On 04/24/2019 11:31 PM, Stanislav Fomichev wrote:
> target_fd is target namespace. If there is a flow dissector BPF program
> attached to that namespace, its (single) id is returned.
>
> v4:
> * add missing put_net (Jann Horn)
>
> v3:
> * add missing inline to skb_flow_dissector_prog_query static def
> (kbuild test robot <lkp@xxxxxxxxx>)
>
> v2:
> * don't sleep in rcu critical section (Jakub Kicinski)
> * check input prog_cnt (exit early)
>
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
> include/linux/skbuff.h | 8 +++++++
> kernel/bpf/syscall.c | 2 ++
> net/core/flow_dissector.c | 46 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 56 insertions(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 998256c2820b..6d58fa8a65fd 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1258,11 +1258,19 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
> unsigned int key_count);
>
> #ifdef CONFIG_NET
> +int skb_flow_dissector_prog_query(const union bpf_attr *attr,
> + union bpf_attr __user *uattr);
> int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
> struct bpf_prog *prog);
>
> int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr);
> #else
> +static inline int skb_flow_dissector_prog_query(const union bpf_attr *attr,
> + union bpf_attr __user *uattr)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> static inline int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
> struct bpf_prog *prog)
> {
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 92c9b8a32b50..b0de49598341 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2009,6 +2009,8 @@ static int bpf_prog_query(const union bpf_attr *attr,
> break;
> case BPF_LIRC_MODE2:
> return lirc_prog_query(attr, uattr);
> + case BPF_FLOW_DISSECTOR:
> + return skb_flow_dissector_prog_query(attr, uattr);
> default:
> return -EINVAL;
> }
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index fac712cee9d5..27466e54ad3a 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -65,6 +65,52 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
> }
> EXPORT_SYMBOL(skb_flow_dissector_init);
>
> +int skb_flow_dissector_prog_query(const union bpf_attr *attr,
> + union bpf_attr __user *uattr)
> +{
> + __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
> + u32 prog_id, prog_cnt = 0, flags = 0;
> + struct bpf_prog *attached;
> + struct net *net;
> + int ret = 0;
> +
> + if (attr->query.query_flags)
> + return -EINVAL;
> +
> + net = get_net_ns_by_fd(attr->query.target_fd);
> + if (IS_ERR(net))
> + return PTR_ERR(net);
> +
> + rcu_read_lock();
> + attached = rcu_dereference(net->flow_dissector_prog);
> + if (attached) {
> + prog_cnt = 1;
> + prog_id = attached->aux->id;
> + }
> + rcu_read_unlock();
Patch looks good to me, one small nit: is there any reason you didn't
do the put_net(net) right after the rcu_read_unlock() above? Below it's
not really needed anymore, so this would also simplify the error paths
by being able to directly return in error case, no?
> + if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags))) {
> + ret = -EFAULT;
> + goto out;
> + }
> + if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt))) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
> + goto out;
> +
> + if (copy_to_user(prog_ids, &prog_id, sizeof(u32))) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> +out:
> + put_net(net);
> + return ret;
> +}
> +
> int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
> struct bpf_prog *prog)
> {
>
