[PATCH bpf-next 1/6] bpf: Add syscall common attrs support for link_create

[Leon Hwang <leon.hwang@linux.dev>]

Similar to the syscall common attrs support for map_create [1], add the
syscall common attrs support for link_create.

Create and finalize the internal verifier log instance.

Then, report the error messages for invalid prog fd and invalid attach
type.

Links:
[1] https://lore.kernel.org/bpf/20260514004634.3DA09C19425@smtp.kernel.org/

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/bpf/syscall.c | 34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0f27604a54aa..252b479937a4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5839,10 +5839,13 @@ static int bpf_map_do_batch(const union bpf_attr *attr,
 }
 
 #define BPF_LINK_CREATE_LAST_FIELD link_create.uprobe_multi.path_fd
-static int link_create(union bpf_attr *attr, bpfptr_t uattr)
+static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_attr *attr_common,
+		       bpfptr_t uattr_common, u32 size_common)
 {
+	struct bpf_verifier_log *log;
+	struct bpf_log_attr attr_log;
 	struct bpf_prog *prog;
-	int ret;
+	int ret, err;
 
 	if (CHECK_ATTR(BPF_LINK_CREATE))
 		return -EINVAL;
@@ -5850,14 +5853,24 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	if (attr->link_create.attach_type == BPF_STRUCT_OPS)
 		return bpf_struct_ops_link_create(attr);
 
+	log = bpf_log_attr_create_vlog(&attr_log, attr_common, uattr_common, size_common);
+	if (IS_ERR(log))
+		return PTR_ERR(log);
+
 	prog = bpf_prog_get(attr->link_create.prog_fd);
-	if (IS_ERR(prog))
-		return PTR_ERR(prog);
+	if (IS_ERR(prog)) {
+		bpf_log(log, "Invalid prog_fd.\n");
+		ret = PTR_ERR(prog);
+		prog = NULL;
+		goto out;
+	}
 
 	ret = bpf_prog_attach_check_attach_type(prog,
 						attr->link_create.attach_type);
-	if (ret)
+	if (ret) {
+		bpf_log(log, "Invalid attach_type.\n");
 		goto out;
+	}
 
 	switch (prog->type) {
 	case BPF_PROG_TYPE_CGROUP_SKB:
@@ -5940,7 +5953,14 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	}
 
 out:
-	if (ret < 0)
+	/* preserve original error even if log finalization is successful */
+	err = bpf_log_attr_finalize(&attr_log, log);
+	if (err)
+		ret = err;
+
+	kfree(log);
+
+	if (ret < 0 && prog)
 		bpf_prog_put(prog);
 	return ret;
 }
@@ -6513,7 +6533,7 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 		err = bpf_map_do_batch(&attr, uattr.user, BPF_MAP_DELETE_BATCH);
 		break;
 	case BPF_LINK_CREATE:
-		err = link_create(&attr, uattr);
+		err = link_create(&attr, uattr, &attr_common, uattr_common, size_common);
 		break;
 	case BPF_LINK_UPDATE:
 		err = link_update(&attr);
-- 
2.55.0