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Date: Thu, 8 Aug 2019 06:39:49 +0000
From: Martin Lau <kafai@...com>
To: Stanislav Fomichev <sdf@...gle.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"davem@...emloft.net" <davem@...emloft.net>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 1/3] bpf: support cloning sk storage on accept()
On Wed, Aug 07, 2019 at 08:47:18AM -0700, Stanislav Fomichev wrote:
> Add new helper bpf_sk_storage_clone which optionally clones sk storage
> and call it from bpf_sk_storage_clone. Reuse the gap in
> bpf_sk_storage_elem to store clone/non-clone flag.
>
> Cc: Martin KaFai Lau <kafai@...com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> include/net/bpf_sk_storage.h | 10 ++++
> include/uapi/linux/bpf.h | 1 +
> net/core/bpf_sk_storage.c | 102 +++++++++++++++++++++++++++++++++--
> net/core/sock.c | 9 ++--
> 4 files changed, 115 insertions(+), 7 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..00459ca4c8cf 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2931,6 +2931,7 @@ enum bpf_func_id {
>
> /* BPF_FUNC_sk_storage_get flags */
> #define BPF_SK_STORAGE_GET_F_CREATE (1ULL << 0)
> +#define BPF_SK_STORAGE_GET_F_CLONE (1ULL << 1)
It is only used in bpf_sk_storage_get().
What if the elem is created from bpf_fd_sk_storage_update_elem()
i.e. from the syscall API ?
What may be the use case for a map to have both CLONE and non-CLONE
elements? If it is not the case, would it be better to add
BPF_F_CLONE to bpf_attr->map_flags?
>
> /* Mode for BPF_FUNC_skb_adjust_room helper. */
> enum bpf_adj_room_mode {
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 94c7f77ecb6b..b6dea67965bc 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 BPF_SK_STORAGE_GET_F_MASK (BPF_SK_STORAGE_GET_F_CREATE | \
> + BPF_SK_STORAGE_GET_F_CLONE)
> +
> struct bucket {
> struct hlist_head list;
> raw_spinlock_t lock;
> @@ -66,7 +69,8 @@ struct bpf_sk_storage_elem {
> struct hlist_node snode; /* Linked to bpf_sk_storage */
> struct bpf_sk_storage __rcu *sk_storage;
> struct rcu_head rcu;
> - /* 8 bytes hole */
> + u8 clone:1;
> + /* 7 bytes hole */
> /* The data is stored in aother cacheline to minimize
> * the number of cachelines access during a cache hit.
> */
> @@ -509,7 +513,7 @@ 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;
> @@ -739,19 +743,106 @@ 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 ERR_PTR(-ENOMEM);
nit.
may be just return NULL as selem_alloc() does.
> +
> + 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_map *smap;
> + struct bpf_sk_storage_elem *copy_selem;
> +
> + if (!selem->clone)
> + continue;
> +
> + smap = rcu_dereference(SDATA(selem)->smap);
> + if (!smap)
smap should not be NULL.
> + continue;
> +
> + copy_selem = bpf_sk_storage_clone_elem(newsk, smap, selem);
> + if (IS_ERR(copy_selem)) {
> + ret = PTR_ERR(copy_selem);
> + goto err;
> + }
> +
> + if (!new_sk_storage) {
> + ret = sk_storage_alloc(newsk, smap, copy_selem);
> + if (ret) {
> + kfree(copy_selem);
> + atomic_sub(smap->elem_size,
> + &newsk->sk_omem_alloc);
> + goto err;
> + }
> +
> + new_sk_storage = rcu_dereference(copy_selem->sk_storage);
> + continue;
> + }
> +
> + raw_spin_lock_bh(&new_sk_storage->lock);
> + selem_link_map(smap, copy_selem);
Unlike the existing selem-update use-cases in bpf_sk_storage.c,
the smap->map.refcnt has not been held here. Reading the smap
is fine. However, adding a new selem to a deleting smap is an issue.
Hence, I think bpf_map_inc_not_zero() should be done first.
> + __selem_link_sk(new_sk_storage, copy_selem);
> + raw_spin_unlock_bh(&new_sk_storage->lock);
> + }
> +
> +out:
> + rcu_read_unlock();
> + return 0;
> +
> +err:
> + rcu_read_unlock();
> +
> + bpf_sk_storage_free(newsk);
> + return ret;
> +}
> +
> BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
> void *, value, u64, flags)
> {
> struct bpf_sk_storage_data *sdata;
>
> - if (flags > BPF_SK_STORAGE_GET_F_CREATE)
> + if (flags & ~BPF_SK_STORAGE_GET_F_MASK)
> + return (unsigned long)NULL;
> +
> + if ((flags & BPF_SK_STORAGE_GET_F_CLONE) &&
> + !(flags & BPF_SK_STORAGE_GET_F_CREATE))
> return (unsigned long)NULL;
>
> sdata = sk_storage_lookup(sk, map, true);
> if (sdata)
> return (unsigned long)sdata->data;
>
> - if (flags == BPF_SK_STORAGE_GET_F_CREATE &&
> + if ((flags & BPF_SK_STORAGE_GET_F_CREATE) &&
> /* Cannot add new elem to a going away sk.
> * Otherwise, the new elem may become a leak
> * (and also other memory issues during map
> @@ -762,6 +853,9 @@ BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
> /* sk must be a fullsock (guaranteed by verifier),
> * so sock_gen_put() is unnecessary.
> */
> + if (!IS_ERR(sdata))
> + SELEM(sdata)->clone =
> + !!(flags & BPF_SK_STORAGE_GET_F_CLONE);
> sock_put(sk);
> return IS_ERR(sdata) ?
> (unsigned long)NULL : (unsigned long)sdata->data;
> 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;
> --
> 2.22.0.770.g0f2c4a37fd-goog
>
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