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authorJoe Stringer <joe@wand.net.nz>2018-10-02 13:35:36 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2018-10-03 02:53:47 +0200
commit6acc9b432e6714d72d7d77ec7c27f6f8358d0c71 (patch)
tree1b5ac6b607e8d88a815c8b88d795e71a18260f31 /kernel/bpf
parentfd978bf7fd312581a7ca454a991f0ffb34c4204b (diff)
bpf: Add helper to retrieve socket in BPF
This patch adds new BPF helper functions, bpf_sk_lookup_tcp() and bpf_sk_lookup_udp() which allows BPF programs to find out if there is a socket listening on this host, and returns a socket pointer which the BPF program can then access to determine, for instance, whether to forward or drop traffic. bpf_sk_lookup_xxx() may take a reference on the socket, so when a BPF program makes use of this function, it must subsequently pass the returned pointer into the newly added sk_release() to return the reference. By way of example, the following pseudocode would filter inbound connections at XDP if there is no corresponding service listening for the traffic: struct bpf_sock_tuple tuple; struct bpf_sock_ops *sk; populate_tuple(ctx, &tuple); // Extract the 5tuple from the packet sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof tuple, netns, 0); if (!sk) { // Couldn't find a socket listening for this traffic. Drop. return TC_ACT_SHOT; } bpf_sk_release(sk, 0); return TC_ACT_OK; Signed-off-by: Joe Stringer <joe@wand.net.nz> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/verifier.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cd0d8bc00bd1..73c81bef6ae8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -153,6 +153,12 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
* PTR_TO_MAP_VALUE, PTR_TO_SOCKET_OR_NULL becomes PTR_TO_SOCKET when the type
* passes through a NULL-check conditional. For the branch wherein the state is
* changed to CONST_IMM, the verifier releases the reference.
+ *
+ * For each helper function that allocates a reference, such as
+ * bpf_sk_lookup_tcp(), there is a corresponding release function, such as
+ * bpf_sk_release(). When a reference type passes into the release function,
+ * the verifier also releases the reference. If any unchecked or unreleased
+ * reference remains at the end of the program, the verifier rejects it.
*/
/* verifier_state + insn_idx are pushed to stack when branch is encountered */
@@ -300,7 +306,7 @@ static bool arg_type_is_refcounted(enum bpf_arg_type type)
*/
static bool is_release_function(enum bpf_func_id func_id)
{
- return false;
+ return func_id == BPF_FUNC_sk_release;
}
/* string representation of 'enum bpf_reg_type' */