[PATCH bpf-next v2 3/9] bpf: Add log support for iter link_create

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

iter BPF_LINK_CREATE returns an error without explaining invalid target
FDs, flags, or iterator information, or an unsupported program.

Pass the BPF_LINK_CREATE log to the iter attach path and report these
failures.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/linux/bpf.h   |  3 ++-
 kernel/bpf/bpf_iter.c | 27 +++++++++++++++++++++------
 kernel/bpf/syscall.c  |  2 +-
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 36587b63ce13..c3f6364bc1d8 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3276,7 +3276,8 @@ void bpf_iter_unreg_target(const struct bpf_iter_reg *reg_info);
 int bpf_iter_prog_supported(struct bpf_prog *prog);
 const struct bpf_func_proto *
 bpf_iter_get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog);
-int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr, struct bpf_prog *prog);
+int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr, struct bpf_prog *prog,
+			 struct bpf_verifier_log *log);
 int bpf_iter_new_fd(struct bpf_link *link);
 bool bpf_link_is_iter(struct bpf_link *link);
 struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop);
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index f0b29a170935..4a9e08fb8e75 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -5,6 +5,7 @@
 #include <linux/anon_inodes.h>
 #include <linux/filter.h>
 #include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
 #include <linux/rcupdate_trace.h>
 
 struct bpf_iter_target_info {
@@ -528,7 +529,7 @@ bool bpf_link_is_iter(struct bpf_link *link)
 }
 
 int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr,
-			 struct bpf_prog *prog)
+			 struct bpf_prog *prog, struct bpf_verifier_log *log)
 {
 	struct bpf_iter_target_info *tinfo = NULL, *iter;
 	struct bpf_link_primer link_primer;
@@ -538,24 +539,36 @@ int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr,
 	bpfptr_t ulinfo;
 	int err;
 
-	if (attr->link_create.target_fd || attr->link_create.flags)
+	if (attr->link_create.target_fd) {
+		bpf_log(log, "Invalid target_fd.\n");
+		return -EINVAL;
+	}
+	if (attr->link_create.flags) {
+		bpf_log(log, "Invalid flags.\n");
 		return -EINVAL;
+	}
 
 	memset(&linfo, 0, sizeof(union bpf_iter_link_info));
 
 	ulinfo = make_bpfptr(attr->link_create.iter_info, uattr.is_kernel);
 	linfo_len = attr->link_create.iter_info_len;
-	if (bpfptr_is_null(ulinfo) ^ !linfo_len)
+	if (bpfptr_is_null(ulinfo) ^ !linfo_len) {
+		bpf_log(log, "iter_info and iter_info_len must be both set or both unset.\n");
 		return -EINVAL;
+	}
 
 	if (!bpfptr_is_null(ulinfo)) {
 		err = bpf_check_uarg_tail_zero(ulinfo, sizeof(linfo),
 					       linfo_len);
-		if (err)
+		if (err) {
+			bpf_log(log, "Invalid iter_info_len.\n");
 			return err;
+		}
 		linfo_len = min_t(u32, linfo_len, sizeof(linfo));
-		if (copy_from_bpfptr(&linfo, ulinfo, linfo_len))
+		if (copy_from_bpfptr(&linfo, ulinfo, linfo_len)) {
+			bpf_log(log, "Invalid iter_info.\n");
 			return -EFAULT;
+		}
 	}
 
 	prog_btf_id = prog->aux->attach_btf_id;
@@ -570,8 +583,10 @@ int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr,
 	if (!tinfo)
 		return -ENOENT;
 
-	if (!bpf_iter_target_support_prog(tinfo, prog))
+	if (!bpf_iter_target_support_prog(tinfo, prog)) {
+		bpf_log(log, "The iter target does not support the bpf prog.\n");
 		return -EINVAL;
+	}
 
 	link = kzalloc_obj(*link, GFP_USER | __GFP_NOWARN);
 	if (!link)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 3c7bedced354..9627dfc982ff 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5929,7 +5929,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 			ret = bpf_raw_tp_link_attach(prog, NULL, attr->link_create.tracing.cookie,
 						     attr->link_create.attach_type);
 		else if (prog->expected_attach_type == BPF_TRACE_ITER)
-			ret = bpf_iter_link_attach(attr, uattr, prog);
+			ret = bpf_iter_link_attach(attr, uattr, prog, log);
 		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))
-- 
2.55.0