From: Lorenz Bauer <lmb@isovalent.com>
To: "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
David Ahern <dsahern@kernel.org>,
Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Joe Stringer <joe@wand.net.nz>,
Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Hemanth Malla <hemanthmalla@gmail.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
Lorenz Bauer <lmb@isovalent.com>, Joe Stringer <joe@cilium.io>
Subject: [PATCH bpf-next v6 2/8] bpf: reject unhashed sockets in bpf_sk_assign
Date: Thu, 20 Jul 2023 17:30:06 +0200 [thread overview]
Message-ID: <20230720-so-reuseport-v6-2-7021b683cdae@isovalent.com> (raw)
In-Reply-To: <20230720-so-reuseport-v6-0-7021b683cdae@isovalent.com>
The semantics for bpf_sk_assign are as follows:
sk = some_lookup_func()
bpf_sk_assign(skb, sk)
bpf_sk_release(sk)
That is, the sk is not consumed by bpf_sk_assign. The function
therefore needs to make sure that sk lives long enough to be
consumed from __inet_lookup_skb. The path through the stack for a
TCPv4 packet is roughly:
netif_receive_skb_core: takes RCU read lock
__netif_receive_skb_core:
sch_handle_ingress:
tcf_classify:
bpf_sk_assign()
deliver_ptype_list_skb:
deliver_skb:
ip_packet_type->func == ip_rcv:
ip_rcv_core:
ip_rcv_finish_core:
dst_input:
ip_local_deliver:
ip_local_deliver_finish:
ip_protocol_deliver_rcu:
tcp_v4_rcv:
__inet_lookup_skb:
skb_steal_sock
The existing helper takes advantage of the fact that everything
happens in the same RCU critical section: for sockets with
SOCK_RCU_FREE set bpf_sk_assign never takes a reference.
skb_steal_sock then checks SOCK_RCU_FREE again and does sock_put
if necessary.
This approach assumes that SOCK_RCU_FREE is never set on a sk
between bpf_sk_assign and skb_steal_sock, but this invariant is
violated by unhashed UDP sockets. A new UDP socket is created
in TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is only
added in udp_lib_get_port() which happens when a socket is bound.
When bpf_sk_assign was added it wasn't possible to access unhashed
UDP sockets from BPF, so this wasn't a problem. This changed
in commit 0c48eefae712 ("sock_map: Lift socket state restriction
for datagram sockets"), but the helper wasn't adjusted accordingly.
The following sequence of events will therefore lead to a refcount
leak:
1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap.
2. Pull socket out of sockmap and bpf_sk_assign it. Since
SOCK_RCU_FREE is not set we increment the refcount.
3. bind() or connect() the socket, setting SOCK_RCU_FREE.
4. skb_steal_sock will now set refcounted = false due to
SOCK_RCU_FREE.
5. tcp_v4_rcv() skips sock_put().
Fix the problem by rejecting unhashed sockets in bpf_sk_assign().
This matches the behaviour of __inet_lookup_skb which is ultimately
the goal of bpf_sk_assign().
Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Cc: Joe Stringer <joe@cilium.io>
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
net/core/filter.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index 797e8f039696..b5b51ef48c5f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7353,6 +7353,8 @@ BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags)
return -ENETUNREACH;
if (unlikely(sk_fullsock(sk) && sk->sk_reuseport))
return -ESOCKTNOSUPPORT;
+ if (sk_unhashed(sk))
+ return -EOPNOTSUPP;
if (sk_is_refcounted(sk) &&
unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
return -ENOENT;
--
2.41.0
next prev parent reply other threads:[~2023-07-20 15:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-20 15:30 [PATCH bpf-next v6 0/8] Add SO_REUSEPORT support for TC bpf_sk_assign Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 1/8] udp: re-score reuseport groups when connected sockets are present Lorenz Bauer
2023-07-20 15:30 ` Lorenz Bauer [this message]
2023-07-20 21:16 ` [PATCH bpf-next v6 2/8] bpf: reject unhashed sockets in bpf_sk_assign Kuniyuki Iwashima
2023-07-24 8:01 ` Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 3/8] net: export inet_lookup_reuseport and inet6_lookup_reuseport Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 4/8] net: remove duplicate reuseport_lookup functions Lorenz Bauer
2023-07-24 22:55 ` Martin KaFai Lau
2023-07-25 0:53 ` Martin KaFai Lau
2023-07-25 21:19 ` Martin KaFai Lau
2023-07-20 15:30 ` [PATCH bpf-next v6 5/8] net: document inet[6]_lookup_reuseport sk_state requirements Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 6/8] net: remove duplicate sk_lookup helpers Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 7/8] bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign Lorenz Bauer
2023-07-20 21:34 ` Kuniyuki Iwashima
2023-08-08 4:22 ` Kumar Kartikeya Dwivedi
2023-08-08 16:35 ` Lorenz Bauer
2023-07-20 15:30 ` [PATCH bpf-next v6 8/8] selftests/bpf: Test that SO_REUSEPORT can be used with sk_assign helper Lorenz Bauer
2023-07-25 0:42 ` Martin KaFai Lau
2023-07-25 21:20 ` [PATCH bpf-next v6 0/8] Add SO_REUSEPORT support for TC bpf_sk_assign patchwork-bot+netdevbpf
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