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Date: Wed, 7 Sep 2022 10:40:40 -0600
From: Daniel Xu <dxu@...uu.xyz>
To: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, memxor@...il.com
Cc: Daniel Xu <dxu@...uu.xyz>, pablo@...filter.org, fw@...len.de,
toke@...nel.org, martin.lau@...ux.dev,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v5 5/6] bpf: Add support for writing to nf_conn:mark
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@...uu.xyz>
---
include/net/netfilter/nf_conntrack_bpf.h | 23 +++++++++
net/core/filter.c | 54 +++++++++++++++++++
net/netfilter/nf_conntrack_bpf.c | 66 +++++++++++++++++++++++-
net/netfilter/nf_conntrack_core.c | 1 +
4 files changed, 143 insertions(+), 1 deletion(-)
diff --git a/include/net/netfilter/nf_conntrack_bpf.h b/include/net/netfilter/nf_conntrack_bpf.h
index a473b56842c5..a61a93d1c6dc 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>
+#include <linux/mutex.h>
#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);
+
+extern struct mutex nf_conn_btf_access_lock;
+extern int (*nfct_bsa)(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);
#else
@@ -18,6 +27,20 @@ static inline int register_nf_conntrack_bpf(void)
return 0;
}
+static inline void cleanup_nf_conntrack_bpf(void)
+{
+}
+
+static inline 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)
+{
+ return -EACCES;
+}
+
#endif
#endif /* _NF_CONNTRACK_BPF_H */
diff --git a/net/core/filter.c b/net/core/filter.c
index e872f45399b0..4b2be211bcbe 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>
@@ -8604,6 +8605,36 @@ static bool tc_cls_act_is_valid_access(int off, int size,
return bpf_skb_is_valid_access(off, size, type, prog, info);
}
+DEFINE_MUTEX(nf_conn_btf_access_lock);
+EXPORT_SYMBOL_GPL(nf_conn_btf_access_lock);
+
+int (*nfct_bsa)(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);
+EXPORT_SYMBOL_GPL(nfct_bsa);
+
+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)
+{
+ int ret = -EACCES;
+
+ if (atype == BPF_READ)
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
+
+ mutex_lock(&nf_conn_btf_access_lock);
+ if (nfct_bsa)
+ ret = nfct_bsa(log, btf, t, off, size, atype, next_btf_id, flag);
+ mutex_unlock(&nf_conn_btf_access_lock);
+
+ return ret;
+}
+
static bool __is_valid_xdp_access(int off, int size)
{
if (off < 0 || off >= sizeof(struct xdp_md))
@@ -8663,6 +8694,27 @@ 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)
+{
+ int ret = -EACCES;
+
+ if (atype == BPF_READ)
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
+
+ mutex_lock(&nf_conn_btf_access_lock);
+ if (nfct_bsa)
+ ret = nfct_bsa(log, btf, t, off, size, atype, next_btf_id, flag);
+ mutex_unlock(&nf_conn_btf_access_lock);
+
+ return ret;
+}
+
static bool sock_addr_is_valid_access(int off, int size,
enum bpf_access_type type,
const struct bpf_prog *prog,
@@ -10557,6 +10609,7 @@ 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 = {
@@ -10568,6 +10621,7 @@ 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..77eb8e959f61 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -6,8 +6,10 @@
* are exposed through to BPF programs is explicitly unstable.
*/
+#include <linux/bpf_verifier.h>
#include <linux/bpf.h>
#include <linux/btf.h>
+#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/btf_ids.h>
#include <linux/net_namespace.h>
@@ -184,6 +186,54 @@ 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;
+ const struct btf_type *nct;
+ size_t end;
+
+ ncit = btf_type_by_id(btf, btf_nf_conn_ids[1]);
+ nct = btf_type_by_id(btf, btf_nf_conn_ids[0]);
+
+ 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 +499,19 @@ 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) {
+ mutex_lock(&nf_conn_btf_access_lock);
+ nfct_bsa = _nf_conntrack_btf_struct_access;
+ mutex_unlock(&nf_conn_btf_access_lock);
+ }
+
+ return ret;
+}
+
+void cleanup_nf_conntrack_bpf(void)
+{
+ mutex_lock(&nf_conn_btf_access_lock);
+ nfct_bsa = NULL;
+ mutex_unlock(&nf_conn_btf_access_lock);
}
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
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