diff options
author | Martin KaFai Lau <kafai@fb.com> | 2021-08-24 20:30:07 +0300 |
---|---|---|
committer | Alexei Starovoitov <ast@kernel.org> | 2021-08-26 03:40:35 +0300 |
commit | eb18b49ea758ec052ac2a12c6bb204e1e877ec31 (patch) | |
tree | 25b1abda9fa79a60a006ec13ec752307cba2c91f /net/ipv4 | |
parent | 7d789bd0089ad2a6cc2315f281018bfafae820bc (diff) | |
download | linux-eb18b49ea758ec052ac2a12c6bb204e1e877ec31.tar.xz |
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.c | 41 |
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, |