On 5/17/19 2:21 PM, Martin KaFai Lau wrote:
> The BPF_FUNC_sk_lookup_xxx helpers return RET_PTR_TO_SOCKET_OR_NULL.
> Meaning a fullsock ptr and its fullsock's fields in bpf_sock can be
> accessed, e.g. type, protocol, mark and priority.
> Some new helper, like bpf_sk_storage_get(), also expects
> ARG_PTR_TO_SOCKET is a fullsock.
>
> bpf_sk_lookup() currently calls sk_to_full_sk() before returning.
> However, the ptr returned from sk_to_full_sk() is not guaranteed
> to be a fullsock. For example, it cannot get a fullsock if sk
> is in TCP_TIME_WAIT.
>
> This patch checks for sk_fullsock() before returning. If it is not
> a fullsock, sock_gen_put() is called if needed and then returns NULL.
>
> Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF")
> Cc: Joe Stringer <joe@xxxxxxxxxxxxx>
> Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> ---
> net/core/filter.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 55bfc941d17a..85def5a20aaf 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5337,8 +5337,14 @@ __bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
> struct sock *sk = __bpf_skc_lookup(skb, tuple, len, caller_net,
> ifindex, proto, netns_id, flags);
>
> - if (sk)
> + if (sk) {
> sk = sk_to_full_sk(sk);
> + if (!sk_fullsock(sk)) {
> + if (!sock_flag(sk, SOCK_RCU_FREE))
> + sock_gen_put(sk);
This looks a bit convoluted/weird.
What about telling/asking __bpf_skc_lookup() to not return a non fullsock instead ?
> + return NULL;
> + }
> + }
>
> return sk;
> }
> @@ -5369,8 +5375,14 @@ bpf_sk_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
> struct sock *sk = bpf_skc_lookup(skb, tuple, len, proto, netns_id,
> flags);
>
> - if (sk)
> + if (sk) {
> sk = sk_to_full_sk(sk);
> + if (!sk_fullsock(sk)) {
> + if (!sock_flag(sk, SOCK_RCU_FREE))
> + sock_gen_put(sk);
> + return NULL;
> + }
> + }
>
> return sk;
> }
>
