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authorAndrey Ignatov <rdna@fb.com>2018-03-30 15:08:05 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2018-03-31 02:15:54 +0200
commitd74bad4e74ee373787a9ae24197c17b7cdc428d5 (patch)
tree568fbc1dc8c41b35e442226ca15ef0c16cc2996e /net/ipv4/tcp_ipv4.c
parentnet: Introduce __inet_bind() and __inet6_bind (diff)
downloadlinux-dev-d74bad4e74ee373787a9ae24197c17b7cdc428d5.tar.xz
linux-dev-d74bad4e74ee373787a9ae24197c17b7cdc428d5.zip
bpf: Hooks for sys_connect
== The problem == See description of the problem in the initial patch of this patch set. == The solution == The patch provides much more reliable in-kernel solution for the 2nd part of the problem: making outgoing connecttion from desired IP. It adds new attach types `BPF_CGROUP_INET4_CONNECT` and `BPF_CGROUP_INET6_CONNECT` for program type `BPF_PROG_TYPE_CGROUP_SOCK_ADDR` that can be used to override both source and destination of a connection at connect(2) time. Local end of connection can be bound to desired IP using newly introduced BPF-helper `bpf_bind()`. It allows to bind to only IP though, and doesn't support binding to port, i.e. leverages `IP_BIND_ADDRESS_NO_PORT` socket option. There are two reasons for this: * looking for a free port is expensive and can affect performance significantly; * there is no use-case for port. As for remote end (`struct sockaddr *` passed by user), both parts of it can be overridden, remote IP and remote port. It's useful if an application inside cgroup wants to connect to another application inside same cgroup or to itself, but knows nothing about IP assigned to the cgroup. Support is added for IPv4 and IPv6, for TCP and UDP. IPv4 and IPv6 have separate attach types for same reason as sys_bind hooks, i.e. to prevent reading from / writing to e.g. user_ip6 fields when user passes sockaddr_in since it'd be out-of-bound. == Implementation notes == The patch introduces new field in `struct proto`: `pre_connect` that is a pointer to a function with same signature as `connect` but is called before it. The reason is in some cases BPF hooks should be called way before control is passed to `sk->sk_prot->connect`. Specifically `inet_dgram_connect` autobinds socket before calling `sk->sk_prot->connect` and there is no way to call `bpf_bind()` from hooks from e.g. `ip4_datagram_connect` or `ip6_datagram_connect` since it'd cause double-bind. On the other hand `proto.pre_connect` provides a flexible way to add BPF hooks for connect only for necessary `proto` and call them at desired time before `connect`. Since `bpf_bind()` is allowed to bind only to IP and autobind in `inet_dgram_connect` binds only port there is no chance of double-bind. bpf_bind() sets `force_bind_address_no_port` to bind to only IP despite of value of `bind_address_no_port` socket field. bpf_bind() sets `with_lock` to `false` when calling to __inet_bind() and __inet6_bind() since all call-sites, where bpf_bind() is called, already hold socket lock. Signed-off-by: Andrey Ignatov <rdna@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'net/ipv4/tcp_ipv4.c')
-rw-r--r--net/ipv4/tcp_ipv4.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2c6aec2643e8..3c11d992d784 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -140,6 +140,21 @@ int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
}
EXPORT_SYMBOL_GPL(tcp_twsk_unique);
+static int tcp_v4_pre_connect(struct sock *sk, struct sockaddr *uaddr,
+ int addr_len)
+{
+ /* This check is replicated from tcp_v4_connect() and intended to
+ * prevent BPF program called below from accessing bytes that are out
+ * of the bound specified by user in addr_len.
+ */
+ if (addr_len < sizeof(struct sockaddr_in))
+ return -EINVAL;
+
+ sock_owned_by_me(sk);
+
+ return BPF_CGROUP_RUN_PROG_INET4_CONNECT(sk, uaddr);
+}
+
/* This will initiate an outgoing connection. */
int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
@@ -2409,6 +2424,7 @@ struct proto tcp_prot = {
.name = "TCP",
.owner = THIS_MODULE,
.close = tcp_close,
+ .pre_connect = tcp_v4_pre_connect,
.connect = tcp_v4_connect,
.disconnect = tcp_disconnect,
.accept = inet_csk_accept,