From 46f8bc92758c6259bcf945e9216098661c1587cd Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Sat, 9 Feb 2019 23:22:20 -0800 Subject: bpf: Add a bpf_sock pointer to __sk_buff and a bpf_sk_fullsock helper In kernel, it is common to check "skb->sk && sk_fullsock(skb->sk)" before accessing the fields in sock. For example, in __netdev_pick_tx: static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb, struct net_device *sb_dev) { /* ... */ struct sock *sk = skb->sk; if (queue_index != new_index && sk && sk_fullsock(sk) && rcu_access_pointer(sk->sk_dst_cache)) sk_tx_queue_set(sk, new_index); /* ... */ return queue_index; } This patch adds a "struct bpf_sock *sk" pointer to the "struct __sk_buff" where a few of the convert_ctx_access() in filter.c has already been accessing the skb->sk sock_common's fields, e.g. sock_ops_convert_ctx_access(). "__sk_buff->sk" is a PTR_TO_SOCK_COMMON_OR_NULL in the verifier. Some of the fileds in "bpf_sock" will not be directly accessible through the "__sk_buff->sk" pointer. It is limited by the new "bpf_sock_common_is_valid_access()". e.g. The existing "type", "protocol", "mark" and "priority" in bpf_sock are not allowed. The newly added "struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)" can be used to get a sk with all accessible fields in "bpf_sock". This helper is added to both cg_skb and sched_(cls|act). int cg_skb_foo(struct __sk_buff *skb) { struct bpf_sock *sk; sk = skb->sk; if (!sk) return 1; sk = bpf_sk_fullsock(sk); if (!sk) return 1; if (sk->family != AF_INET6 || sk->protocol != IPPROTO_TCP) return 1; /* some_traffic_shaping(); */ return 1; } (1) The sk is read only (2) There is no new "struct bpf_sock_common" introduced. (3) Future kernel sock's members could be added to bpf_sock only instead of repeatedly adding at multiple places like currently in bpf_sock_ops_md, bpf_sock_addr_md, sk_reuseport_md...etc. (4) After "sk = skb->sk", the reg holding sk is in type PTR_TO_SOCK_COMMON_OR_NULL. (5) After bpf_sk_fullsock(), the return type will be in type PTR_TO_SOCKET_OR_NULL which is the same as the return type of bpf_sk_lookup_xxx(). However, bpf_sk_fullsock() does not take refcnt. The acquire_reference_state() is only depending on the return type now. To avoid it, a new is_acquire_function() is checked before calling acquire_reference_state(). (6) The WARN_ON in "release_reference_state()" is no longer an internal verifier bug. When reg->id is not found in state->refs[], it means the bpf_prog does something wrong like "bpf_sk_release(bpf_sk_fullsock(skb->sk))" where reference has never been acquired by calling "bpf_sk_fullsock(skb->sk)". A -EINVAL and a verbose are done instead of WARN_ON. A test is added to the test_verifier in a later patch. Since the WARN_ON in "release_reference_state()" is no longer needed, "__release_reference_state()" is folded into "release_reference_state()" also. Acked-by: Alexei Starovoitov Signed-off-by: Martin KaFai Lau Signed-off-by: Alexei Starovoitov --- include/uapi/linux/bpf.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'include/uapi') diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 1777fa0c61e4..5d79cba74ddc 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2329,6 +2329,14 @@ union bpf_attr { * "**y**". * Return * 0 + * + * struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk) + * Description + * This helper gets a **struct bpf_sock** pointer such + * that all the fields in bpf_sock can be accessed. + * Return + * A **struct bpf_sock** pointer on success, or NULL in + * case of failure. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -2425,7 +2433,8 @@ union bpf_attr { FN(msg_pop_data), \ FN(rc_pointer_rel), \ FN(spin_lock), \ - FN(spin_unlock), + FN(spin_unlock), \ + FN(sk_fullsock), /* integer value in 'imm' field of BPF_CALL instruction selects which helper * function eBPF program intends to call @@ -2545,6 +2554,7 @@ struct __sk_buff { __u64 tstamp; __u32 wire_len; __u32 gso_segs; + __bpf_md_ptr(struct bpf_sock *, sk); }; struct bpf_tunnel_key { -- cgit v1.2.3