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Date: Wed, 4 Aug 2021 22:01:25 -0700
From: Martin KaFai Lau <kafai@...com>
To: <bpf@...r.kernel.org>
CC: Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
<netdev@...r.kernel.org>
Subject: [PATCH bpf-next 1/4] 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.
bpf_getsockopt() is also added to have a symmetrical API, so
less usage surprise.
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.
Signed-off-by: Martin KaFai Lau <kafai@...com>
---
kernel/bpf/bpf_struct_ops.c | 22 +++++++++++++++++++++-
net/ipv4/bpf_tcp_ca.c | 26 +++++++++++++++++++++++---
2 files changed, 44 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 70f6fd4fa305..d6731c32864e 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -28,6 +28,7 @@ struct bpf_struct_ops_value {
struct bpf_struct_ops_map {
struct bpf_map map;
+ struct rcu_head rcu;
const struct bpf_struct_ops *st_ops;
/* protect map_update */
struct mutex lock;
@@ -622,6 +623,14 @@ bool bpf_struct_ops_get(const void *kdata)
return refcount_inc_not_zero(&kvalue->refcnt);
}
+static void bpf_struct_ops_put_rcu(struct rcu_head *head)
+{
+ struct bpf_struct_ops_map *st_map;
+
+ st_map = container_of(head, struct bpf_struct_ops_map, rcu);
+ bpf_map_put(&st_map->map);
+}
+
void bpf_struct_ops_put(const void *kdata)
{
struct bpf_struct_ops_value *kvalue;
@@ -632,6 +641,17 @@ void bpf_struct_ops_put(const void *kdata)
st_map = container_of(kvalue, struct bpf_struct_ops_map,
kvalue);
- bpf_map_put(&st_map->map);
+ /* The struct_ops's function may switch to another struct_ops.
+ *
+ * For example, bpf_tcp_cc_x->init() may switch to
+ * another tcp_cc_y by calling
+ * setsockopt(TCP_CONGESTION, "tcp_cc_y").
+ * During the switch, bpf_struct_ops_put(tcp_cc_x) is called
+ * and its map->refcnt may reach 0 which then free its
+ * trampoline image while tcp_cc_x is still running.
+ *
+ * Thus, a rcu grace period is needed here.
+ */
+ call_rcu(&st_map->rcu, bpf_struct_ops_put_rcu);
}
}
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 9e41eff4a685..00db0ce3af43 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),
@@ -167,6 +170,10 @@ static const struct bpf_func_proto *
bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id,
const struct bpf_prog *prog)
{
+ const struct btf_member *m;
+ const struct btf_type *t;
+ u32 moff, midx;
+
switch (func_id) {
case BPF_FUNC_tcp_send_ack:
return &bpf_tcp_send_ack_proto;
@@ -174,6 +181,22 @@ 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.
+ */
+ midx = prog->expected_attach_type;
+ t = bpf_tcp_congestion_ops.type;
+ m = &btf_type_member(t)[midx];
+ moff = btf_member_bit_offset(t, m) / 8;
+ if (moff == offsetof(struct tcp_congestion_ops, release))
+ return NULL;
+ return &bpf_sk_setsockopt_proto;
+ case BPF_FUNC_getsockopt:
+ return &bpf_sk_getsockopt_proto;
default:
return bpf_base_func_proto(func_id);
}
@@ -286,9 +309,6 @@ 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,
--
2.30.2
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