From d74bad4e74ee373787a9ae24197c17b7cdc428d5 Mon Sep 17 00:00:00 2001 From: Andrey Ignatov Date: Fri, 30 Mar 2018 15:08:05 -0700 Subject: 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 Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- kernel/bpf/syscall.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'kernel/bpf') diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 2cad66a4cacb..cf1b29bc0ab8 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1180,6 +1180,8 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type, switch (expected_attach_type) { case BPF_CGROUP_INET4_BIND: case BPF_CGROUP_INET6_BIND: + case BPF_CGROUP_INET4_CONNECT: + case BPF_CGROUP_INET6_CONNECT: return 0; default: return -EINVAL; @@ -1491,6 +1493,8 @@ static int bpf_prog_attach(const union bpf_attr *attr) break; case BPF_CGROUP_INET4_BIND: case BPF_CGROUP_INET6_BIND: + case BPF_CGROUP_INET4_CONNECT: + case BPF_CGROUP_INET6_CONNECT: ptype = BPF_PROG_TYPE_CGROUP_SOCK_ADDR; break; case BPF_CGROUP_SOCK_OPS: @@ -1557,6 +1561,8 @@ static int bpf_prog_detach(const union bpf_attr *attr) break; case BPF_CGROUP_INET4_BIND: case BPF_CGROUP_INET6_BIND: + case BPF_CGROUP_INET4_CONNECT: + case BPF_CGROUP_INET6_CONNECT: ptype = BPF_PROG_TYPE_CGROUP_SOCK_ADDR; break; case BPF_CGROUP_SOCK_OPS: @@ -1610,6 +1616,8 @@ static int bpf_prog_query(const union bpf_attr *attr, case BPF_CGROUP_INET_SOCK_CREATE: case BPF_CGROUP_INET4_BIND: case BPF_CGROUP_INET6_BIND: + case BPF_CGROUP_INET4_CONNECT: + case BPF_CGROUP_INET6_CONNECT: case BPF_CGROUP_SOCK_OPS: case BPF_CGROUP_DEVICE: break; -- cgit v1.2.3