In the Linux kernel, the following vulnerability has been resolved: NFS/localio: fix ref leak on...

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

NFS/localio: fix ref leak on nfs_uuid_add_file failure

When nfs_uuid_add_file() races with nfs_uuid_put() tearing down uuid->net, it returns -ENXIO without publishing nfl->nfs_uuid via rcu_assign_pointer(). nfs_open_local_fh() then enters its error branch and only releases the slot's file ref and its paired net ref plus its own entry-time net ref, while the close path is a no-op:

nfs_close_local_fh()
  nfs_uuid = rcu_dereference(nfl->nfs_uuid);
  if (!nfs_uuid) { rcu_read_unlock(); return; }  /* always */

nfsd_open_local_fh() returns localio holding a caller-owned +1 nfsd_file reference (from nfsd_file_get() after nfsd_file_acquire_local()) and an entry-time nfsd_net reference (from its first nfsd_net_try_get()) embedded as nf->nf_net. Both are leaked on the failure path, pinning one nfsd_file (and the underlying struct file, dentry, inode) and one nfsd_net_ref per occurrence, which blocks nfsd_net and netns teardown.

Fix by releasing the caller-owned file ref and its net ref through the existing helper, using a stack-local RCU pointer so the helper can xchg it out, then returning -ENXIO so callers do not dereference a localio whose slot has been cleared:

struct nfsd_file __rcu *tmp = RCU_INITIALIZER(localio);

nfs_to_nfsd_file_put_local(pnf);
nfs_to_nfsd_file_put_local(&tmp);
localio = ERR_PTR(-ENXIO);

The trailing nfs_to_nfsd_net_put(net) continues to release the outer net ref, so all three nfsd_net_try_get() increments are balanced on the error branch.