[PATCH bpf-next v3 4/5] bpf: Add support for writing to nf_conn:mark
From: Daniel Xu
Date: Fri Aug 19 2022 - 19:24:19 EST
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.
Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
---
include/net/netfilter/nf_conntrack_bpf.h | 13 +++++
net/core/filter.c | 50 ++++++++++++++++++
net/netfilter/nf_conntrack_bpf.c | 64 +++++++++++++++++++++++-
net/netfilter/nf_conntrack_core.c | 1 +
4 files changed, 127 insertions(+), 1 deletion(-)
diff --git a/include/net/netfilter/nf_conntrack_bpf.h b/include/net/netfilter/nf_conntrack_bpf.h
index a473b56842c5..4ef89ee5b5a9 100644
--- a/include/net/netfilter/nf_conntrack_bpf.h
+++ b/include/net/netfilter/nf_conntrack_bpf.h
@@ -3,13 +3,22 @@
#ifndef _NF_CONNTRACK_BPF_H
#define _NF_CONNTRACK_BPF_H
+#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/kconfig.h>
+extern int (*nf_conntrack_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);
+
#if (IS_BUILTIN(CONFIG_NF_CONNTRACK) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) || \
(IS_MODULE(CONFIG_NF_CONNTRACK) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
extern int register_nf_conntrack_bpf(void);
+extern void cleanup_nf_conntrack_bpf(void);
#else
@@ -18,6 +27,10 @@ static inline int register_nf_conntrack_bpf(void)
return 0;
}
+static inline void cleanup_nf_conntrack_bpf(void)
+{
+}
+
#endif
#endif /* _NF_CONNTRACK_BPF_H */
diff --git a/net/core/filter.c b/net/core/filter.c
index 1acfaffeaf32..e5f48e6030b7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -18,6 +18,7 @@
*/
#include <linux/atomic.h>
+#include <linux/bpf_verifier.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
@@ -55,6 +56,7 @@
#include <net/sock_reuseport.h>
#include <net/busy_poll.h>
#include <net/tcp.h>
+#include <net/netfilter/nf_conntrack_bpf.h>
#include <net/xfrm.h>
#include <net/udp.h>
#include <linux/bpf_trace.h>
@@ -8628,6 +8630,32 @@ static bool tc_cls_act_is_valid_access(int off, int size,
return bpf_skb_is_valid_access(off, size, type, prog, info);
}
+typedef int (*btf_struct_access_t)(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);
+
+static int tc_cls_act_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)
+{
+ btf_struct_access_t sa;
+
+ if (atype == BPF_READ)
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
+
+ sa = READ_ONCE(nf_conntrack_btf_struct_access);
+ if (sa)
+ return sa(log, btf, t, off, size, atype, next_btf_id, flag);
+
+ return -EACCES;
+}
+
static bool __is_valid_xdp_access(int off, int size)
{
if (off < 0 || off >= sizeof(struct xdp_md))
@@ -8687,6 +8715,26 @@ void bpf_warn_invalid_xdp_action(struct net_device *dev, struct bpf_prog *prog,
}
EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
+static int xdp_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)
+{
+ btf_struct_access_t sa;
+
+ if (atype == BPF_READ)
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
+
+ sa = READ_ONCE(nf_conntrack_btf_struct_access);
+ if (sa)
+ return sa(log, btf, t, off, size, atype, next_btf_id, flag);
+
+ return -EACCES;
+}
+
static bool sock_addr_is_valid_access(int off, int size,
enum bpf_access_type type,
const struct bpf_prog *prog,
@@ -10581,6 +10629,7 @@ const struct bpf_verifier_ops tc_cls_act_verifier_ops = {
.convert_ctx_access = tc_cls_act_convert_ctx_access,
.gen_prologue = tc_cls_act_prologue,
.gen_ld_abs = bpf_gen_ld_abs,
+ .btf_struct_access = tc_cls_act_btf_struct_access,
};
const struct bpf_prog_ops tc_cls_act_prog_ops = {
@@ -10592,6 +10641,7 @@ const struct bpf_verifier_ops xdp_verifier_ops = {
.is_valid_access = xdp_is_valid_access,
.convert_ctx_access = xdp_convert_ctx_access,
.gen_prologue = bpf_noop_prologue,
+ .btf_struct_access = xdp_btf_struct_access,
};
const struct bpf_prog_ops xdp_prog_ops = {
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index 1cd87b28c9b0..a346b561981a 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -6,6 +6,7 @@
* are exposed through to BPF programs is explicitly unstable.
*/
+#include <linux/bpf_verifier.h>
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/types.h>
@@ -15,6 +16,13 @@
#include <net/netfilter/nf_conntrack_bpf.h>
#include <net/netfilter/nf_conntrack_core.h>
+int (*nf_conntrack_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);
+
/* bpf_ct_opts - Options for CT lookup helpers
*
* Members:
@@ -184,6 +192,51 @@ static struct nf_conn *__bpf_nf_ct_lookup(struct net *net,
return ct;
}
+BTF_ID_LIST(btf_nf_conn_ids)
+BTF_ID(struct, nf_conn)
+BTF_ID(struct, nf_conn___init)
+
+/* Check writes into `struct nf_conn` */
+static int _nf_conntrack_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)
+{
+ const struct btf_type *ncit = btf_type_by_id(btf, btf_nf_conn_ids[1]);
+ const struct btf_type *nct = btf_type_by_id(btf, btf_nf_conn_ids[0]);
+ size_t end;
+
+ if (t != nct && t != ncit) {
+ bpf_log(log, "only read is supported\n");
+ return -EACCES;
+ }
+
+ /* `struct nf_conn` and `struct nf_conn___init` have the same layout
+ * so we are safe to simply merge offset checks here
+ */
+ switch (off) {
+#if defined(CONFIG_NF_CONNTRACK_MARK)
+ case offsetof(struct nf_conn, mark):
+ end = offsetofend(struct nf_conn, mark);
+ break;
+#endif
+ default:
+ bpf_log(log, "no write support to nf_conn at off %d\n", off);
+ return -EACCES;
+ }
+
+ if (off + size > end) {
+ bpf_log(log,
+ "write access at off %d with size %d beyond the member of nf_conn ended at %zu\n",
+ off, size, end);
+ return -EACCES;
+ }
+
+ return 0;
+}
+
__diag_push();
__diag_ignore_all("-Wmissing-prototypes",
"Global functions as their definitions will be in nf_conntrack BTF");
@@ -449,5 +502,14 @@ int register_nf_conntrack_bpf(void)
int ret;
ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &nf_conntrack_kfunc_set);
- return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &nf_conntrack_kfunc_set);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &nf_conntrack_kfunc_set);
+ if (!ret)
+ WRITE_ONCE(nf_conntrack_btf_struct_access, _nf_conntrack_btf_struct_access);
+
+ return ret;
+}
+
+void cleanup_nf_conntrack_bpf(void)
+{
+ WRITE_ONCE(nf_conntrack_btf_struct_access, NULL);
}
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index da65c6e8eeeb..0195f60fc43b 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -2512,6 +2512,7 @@ static int kill_all(struct nf_conn *i, void *data)
void nf_conntrack_cleanup_start(void)
{
+ cleanup_nf_conntrack_bpf();
conntrack_gc_work.exiting = true;
}
--
2.37.1