From 1cedee13d25ab118d325f95588c1a084e9317229 Mon Sep 17 00:00:00 2001 From: Andrey Ignatov Date: Fri, 25 May 2018 08:55:23 -0700 Subject: bpf: Hooks for sys_sendmsg In addition to already existing BPF hooks for sys_bind and sys_connect, the patch provides new hooks for sys_sendmsg. It leverages existing BPF program type `BPF_PROG_TYPE_CGROUP_SOCK_ADDR` that provides access to socket itlself (properties like family, type, protocol) and user-passed `struct sockaddr *` so that BPF program can override destination IP and port for system calls such as sendto(2) or sendmsg(2) and/or assign source IP to the socket. The hooks are implemented as two new attach types: `BPF_CGROUP_UDP4_SENDMSG` and `BPF_CGROUP_UDP6_SENDMSG` for UDPv4 and UDPv6 correspondingly. UDPv4 and UDPv6 separate attach types for same reason as sys_bind and sys_connect 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. The difference with already existing hooks is sys_sendmsg are implemented only for unconnected UDP. For TCP it doesn't make sense to change user-provided `struct sockaddr *` at sendto(2)/sendmsg(2) time since socket either was already connected and has source/destination set or wasn't connected and call to sendto(2)/sendmsg(2) would lead to ENOTCONN anyway. Connected UDP is already handled by sys_connect hooks that can override source/destination at connect time and use fast-path later, i.e. these hooks don't affect UDP fast-path. Rewriting source IP is implemented differently than that in sys_connect hooks. When sys_sendmsg is used with unconnected UDP it doesn't work to just bind socket to desired local IP address since source IP can be set on per-packet basis by using ancillary data (cmsg(3)). So no matter if socket is bound or not, source IP has to be rewritten on every call to sys_sendmsg. To do so two new fields are added to UAPI `struct bpf_sock_addr`; * `msg_src_ip4` to set source IPv4 for UDPv4; * `msg_src_ip6` to set source IPv6 for UDPv6. Signed-off-by: Andrey Ignatov Acked-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Signed-off-by: Daniel Borkmann --- net/core/filter.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'net/core/filter.c') diff --git a/net/core/filter.c b/net/core/filter.c index acf1f4fb99d1..24e6ce8be567 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5299,6 +5299,7 @@ static bool sock_addr_is_valid_access(int off, int size, switch (prog->expected_attach_type) { case BPF_CGROUP_INET4_BIND: case BPF_CGROUP_INET4_CONNECT: + case BPF_CGROUP_UDP4_SENDMSG: break; default: return false; @@ -5308,6 +5309,24 @@ static bool sock_addr_is_valid_access(int off, int size, switch (prog->expected_attach_type) { case BPF_CGROUP_INET6_BIND: case BPF_CGROUP_INET6_CONNECT: + case BPF_CGROUP_UDP6_SENDMSG: + break; + default: + return false; + } + break; + case bpf_ctx_range(struct bpf_sock_addr, msg_src_ip4): + switch (prog->expected_attach_type) { + case BPF_CGROUP_UDP4_SENDMSG: + break; + default: + return false; + } + break; + case bpf_ctx_range_till(struct bpf_sock_addr, msg_src_ip6[0], + msg_src_ip6[3]): + switch (prog->expected_attach_type) { + case BPF_CGROUP_UDP6_SENDMSG: break; default: return false; @@ -5318,6 +5337,9 @@ static bool sock_addr_is_valid_access(int off, int size, switch (off) { case bpf_ctx_range(struct bpf_sock_addr, user_ip4): case bpf_ctx_range_till(struct bpf_sock_addr, user_ip6[0], user_ip6[3]): + case bpf_ctx_range(struct bpf_sock_addr, msg_src_ip4): + case bpf_ctx_range_till(struct bpf_sock_addr, msg_src_ip6[0], + msg_src_ip6[3]): /* Only narrow read access allowed for now. */ if (type == BPF_READ) { bpf_ctx_record_field_size(info, size_default); @@ -6072,6 +6094,23 @@ static u32 sock_addr_convert_ctx_access(enum bpf_access_type type, *insn++ = BPF_ALU32_IMM(BPF_RSH, si->dst_reg, SK_FL_PROTO_SHIFT); break; + + case offsetof(struct bpf_sock_addr, msg_src_ip4): + /* Treat t_ctx as struct in_addr for msg_src_ip4. */ + SOCK_ADDR_LOAD_OR_STORE_NESTED_FIELD_SIZE_OFF( + struct bpf_sock_addr_kern, struct in_addr, t_ctx, + s_addr, BPF_SIZE(si->code), 0, tmp_reg); + break; + + case bpf_ctx_range_till(struct bpf_sock_addr, msg_src_ip6[0], + msg_src_ip6[3]): + off = si->off; + off -= offsetof(struct bpf_sock_addr, msg_src_ip6[0]); + /* Treat t_ctx as struct in6_addr for msg_src_ip6. */ + SOCK_ADDR_LOAD_OR_STORE_NESTED_FIELD_SIZE_OFF( + struct bpf_sock_addr_kern, struct in6_addr, t_ctx, + s6_addr32[0], BPF_SIZE(si->code), off, tmp_reg); + break; } return insn - insn_buf; -- cgit v1.2.3