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Wed, 25 Mar 2020 13:47:06 -0700 (PDT) MIME-Version: 1.0 References: <20200325055745.10710-1-joe@wand.net.nz> <20200325055745.10710-5-joe@wand.net.nz> In-Reply-To: From: Joe Stringer Date: Wed, 25 Mar 2020 13:46:43 -0700 Message-ID: Subject: Re: [PATCHv2 bpf-next 4/5] bpf: Don't refcount LISTEN sockets in sk_assign() To: Lorenz Bauer Cc: Joe Stringer , bpf , Networking , Daniel Borkmann , Alexei Starovoitov , Eric Dumazet , Martin Lau Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Mar 25, 2020 at 3:29 AM Lorenz Bauer wrote: > > On Wed, 25 Mar 2020 at 05:58, Joe Stringer wrote: > > > > Avoid taking a reference on listen sockets by checking the socket type > > in the sk_assign and in the corresponding skb_steal_sock() code in the > > the transport layer, and by ensuring that the prefetch free (sock_pfree) > > function uses the same logic to check whether the socket is refcounted. > > > > Suggested-by: Martin KaFai Lau > > Signed-off-by: Joe Stringer > > --- > > v2: Initial version > > --- > > include/net/sock.h | 25 +++++++++++++++++-------- > > net/core/filter.c | 6 +++--- > > net/core/sock.c | 3 ++- > > 3 files changed, 22 insertions(+), 12 deletions(-) > > > > diff --git a/include/net/sock.h b/include/net/sock.h > > index 1ca2e808cb8e..3ec1865f173e 100644 > > --- a/include/net/sock.h > > +++ b/include/net/sock.h > > @@ -2533,6 +2533,21 @@ skb_sk_is_prefetched(struct sk_buff *skb) > > return skb->destructor == sock_pfree; > > } > > > > +/* This helper checks if a socket is a full socket, > > + * ie _not_ a timewait or request socket. > > + */ > > +static inline bool sk_fullsock(const struct sock *sk) > > +{ > > + return (1 << sk->sk_state) & ~(TCPF_TIME_WAIT | TCPF_NEW_SYN_RECV); > > +} > > + > > +static inline bool > > +sk_is_refcounted(struct sock *sk) > > +{ > > + /* Only full sockets have sk->sk_flags. */ > > + return !sk_fullsock(sk) || !sock_flag(sk, SOCK_RCU_FREE); > > +} > > + > > /** > > * skb_steal_sock > > * @skb to steal the socket from > > @@ -2545,6 +2560,8 @@ skb_steal_sock(struct sk_buff *skb, bool *refcounted) > > struct sock *sk = skb->sk; > > > > *refcounted = true; > > + if (skb_sk_is_prefetched(skb)) > > + *refcounted = sk_is_refcounted(sk); > > skb->destructor = NULL; > > skb->sk = NULL; > > return sk; > > @@ -2553,14 +2570,6 @@ skb_steal_sock(struct sk_buff *skb, bool *refcounted) > > return NULL; > > } > > > > -/* This helper checks if a socket is a full socket, > > - * ie _not_ a timewait or request socket. > > - */ > > -static inline bool sk_fullsock(const struct sock *sk) > > -{ > > - return (1 << sk->sk_state) & ~(TCPF_TIME_WAIT | TCPF_NEW_SYN_RECV); > > -} > > - > > /* Checks if this SKB belongs to an HW offloaded socket > > * and whether any SW fallbacks are required based on dev. > > * Check decrypted mark in case skb_orphan() cleared socket. > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 0fada7fe9b75..997b8606167e 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -5343,8 +5343,7 @@ static const struct bpf_func_proto bpf_sk_lookup_udp_proto = { > > > > BPF_CALL_1(bpf_sk_release, struct sock *, sk) > > { > > - /* Only full sockets have sk->sk_flags. */ > > - if (!sk_fullsock(sk) || !sock_flag(sk, SOCK_RCU_FREE)) > > + if (sk_is_refcounted(sk)) > > sock_gen_put(sk); > > return 0; > > } > > @@ -5870,7 +5869,8 @@ BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags) > > return -ESOCKTNOSUPPORT; > > if (unlikely(dev_net(skb->dev) != sock_net(sk))) > > return -ENETUNREACH; > > - if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) > > + if (sk_is_refcounted(sk) && > > + unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) > > return -ENOENT; > > > > skb_orphan(skb); > > diff --git a/net/core/sock.c b/net/core/sock.c > > index cfaf60267360..a2ab79446f59 100644 > > --- a/net/core/sock.c > > +++ b/net/core/sock.c > > @@ -2076,7 +2076,8 @@ EXPORT_SYMBOL(sock_efree); > > */ > > void sock_pfree(struct sk_buff *skb) > > { > > - sock_edemux(skb); > > + if (sk_is_refcounted(skb->sk)) > > + sock_edemux(skb); > > sock_edemux calls sock_gen_put, which is also called by > bpf_sk_release. Is it worth teaching sock_gen_put about > sk_fullsock, and dropping the other helpers? I was considering this > when fixing up sk_release, but then forgot > about it. I like the idea, but I'm concerned about breaking things outside the focus of this new helper if the skb_sk_is_prefetched() function from patch 1 is allowed to return true for sockets other than the ones assigned from the bpf_sk_assign() helper. At a glance there's users of sock_efree (which sock_edemux can be defined to) like netem_enqueue() which may inadvertently trigger unexpected paths here. I think it's more explicit so more obviously correct if the destructor pointer used in this series is unique compared to other paths, even if the underlying code is the same.