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Date: Tue, 13 Aug 2019 16:58:36 +0000
From: Yonghong Song <yhs@...com>
To: Stanislav Fomichev <sdf@...gle.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC: "davem@...emloft.net" <davem@...emloft.net>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
Martin Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3 2/4] bpf: support cloning sk storage on
accept()
On 8/13/19 9:26 AM, Stanislav Fomichev wrote:
> Add new helper bpf_sk_storage_clone which optionally clones sk storage
> and call it from sk_clone_lock.
>
> Cc: Martin KaFai Lau <kafai@...com>
> Cc: Yonghong Song <yhs@...com>
> Acked-by: Yonghong Song <yhs@...com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> include/net/bpf_sk_storage.h | 10 ++++
> include/uapi/linux/bpf.h | 3 +
> net/core/bpf_sk_storage.c | 103 ++++++++++++++++++++++++++++++++++-
> net/core/sock.c | 9 ++-
> 4 files changed, 119 insertions(+), 6 deletions(-)
>
> diff --git a/include/net/bpf_sk_storage.h b/include/net/bpf_sk_storage.h
> index b9dcb02e756b..8e4f831d2e52 100644
> --- a/include/net/bpf_sk_storage.h
> +++ b/include/net/bpf_sk_storage.h
> @@ -10,4 +10,14 @@ void bpf_sk_storage_free(struct sock *sk);
> extern const struct bpf_func_proto bpf_sk_storage_get_proto;
> extern const struct bpf_func_proto bpf_sk_storage_delete_proto;
>
> +#ifdef CONFIG_BPF_SYSCALL
> +int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk);
> +#else
> +static inline int bpf_sk_storage_clone(const struct sock *sk,
> + struct sock *newsk)
> +{
> + return 0;
> +}
> +#endif
> +
> #endif /* _BPF_SK_STORAGE_H */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4393bd4b2419..0ef594ac3899 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -337,6 +337,9 @@ enum bpf_attach_type {
> #define BPF_F_RDONLY_PROG (1U << 7)
> #define BPF_F_WRONLY_PROG (1U << 8)
>
> +/* Clone map from listener for newly accepted socket */
> +#define BPF_F_CLONE (1U << 9)
> +
> /* flags for BPF_PROG_QUERY */
> #define BPF_F_QUERY_EFFECTIVE (1U << 0)
>
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 94c7f77ecb6b..1bc7de7e18ba 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -12,6 +12,9 @@
>
> static atomic_t cache_idx;
>
> +#define SK_STORAGE_CREATE_FLAG_MASK \
> + (BPF_F_NO_PREALLOC | BPF_F_CLONE)
> +
> struct bucket {
> struct hlist_head list;
> raw_spinlock_t lock;
> @@ -209,7 +212,6 @@ static void selem_unlink_sk(struct bpf_sk_storage_elem *selem)
> kfree_rcu(sk_storage, rcu);
> }
>
> -/* sk_storage->lock must be held and sk_storage->list cannot be empty */
> static void __selem_link_sk(struct bpf_sk_storage *sk_storage,
> struct bpf_sk_storage_elem *selem)
> {
> @@ -509,7 +511,7 @@ static int sk_storage_delete(struct sock *sk, struct bpf_map *map)
> return 0;
> }
>
> -/* Called by __sk_destruct() */
> +/* Called by __sk_destruct() & bpf_sk_storage_clone() */
> void bpf_sk_storage_free(struct sock *sk)
> {
> struct bpf_sk_storage_elem *selem;
> @@ -557,6 +559,11 @@ static void bpf_sk_storage_map_free(struct bpf_map *map)
>
> smap = (struct bpf_sk_storage_map *)map;
>
> + /* Note that this map might be concurrently cloned from
> + * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
> + * RCU read section to finish before proceeding. New RCU
> + * read sections should be prevented via bpf_map_inc_not_zero.
