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authorMartin KaFai Lau <kafai@fb.com>2021-08-24 10:30:07 -0700
committerAlexei Starovoitov <ast@kernel.org>2021-08-25 17:40:35 -0700
commiteb18b49ea758ec052ac2a12c6bb204e1e877ec31 (patch)
tree25b1abda9fa79a60a006ec13ec752307cba2c91f /net/ipv4
parent7d789bd0089ad2a6cc2315f281018bfafae820bc (diff)
downloadlinux-eb18b49ea758ec052ac2a12c6bb204e1e877ec31.tar.bz2
bpf: tcp: Allow bpf-tcp-cc to call bpf_(get|set)sockopt
This patch allows the bpf-tcp-cc to call bpf_setsockopt. One use case is to allow a bpf-tcp-cc switching to another cc during init(). For example, when the tcp flow is not ecn ready, the bpf_dctcp can switch to another cc by calling setsockopt(TCP_CONGESTION). During setsockopt(TCP_CONGESTION), the new tcp-cc's init() will be called and this could cause a recursion but it is stopped by the current trampoline's logic (in the prog->active counter). While retiring a bpf-tcp-cc (e.g. in tcp_v[46]_destroy_sock()), the tcp stack calls bpf-tcp-cc's release(). To avoid the retiring bpf-tcp-cc making further changes to the sk, bpf_setsockopt is not available to the bpf-tcp-cc's release(). This will avoid release() making setsockopt() call that will potentially allocate new resources. Although the bpf-tcp-cc already has a more powerful way to read tcp_sock from the PTR_TO_BTF_ID, it is usually expected that bpf_getsockopt and bpf_setsockopt are available together. Thus, bpf_getsockopt() is also added to all tcp_congestion_ops except release(). When the old bpf-tcp-cc is calling setsockopt(TCP_CONGESTION) to switch to a new cc, the old bpf-tcp-cc will be released by bpf_struct_ops_put(). Thus, this patch also puts the bpf_struct_ops_map after a rcu grace period because the trampoline's image cannot be freed while the old bpf-tcp-cc is still running. bpf-tcp-cc can only access icsk_ca_priv as SCALAR. All kernel's tcp-cc is also accessing the icsk_ca_priv as SCALAR. The size of icsk_ca_priv has already been raised a few times to avoid extra kmalloc and memory referencing. The only exception is the kernel's tcp_cdg.c that stores a kmalloc()-ed pointer in icsk_ca_priv. To avoid the old bpf-tcp-cc accidentally overriding this tcp_cdg's pointer value stored in icsk_ca_priv after switching and without over-complicating the bpf's verifier for this one exception in tcp_cdg, this patch does not allow switching to tcp_cdg. If there is a need, bpf_tcp_cdg can be implemented and then use the bpf_sk_storage as the extended storage. bpf_sk_setsockopt proto has only been recently added and used in bpf-sockopt and bpf-iter-tcp, so impose the tcp_cdg limitation in the same proto instead of adding a new proto specifically for bpf-tcp-cc. Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20210824173007.3976921-1-kafai@fb.com
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/bpf_tcp_ca.c41
1 files changed, 38 insertions, 3 deletions
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 9e41eff4a685..0dcee9df1326 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -10,6 +10,9 @@
#include <net/tcp.h>
#include <net/bpf_sk_storage.h>
+/* "extern" is to avoid sparse warning. It is only used in bpf_struct_ops.c. */
+extern struct bpf_struct_ops bpf_tcp_congestion_ops;
+
static u32 optional_ops[] = {
offsetof(struct tcp_congestion_ops, init),
offsetof(struct tcp_congestion_ops, release),
@@ -163,6 +166,19 @@ static const struct bpf_func_proto bpf_tcp_send_ack_proto = {
.arg2_type = ARG_ANYTHING,
};
+static u32 prog_ops_moff(const struct bpf_prog *prog)
+{
+ const struct btf_member *m;
+ const struct btf_type *t;
+ u32 midx;
+
+ midx = prog->expected_attach_type;
+ t = bpf_tcp_congestion_ops.type;
+ m = &btf_type_member(t)[midx];
+
+ return btf_member_bit_offset(t, m) / 8;
+}
+
static const struct bpf_func_proto *
bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id,
const struct bpf_prog *prog)
@@ -174,6 +190,28 @@ bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id,
return &bpf_sk_storage_get_proto;
case BPF_FUNC_sk_storage_delete:
return &bpf_sk_storage_delete_proto;
+ case BPF_FUNC_setsockopt:
+ /* Does not allow release() to call setsockopt.
+ * release() is called when the current bpf-tcp-cc
+ * is retiring. It is not allowed to call
+ * setsockopt() to make further changes which
+ * may potentially allocate new resources.
+ */
+ if (prog_ops_moff(prog) !=
+ offsetof(struct tcp_congestion_ops, release))
+ return &bpf_sk_setsockopt_proto;
+ return NULL;
+ case BPF_FUNC_getsockopt:
+ /* Since get/setsockopt is usually expected to
+ * be available together, disable getsockopt for
+ * release also to avoid usage surprise.
+ * The bpf-tcp-cc already has a more powerful way
+ * to read tcp_sock from the PTR_TO_BTF_ID.
+ */
+ if (prog_ops_moff(prog) !=
+ offsetof(struct tcp_congestion_ops, release))
+ return &bpf_sk_getsockopt_proto;
+ return NULL;
default:
return bpf_base_func_proto(func_id);
}
@@ -286,9 +324,6 @@ static void bpf_tcp_ca_unreg(void *kdata)
tcp_unregister_congestion_control(kdata);
}
-/* Avoid sparse warning. It is only used in bpf_struct_ops.c. */
-extern struct bpf_struct_ops bpf_tcp_congestion_ops;
-
struct bpf_struct_ops bpf_tcp_congestion_ops = {
.verifier_ops = &bpf_tcp_ca_verifier_ops,
.reg = bpf_tcp_ca_reg,