect():

    mutex_unlock(&nbd->config_lock);
    if (!ret) {
            set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);

+ printk("before sleep\n"); + mdelay(5 * 1000); + printk("after sleep\n"); refcountinc(&nbd->configrefs); nbdconnectreply(info, nbd->index); }