[PATCH bpf v4 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. So let's remove the
AttachFlags field and the associated logic. After this patch, the
above effective cgroup tree will show as bellow:

$ bpftool cgroup tree /sys/fs/cgroup effective
CgroupPath
ID       AttachType      Name
/sys/fs/cgroup
6        cgroup_sysctl   sysctl_tcp_mem
13       cgroup_sysctl   sysctl_tcp_mem
/sys/fs/cgroup/cg1
20       cgroup_sysctl   sysctl_tcp_mem
6        cgroup_sysctl   sysctl_tcp_mem
13       cgroup_sysctl   sysctl_tcp_mem
/sys/fs/cgroup/cg1/cg2
20       cgroup_sysctl   sysctl_tcp_mem
6        cgroup_sysctl   sysctl_tcp_mem
13       cgroup_sysctl   sysctl_tcp_mem

Fixes: b79c9fc9551b ("bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP")
Fixes: a98bf57391a2 ("tools: bpftool: add support for reporting the effective cgroup progs")
Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
---
 tools/bpf/bpftool/cgroup.c | 54 ++++++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/cgroup.c b/tools/bpf/bpftool/cgroup.c
index cced668fb2a3..b46a998d8f8d 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)
@@ -195,6 +198,32 @@ static int cgroup_has_attached_progs(int cgroup_fd)
 
 	return no_prog ? 0 : 1;
 }
+
+static int show_effective_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
+				    int level)
+{
+	LIBBPF_OPTS(bpf_prog_query_opts, p);
+	__u32 prog_ids[1024] = {0};
+	__u32 iter;
+	int ret;
+
+	p.query_flags = query_flags;
+	p.prog_cnt = ARRAY_SIZE(prog_ids);
+	p.prog_ids = prog_ids;
+
+	ret = bpf_prog_query_opts(cgroup_fd, type, &p);
+	if (ret)
+		return ret;
+
+	if (p.prog_cnt == 0)
+		return 0;
+
+	for (iter = 0; iter < p.prog_cnt; iter++)
+		show_bpf_prog(prog_ids[iter], type, NULL, level);
+
+	return 0;
+}
+
 static int show_attached_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
 				   int level)
 {
@@ -245,6 +274,14 @@ static int show_attached_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
 	return 0;
 }
 
+static int show_bpf_progs(int cgroup_fd, enum bpf_attach_type type,
+			  int level)
+{
+	return query_flags & BPF_F_QUERY_EFFECTIVE ?
+	       show_effective_bpf_progs(cgroup_fd, type, level) :
+	       show_attached_bpf_progs(cgroup_fd, type, level);
+}
+
 static int do_show(int argc, char **argv)
 {
 	enum bpf_attach_type type;
@@ -292,6 +329,8 @@ 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");
@@ -304,7 +343,7 @@ static int do_show(int argc, char **argv)
 		 * If we were able to get the show for at least one
 		 * attach type, let's return 0.
 		 */
-		if (show_attached_bpf_progs(cgroup_fd, type, 0) == 0)
+		if (show_bpf_progs(cgroup_fd, type, 0) == 0)
 			ret = 0;
 	}
 
@@ -362,7 +401,7 @@ static int do_show_tree_fn(const char *fpath, const struct stat *sb,
 
 	btf_vmlinux = libbpf_find_kernel_btf();
 	for (type = 0; type < __MAX_BPF_ATTACH_TYPE; type++)
-		show_attached_bpf_progs(cgroup_fd, type, ftw->level);
+		show_bpf_progs(cgroup_fd, type, ftw->level);
 
 	if (errno == EINVAL)
 		/* Last attach type does not support query.
@@ -436,6 +475,11 @@ 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