Merge branch 'Support direct writes to nf_conn:mark'

Daniel Xu says:

====================

Support direct writes to nf_conn:mark from TC and XDP prog types. This
is useful when applications want to store per-connection metadata. This
is also particularly useful for applications that run both bpf and
iptables/nftables because the latter can trivially access this metadata.

One example use case would be if a bpf prog is responsible for advanced
packet classification and iptables/nftables is later used for routing
due to pre-existing/legacy code.

Past discussion:
- v4: https://lore.kernel.org/bpf/cover.1661192455.git.dxu@dxuuu.xyz/
- v3: https://lore.kernel.org/bpf/cover.1660951028.git.dxu@dxuuu.xyz/
- v2: https://lore.kernel.org/bpf/CAP01T74Sgn354dXGiFWFryu4vg+o8b9s9La1d9zEbC4LGvH4qg@mail.gmail.com/T/
- v1: https://lore.kernel.org/bpf/cover.1660592020.git.dxu@dxuuu.xyz/

Changes since v4:
- Use exported function pointer + mutex to handle CONFIG_NF_CONNTRACK=m
  case

Changes since v3:
- Use a mutex to protect module load/unload critical section

Changes since v2:
- Remove use of NOT_INIT for btf_struct_access write path
- Disallow nf_conn writing when nf_conntrack module not loaded
- Support writing to nf_conn___init:mark

Changes since v1:
- Add unimplemented stub for when !CONFIG_BPF_SYSCALL
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 48ae05099f36..54178b9e9c3a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2211,6 +2211,15 @@ static inline struct bpf_prog *bpf_prog_by_id(u32 id)
 	return ERR_PTR(-ENOTSUPP);
 }
 
+static inline int btf_struct_access(struct bpf_verifier_log *log,
+				    const struct btf *btf,
+				    const struct btf_type *t, int off, int size,
+				    enum bpf_access_type atype,
+				    u32 *next_btf_id, enum bpf_type_flag *flag)
+{
+	return -EACCES;
+}
+
 static inline const struct bpf_func_proto *
 bpf_base_func_proto(enum bpf_func_id func_id)
 {