[PATCH bpf-next 2/9] bpf: Add log support for tracing_multi link_create

[Leon Hwang]

tracing_multi BPF_LINK_CREATE returns an error for invalid counts, missing
IDs, unsupported flags, or a nonzero target FD without explaining which
check failed.

Report these failures through the BPF_LINK_CREATE log.

Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
---
 include/linux/trace_events.h |  7 +++++--
 kernel/bpf/syscall.c         |  2 +-
 kernel/trace/bpf_trace.c     | 26 +++++++++++++++++++++-----
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 321f2f3a6c8e..bb825ea5d09c 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -16,6 +16,7 @@ struct tracer;
 struct dentry;
 struct bpf_prog;
 union bpf_attr;
+struct bpf_verifier_log;
 
 /* Used for event string fields when they are NULL */
 #define EVENT_NULL_STR		"(null)"
@@ -796,7 +797,8 @@ int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
 			    unsigned long *missed);
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
 int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
-int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr);
+int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr,
+			     struct bpf_verifier_log *log);
 #else
 static inline unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
 {
@@ -855,7 +857,8 @@ bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	return -EOPNOTSUPP;
 }
 static inline int
-bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr)
+bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr,
+			 struct bpf_verifier_log *log)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6147d386b777..aed1c6a2f203 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5932,7 +5932,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 		else if (prog->expected_attach_type == BPF_LSM_CGROUP)
 			ret = cgroup_bpf_link_attach(attr, prog);
 		else if (is_tracing_multi(prog->expected_attach_type))
-			ret = bpf_tracing_multi_attach(prog, attr);
+			ret = bpf_tracing_multi_attach(prog, attr, log);
 		else
 			ret = bpf_tracing_prog_attach(prog,
 						      attr->link_create.target_fd,
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2aec56d7f3d3..352a1cd0c863 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3861,7 +3861,8 @@ static int check_dup_ids(u32 *ids, u64 *cookies, u32 cnt)
 	return err;
 }
 
-int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr)
+int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr,
+			     struct bpf_verifier_log *log)
 {
 	struct bpf_tracing_multi_link *link = NULL;
 	struct bpf_tramp_node *fexits = NULL;
@@ -3875,12 +3876,26 @@ int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr)
 	uids = u64_to_user_ptr(attr->link_create.tracing_multi.ids);
 	cnt = attr->link_create.tracing_multi.cnt;
 
-	if (!cnt || !uids)
+	if (!cnt) {
+		bpf_log(log, "tracing_multi.cnt cannot be zero.\n");
 		return -EINVAL;
-	if (cnt > MAX_TRACING_MULTI_CNT)
+	}
+	if (!uids) {
+		bpf_log(log, "tracing_multi.ids must be set.\n");
+		return -EINVAL;
+	}
+	if (cnt > MAX_TRACING_MULTI_CNT) {
+		bpf_log(log, "tracing_multi.cnt is too large.\n");
 		return -E2BIG;
-	if (attr->link_create.flags || attr->link_create.target_fd)
+	}
+	if (attr->link_create.flags) {
+		bpf_log(log, "Invalid flags.\n");
 		return -EINVAL;
+	}
+	if (attr->link_create.target_fd) {
+		bpf_log(log, "Invalid target_fd.\n");
+		return -EINVAL;
+	}
 
 	ids = kvmalloc_objs(*ids, cnt);
 	if (!ids)
@@ -3951,7 +3966,8 @@ int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr)
 
 #else
 
-int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr)
+int bpf_tracing_multi_attach(struct bpf_prog *prog, const union bpf_attr *attr,
+			     struct bpf_verifier_log *log)
 {
 	return -EOPNOTSUPP;
 }
-- 
2.55.0