> + */
> synchronize_rcu();
>
> /* bpf prog and the userspace can no longer access this map
> @@ -601,7 +608,9 @@ static void bpf_sk_storage_map_free(struct bpf_map *map)
>
> static int bpf_sk_storage_map_alloc_check(union bpf_attr *attr)
> {
> - if (attr->map_flags != BPF_F_NO_PREALLOC || attr->max_entries ||
> + if (attr->map_flags & ~SK_STORAGE_CREATE_FLAG_MASK ||
> + !(attr->map_flags & BPF_F_NO_PREALLOC) ||
> + attr->max_entries ||
> attr->key_size != sizeof(int) || !attr->value_size ||
> /* Enforce BTF for userspace sk dumping */
> !attr->btf_key_type_id || !attr->btf_value_type_id)
> @@ -739,6 +748,94 @@ static int bpf_fd_sk_storage_delete_elem(struct bpf_map *map, void *key)
> return err;
> }
>
> +static struct bpf_sk_storage_elem *
> +bpf_sk_storage_clone_elem(struct sock *newsk,
> + struct bpf_sk_storage_map *smap,
> + struct bpf_sk_storage_elem *selem)
> +{
> + struct bpf_sk_storage_elem *copy_selem;
> +
> + copy_selem = selem_alloc(smap, newsk, NULL, true);
> + if (!copy_selem)
> + return NULL;
> +
> + if (map_value_has_spin_lock(&smap->map))
> + copy_map_value_locked(&smap->map, SDATA(copy_selem)->data,
> + SDATA(selem)->data, true);
> + else
> + copy_map_value(&smap->map, SDATA(copy_selem)->data,
> + SDATA(selem)->data);
> +
> + return copy_selem;
> +}
> +
> +int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
> +{
> + struct bpf_sk_storage *new_sk_storage = NULL;
> + struct bpf_sk_storage *sk_storage;
> + struct bpf_sk_storage_elem *selem;
> + int ret;
> +
> + RCU_INIT_POINTER(newsk->sk_bpf_storage, NULL);
> +
> + rcu_read_lock();
> + sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +
> + if (!sk_storage || hlist_empty(&sk_storage->list))
> + goto out;
> +
> + hlist_for_each_entry_rcu(selem, &sk_storage->list, snode) {
> + struct bpf_sk_storage_elem *copy_selem;
> + struct bpf_sk_storage_map *smap;
> + struct bpf_map *map;
> +
> + smap = rcu_dereference(SDATA(selem)->smap);
> + if (!(smap->map.map_flags & BPF_F_CLONE))
> + continue;
> +
> + map = bpf_map_inc_not_zero(&smap->map, false);
> + if (IS_ERR(map))
> + continue;
> +
> + copy_selem = bpf_sk_storage_clone_elem(newsk, smap, selem);
> + if (!copy_selem) {
> + ret = -ENOMEM;
> + bpf_map_put(map);
> + goto err;
> + }
> +
> + if (new_sk_storage) {
> + selem_link_map(smap, copy_selem);
> + __selem_link_sk(new_sk_storage, copy_selem);
> + } else {
> + ret = sk_storage_alloc(newsk, smap, copy_selem);
> + if (ret) {
> + kfree(copy_selem);
> + atomic_sub(smap->elem_size,
> + &newsk->sk_omem_alloc);
> + bpf_map_put(map);
> + goto err;
> + }
> +
> + new_sk_storage = rcu_dereference(copy_selem->sk_storage);
> + }
> + bpf_map_put(map);
> + }
> +
> +out:
> + rcu_read_unlock();
> + return 0;
> +
> +err:
> + rcu_read_unlock();
> +
> + /* Don't free anything explicitly here, caller is responsible to
> + * call bpf_sk_storage_free in case of an error.
> + */
> +
> + return ret;
A nit.
If you set ret = 0 initially, you do not need the above two
rcu_read_unlock(). One "return ret" should be enough.
The comment can be changed to
/* In case of an error, ... */
> +}
> +
> BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
> void *, value, u64, flags)
> {
> diff --git a/net/core/sock.c b/net/core/sock.c
> index d57b0cc995a0..f5e801a9cea4 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1851,9 +1851,12 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> goto out;
> }
> RCU_INIT_POINTER(newsk->sk_reuseport_cb, NULL);
> -#ifdef CONFIG_BPF_SYSCALL
> - RCU_INIT_POINTER(newsk->sk_bpf_storage, NULL);
> -#endif
> +
> + if (bpf_sk_storage_clone(sk, newsk)) {
> + sk_free_unlock_clone(newsk);
> + newsk = NULL;
> + goto out;
> + }
>
> newsk->sk_err = 0;
> newsk->sk_err_soft = 0;
>
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