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net, sk_msg: Annotate lockless access to sk_prot on clone 

sk_msg and ULP frameworks override protocol callbacks pointer in
sk->sk_prot, while tcp accesses it locklessly when cloning the listening
socket, that is with neither sk_lock nor sk_callback_lock held.

Once we enable use of listening sockets with sockmap (and hence sk_msg),
there will be shared access to sk->sk_prot if socket is getting cloned
while being inserted/deleted to/from the sockmap from another CPU:

Read side:

tcp_v4_rcv
  sk = __inet_lookup_skb(...)
  tcp_check_req(sk)
    inet_csk(sk)->icsk_af_ops->syn_recv_sock
      tcp_v4_syn_recv_sock
        tcp_create_openreq_child
          inet_csk_clone_lock
            sk_clone_lock
              READ_ONCE(sk->sk_prot)

Write side:

sock_map_ops->map_update_elem
  sock_map_update_elem
    sock_map_update_common
      sock_map_link_no_progs
        tcp_bpf_init
          tcp_bpf_update_sk_prot
            sk_psock_update_proto
              WRITE_ONCE(sk->sk_prot, ops)

sock_map_ops->map_delete_elem
  sock_map_delete_elem
    __sock_map_delete
     sock_map_unref
       sk_psock_put
         sk_psock_drop
           sk_psock_restore_proto
             tcp_update_ulp
               WRITE_ONCE(sk->sk_prot, proto)

Mark the shared access with READ_ONCE/WRITE_ONCE annotations.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200218171023.844439-2-jakub@cloudflare.com
This commit is contained in:
Jakub Sitnicki 2020-02-18 17:10:13 +00:00 committed by Daniel Borkmann
parent e42da4c62a
commit b8e202d1d1
5 changed files with 14 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/skmsg.h
View File

@ -352,7 +352,8 @@ static inline void sk_psock_update_proto(struct sock *sk,
psock->saved_write_space = sk->sk_write_space;
psock->sk_proto = sk->sk_prot;
sk->sk_prot = ops;
/* Pairs with lockless read in sk_clone_lock() */
WRITE_ONCE(sk->sk_prot, ops);
}
static inline void sk_psock_restore_proto(struct sock *sk,

8
net/core/sock.c
View File

@ -1572,13 +1572,14 @@ static inline void sock_lock_init(struct sock *sk)
*/
static void sock_copy(struct sock *nsk, const struct sock *osk)
{
const struct proto *prot = READ_ONCE(osk->sk_prot);
#ifdef CONFIG_SECURITY_NETWORK
void *sptr = nsk->sk_security;
#endif
memcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));
memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
osk->sk_prot->obj_size - offsetof(struct sock, sk_dontcopy_end));
prot->obj_size - offsetof(struct sock, sk_dontcopy_end));
#ifdef CONFIG_SECURITY_NETWORK
nsk->sk_security = sptr;
@ -1792,16 +1793,17 @@ static void sk_init_common(struct sock *sk)
*/
struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
{
struct proto *prot = READ_ONCE(sk->sk_prot);
struct sock *newsk;
bool is_charged = true;
newsk = sk_prot_alloc(sk->sk_prot, priority, sk->sk_family);
newsk = sk_prot_alloc(prot, priority, sk->sk_family);
if (newsk != NULL) {
struct sk_filter *filter;
sock_copy(newsk, sk);
newsk->sk_prot_creator = sk->sk_prot;
newsk->sk_prot_creator = prot;
/* SANITY */
if (likely(newsk->sk_net_refcnt))

4
net/ipv4/tcp_bpf.c
View File

@ -645,8 +645,10 @@ static void tcp_bpf_reinit_sk_prot(struct sock *sk, struct sk_psock *psock)
/* Reinit occurs when program types change e.g. TCP_BPF_TX is removed
* or added requiring sk_prot hook updates. We keep original saved
* hooks in this case.
*
* Pairs with lockless read in sk_clone_lock().
*/
sk->sk_prot = &tcp_bpf_prots[family][config];
WRITE_ONCE(sk->sk_prot, &tcp_bpf_prots[family][config]);
}
static int tcp_bpf_assert_proto_ops(struct proto *ops)

3
net/ipv4/tcp_ulp.c
View File

@ -106,7 +106,8 @@ void tcp_update_ulp(struct sock *sk, struct proto *proto,
if (!icsk->icsk_ulp_ops) {
sk->sk_write_space = write_space;
sk->sk_prot = proto;
/* Pairs with lockless read in sk_clone_lock() */
WRITE_ONCE(sk->sk_prot, proto);
return;
}

3
net/tls/tls_main.c
View File

@ -742,7 +742,8 @@ static void tls_update(struct sock *sk, struct proto *p,
ctx->sk_write_space = write_space;
ctx->sk_proto = p;
} else {
sk->sk_prot = p;
/* Pairs with lockless read in sk_clone_lock(). */
WRITE_ONCE(sk->sk_prot, p);
sk->sk_write_space = write_space;
}
}