[PATCH bpf-next v3 2/2] bpftool: Fix wrong cgroup attach flags being assigned to effective progs

[Pu Lehui]

From: Pu Lehui <pulehui@xxxxxxxxxx>

When root-cgroup attach multi progs and sub-cgroup attach a override prog,
bpftool will display incorrectly for the attach flags of the sub-cgroup’s
effective progs:

$ bpftool cgroup tree /sys/fs/cgroup effective
CgroupPath
ID       AttachType      AttachFlags     Name
/sys/fs/cgroup
6        cgroup_sysctl   multi           sysctl_tcp_mem
13       cgroup_sysctl   multi           sysctl_tcp_mem
/sys/fs/cgroup/cg1
20       cgroup_sysctl   override        sysctl_tcp_mem
6        cgroup_sysctl   override        sysctl_tcp_mem <- wrong
13       cgroup_sysctl   override        sysctl_tcp_mem <- wrong
/sys/fs/cgroup/cg1/cg2
20       cgroup_sysctl                   sysctl_tcp_mem
6        cgroup_sysctl                   sysctl_tcp_mem
13       cgroup_sysctl                   sysctl_tcp_mem

Attach flags is only valid for attached progs of this layer cgroup,
but not for effective progs. For querying with EFFECTIVE flags,
exporting attach flags does not make sense. Since prog_attach_flags
array not being populated when effective query, so we can just remove
the corresponding attach flags logic.

Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
---
 tools/bpf/bpftool/cgroup.c | 54 +++++++++++++++++++++++---------------
 1 file changed, 33 insertions(+), 21 deletions(-)

diff --git a/tools/bpf/bpftool/cgroup.c b/tools/bpf/bpftool/cgroup.c
index cced668fb2a3..24cdb0b41f89 100644
--- a/tools/bpf/bpftool/cgroup.c
+++ b/tools/bpf/bpftool/cgroup.c
@@ -136,8 +136,8 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 			jsonw_string_field(json_wtr, "attach_type", attach_type_str);
 		else
 			jsonw_uint_field(json_wtr, "attach_type", attach_type);
-		jsonw_string_field(json_wtr, "attach_flags",
-				   attach_flags_str);
+		if (!(query_flags & BPF_F_QUERY_EFFECTIVE))
+			jsonw_string_field(json_wtr, "attach_flags", attach_flags_str);
 		jsonw_string_field(json_wtr, "name", prog_name);
 		if (attach_btf_name)
 			jsonw_string_field(json_wtr, "attach_btf_name", attach_btf_name);
@@ -150,7 +150,10 @@ static int show_bpf_prog(int id, enum bpf_attach_type attach_type,
 			printf("%-15s", attach_type_str);
 		else
 			printf("type %-10u", attach_type);
-		printf(" %-15s %-15s", attach_flags_str, prog_name);
+		if (query_flags & BPF_F_QUERY_EFFECTIVE)
+			printf(" %-15s", prog_name);
+		else
+			printf(" %-15s %-15s", attach_flags_str, prog_name);
 		if (attach_btf_name)
 			printf(" %-15s", attach_btf_name);
 		else if (info.attach_btf_id)
@@ -200,7 +203,7 @@ static int show_attached_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
 {
 	LIBBPF_OPTS(bpf_prog_query_opts, p);
 	__u32 prog_attach_flags[1024] = {0};
-	const char *attach_flags_str;
+	const char *attach_flags_str = NULL;
 	__u32 prog_ids[1024] = {0};
 	char buf[32];
 	__u32 iter;
@@ -219,23 +222,25 @@ static int show_attached_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
 		return 0;
 
 	for (iter = 0; iter < p.prog_cnt; iter++) {
-		__u32 attach_flags;
-
-		attach_flags = prog_attach_flags[iter] ?: p.attach_flags;
-
-		switch (attach_flags) {
-		case BPF_F_ALLOW_MULTI:
-			attach_flags_str = "multi";
-			break;
-		case BPF_F_ALLOW_OVERRIDE:
-			attach_flags_str = "override";
-			break;
-		case 0:
-			attach_flags_str = "";
-			break;
-		default:
-			snprintf(buf, sizeof(buf), "unknown(%x)", attach_flags);
-			attach_flags_str = buf;
+		if (!(query_flags & BPF_F_QUERY_EFFECTIVE)) {
+			__u32 attach_flags;
+
+			attach_flags = prog_attach_flags[iter] ?: p.attach_flags;
+
+			switch (attach_flags) {
+			case BPF_F_ALLOW_MULTI:
+				attach_flags_str = "multi";
+				break;
+			case BPF_F_ALLOW_OVERRIDE:
+				attach_flags_str = "override";
+				break;
+			case 0:
+				attach_flags_str = "";
+				break;
+			default:
+				snprintf(buf, sizeof(buf), "unknown(%x)", attach_flags);
+				attach_flags_str = buf;
+			}
 		}
 
 		show_bpf_prog(prog_ids[iter], type,
@@ -292,6 +297,8 @@ static int do_show(int argc, char **argv)
 
 	if (json_output)
 		jsonw_start_array(json_wtr);
+	else if (query_flags & BPF_F_QUERY_EFFECTIVE)
+		printf("%-8s %-15s %-15s\n", "ID", "AttachType", "Name");
 	else
 		printf("%-8s %-15s %-15s %-15s\n", "ID", "AttachType",
 		       "AttachFlags", "Name");
@@ -436,6 +443,11 @@ static int do_show_tree(int argc, char **argv)
 
 	if (json_output)
 		jsonw_start_array(json_wtr);
+	else if (query_flags & BPF_F_QUERY_EFFECTIVE)
+		printf("%s\n"
+		       "%-8s %-15s %-15s\n",
+		       "CgroupPath",
+		       "ID", "AttachType", "Name");
 	else
 		printf("%s\n"
 		       "%-8s %-15s %-15s %-15s\n",
-- 
2.25.1