Subject: [PATCH bpf-next v1 06/19] bpf: support bpf tracing/iter programs for BPF_LINK_UPDATE

From: Yonghong Song <[email-masked]>
Date: Mon, 27 Apr 2020 13:12:41 -0700

Added BPF_LINK_UPDATE support for tracing/iter programs.
This way, a file based bpf iterator, which holds a reference
to the link, can have its bpf program updated without
creating new files.

Signed-off-by: Yonghong Song <[email-masked]>
---
 include/linux/bpf.h   |  2 ++
 kernel/bpf/bpf_iter.c | 29 +++++++++++++++++++++++++++++
 kernel/bpf/syscall.c  |  5 +++++
 3 files changed, 36 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 60ecb73d8f6d..4fc39d9b5cd0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1131,6 +1131,8 @@ struct bpf_prog *bpf_iter_get_prog(struct seq_file *seq, u32 priv_data_size,
 				   u64 *session_id, u64 *seq_num, bool is_last);
 int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
 int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
+			  struct bpf_prog *new_prog);
 
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 9532e7bcb8e1..fc1ce5ee5c3f 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -23,6 +23,9 @@ static struct list_head targets;
 static struct mutex targets_mutex;
 static bool bpf_iter_inited = false;
 
+/* protect bpf_iter_link.link->prog upddate */
+static struct mutex bpf_iter_mutex;
+
 int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
 {
 	struct bpf_iter_target_info *tinfo;
@@ -33,6 +36,7 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
 	if (!bpf_iter_inited) {
 		INIT_LIST_HEAD(&targets);
 		mutex_init(&targets_mutex);
+		mutex_init(&bpf_iter_mutex);
 		bpf_iter_inited = true;
 	}
 
@@ -121,3 +125,28 @@ int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 		kfree(link);
 	return err;
 }
+
+int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
+			  struct bpf_prog *new_prog)
+{
+	int ret = 0;
+
+	mutex_lock(&bpf_iter_mutex);
+	if (old_prog && link->prog != old_prog) {
+		ret = -EPERM;
+		goto out_unlock;
+	}
+
+	if (link->prog->type != new_prog->type ||
+	    link->prog->expected_attach_type != new_prog->expected_attach_type ||
+	    strcmp(link->prog->aux->attach_func_name, new_prog->aux->attach_func_name)) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	link->prog = new_prog;
+
+out_unlock:
+	mutex_unlock(&bpf_iter_mutex);
+	return ret;
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8741b5e11c85..b7af4f006f2e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3679,6 +3679,11 @@ static int link_update(union bpf_attr *attr)
 		goto out_put_progs;
 	}
 #endif
+
+	if (link->ops == &bpf_iter_link_lops) {
+		ret = bpf_iter_link_replace(link, old_prog, new_prog);
+		goto out_put_progs;
+	}
 	ret = -EINVAL;
 
 out_put_progs:
-- 
2.24.1