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

nfsd: gate nfs3 setacl by argp->mask

nfsd3_proc_setacl() calls set_posix_acl() unconditionally for both
ACL_TYPE_ACCESS and ACL_TYPE_DEFAULT, passing argp->acl_access and
argp->acl_default verbatim. The NFSv3 ACL decoder only populates
those pointers when the corresponding mask bit is set:

    nfs3svc_decode_setaclargs()
      if (args->mask & NFS_ACL)    decode into acl_access
      if (args->mask & NFS_DFACL)  decode into acl_default
      /* otherwise the pointer stays NULL (pc_argzero) */

    nfsd3_proc_setacl()
      set_posix_acl(.., ACL_TYPE_ACCESS,  argp->acl_access)
      set_posix_acl(.., ACL_TYPE_DEFAULT, argp->acl_default)

set_posix_acl(idmap, dentry, type, NULL) is the VFS "remove this
ACL type" operation. A NULL pointer that means "the client did not
send this arm" is therefore indistinguishable from "the client
asked to remove this ACL". A SETACL with mask=NFS_ACL silently
drops the directory's default ACL; mask=0 drops both.

The sibling nfsd3_proc_getacl() already consults argp->mask before
touching each arm; mirror that in setacl.

Fix by wrapping each set_posix_acl() call in the matching mask bit
check and initializing error to 0 before inode_lock so that a
request with neither bit set leaves the on-disk ACLs untouched and
returns nfs_ok. The out_drop_lock path and the unconditional
posix_acl_release() at out: are preserved; both NULL-tolerate the
skipped arms.