bpf: Check attach type at prog load time

== The problem ==

There are use-cases when a program of some type can be attached to
multiple attach points and those attach points must have different
permissions to access context or to call helpers.

E.g. context structure may have fields for both IPv4 and IPv6 but it
doesn't make sense to read from / write to IPv6 field when attach point
is somewhere in IPv4 stack.

Same applies to BPF-helpers: it may make sense to call some helper from
some attach point, but not from other for same prog type.

== The solution ==

Introduce `expected_attach_type` field in in `struct bpf_attr` for
`BPF_PROG_LOAD` command. If scenario described in "The problem" section
is the case for some prog type, the field will be checked twice:

1) At load time prog type is checked to see if attach type for it must
   be known to validate program permissions correctly. Prog will be
   rejected with EINVAL if it's the case and `expected_attach_type` is
   not specified or has invalid value.

2) At attach time `attach_type` is compared with `expected_attach_type`,
   if prog type requires to have one, and, if they differ, attach will
   be rejected with EINVAL.

The `expected_attach_type` is now available as part of `struct bpf_prog`
in both `bpf_verifier_ops->is_valid_access()` and
`bpf_verifier_ops->get_func_proto()` () and can be used to check context
accesses and calls to helpers correspondingly.

Initially the idea was discussed by Alexei Starovoitov <ast@fb.com> and
Daniel Borkmann <daniel@iogearbox.net> here:
https://marc.info/?l=linux-netdev&m=152107378717201&w=2

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 25 insertions, 14 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index e989bf3..7790fd1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3685,7 +3685,7 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-sock_filter_func_proto(enum bpf_func_id func_id)
+sock_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	/* inet and inet6 sockets are created in a process
@@ -3699,7 +3699,7 @@ sock_filter_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-sk_filter_func_proto(enum bpf_func_id func_id)
+sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_skb_load_bytes:
@@ -3714,7 +3714,7 @@ sk_filter_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-tc_cls_act_func_proto(enum bpf_func_id func_id)
+tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_skb_store_bytes:
@@ -3781,7 +3781,7 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-xdp_func_proto(enum bpf_func_id func_id)
+xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_perf_event_output:
@@ -3804,7 +3804,7 @@ xdp_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-lwt_inout_func_proto(enum bpf_func_id func_id)
+lwt_inout_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_skb_load_bytes:
@@ -3831,7 +3831,7 @@ lwt_inout_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-	sock_ops_func_proto(enum bpf_func_id func_id)
+sock_ops_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_setsockopt:
@@ -3847,7 +3847,8 @@ static const struct bpf_func_proto *
 	}
 }
 
-static const struct bpf_func_proto *sk_msg_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+sk_msg_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_msg_redirect_map:
@@ -3863,7 +3864,8 @@ static const struct bpf_func_proto *sk_msg_func_proto(enum bpf_func_id func_id)
 	}
 }
 
-static const struct bpf_func_proto *sk_skb_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *
+sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_skb_store_bytes:
@@ -3888,7 +3890,7 @@ static const struct bpf_func_proto *sk_skb_func_proto(enum bpf_func_id func_id)
 }
 
 static const struct bpf_func_proto *
-lwt_xmit_func_proto(enum bpf_func_id func_id)
+lwt_xmit_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_skb_get_tunnel_key:
@@ -3918,11 +3920,12 @@ lwt_xmit_func_proto(enum bpf_func_id func_id)
 	case BPF_FUNC_set_hash_invalid:
 		return &bpf_set_hash_invalid_proto;
 	default:
-		return lwt_inout_func_proto(func_id);
+		return lwt_inout_func_proto(func_id, prog);
 	}
 }
 
 static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type,
+				    const struct bpf_prog *prog,
 				    struct bpf_insn_access_aux *info)
 {
 	const int size_default = sizeof(__u32);
@@ -3966,6 +3969,7 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type
 
 static bool sk_filter_is_valid_access(int off, int size,
 				      enum bpf_access_type type,
+				      const struct bpf_prog *prog,
 				      struct bpf_insn_access_aux *info)
 {
 	switch (off) {
@@ -3986,11 +3990,12 @@ static bool sk_filter_is_valid_access(int off, int size,
 		}
 	}
 
-	return bpf_skb_is_valid_access(off, size, type, info);
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
 }
 
 static bool lwt_is_valid_access(int off, int size,
 				enum bpf_access_type type,
+				const struct bpf_prog *prog,
 				struct bpf_insn_access_aux *info)
 {
 	switch (off) {
@@ -4020,11 +4025,12 @@ static bool lwt_is_valid_access(int off, int size,
 		break;
 	}
 
-	return bpf_skb_is_valid_access(off, size, type, info);
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
 }
 
 static bool sock_filter_is_valid_access(int off, int size,
 					enum bpf_access_type type,
+					const struct bpf_prog *prog,
 					struct bpf_insn_access_aux *info)
 {
 	if (type == BPF_WRITE) {
@@ -4096,6 +4102,7 @@ static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
 
 static bool tc_cls_act_is_valid_access(int off, int size,
 				       enum bpf_access_type type,
+				       const struct bpf_prog *prog,
 				       struct bpf_insn_access_aux *info)
 {
 	if (type == BPF_WRITE) {
@@ -4125,7 +4132,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
 		return false;
 	}
 
-	return bpf_skb_is_valid_access(off, size, type, info);
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
 }
 
 static bool __is_valid_xdp_access(int off, int size)
@@ -4142,6 +4149,7 @@ static bool __is_valid_xdp_access(int off, int size)
 
 static bool xdp_is_valid_access(int off, int size,
 				enum bpf_access_type type,
+				const struct bpf_prog *prog,
 				struct bpf_insn_access_aux *info)
 {
 	if (type == BPF_WRITE)
@@ -4174,6 +4182,7 @@ EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
 
 static bool sock_ops_is_valid_access(int off, int size,
 				     enum bpf_access_type type,
+				     const struct bpf_prog *prog,
 				     struct bpf_insn_access_aux *info)
 {
 	const int size_default = sizeof(__u32);
@@ -4220,6 +4229,7 @@ static int sk_skb_prologue(struct bpf_insn *insn_buf, bool direct_write,
 
 static bool sk_skb_is_valid_access(int off, int size,
 				   enum bpf_access_type type,
+				   const struct bpf_prog *prog,
 				   struct bpf_insn_access_aux *info)
 {
 	switch (off) {
@@ -4249,11 +4259,12 @@ static bool sk_skb_is_valid_access(int off, int size,
 		break;
 	}
 
-	return bpf_skb_is_valid_access(off, size, type, info);
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
 }
 
 static bool sk_msg_is_valid_access(int off, int size,
 				   enum bpf_access_type type,
+				   const struct bpf_prog *prog,
 				   struct bpf_insn_access_aux *info)
 {
 	if (type == BPF_WRITE)