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Date: Fri, 17 May 2019 14:51:48 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Martin KaFai Lau <kafai@...com>, bpf@...r.kernel.org, netdev@...r.kernel.org Cc: Alexei Starovoitov <ast@...com>, Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com, Joe Stringer <joe@...valent.com> Subject: Re: [PATCH bpf] bpf: Check sk_fullsock() before returning from bpf_sk_lookup() 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@...valent.com> > Signed-off-by: Martin KaFai Lau <kafai@...com> > --- > 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; > } >
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