bpftool: Fix regression of "bpftool cgroup tree" EINVAL on older kernels

If cgroup_has_attached_progs queries an attach type not supported
by the running kernel, due to the kernel being older than the bpftool
build, it would encounter an -EINVAL from BPF_PROG_QUERY syscall.

Prior to commit 98b303c ("bpftool: Query only cgroup-related
attach types"), this EINVAL would be ignored by the function, allowing
the function to only consider supported attach types. The commit
changed so that, instead of querying all attach types, only attach
types from the array `cgroup_attach_types` is queried. The assumption
is that because these are only cgroup attach types, they should all
be supported. Unfortunately this assumption may be false when the
kernel is older than the bpftool build, where the attach types queried
by bpftool is not yet implemented in the kernel. This would result in
errors such as:

  $ bpftool cgroup tree
  CgroupPath
  ID       AttachType      AttachFlags     Name
  Error: can't query bpf programs attached to /sys/fs/cgroup: Invalid argument

This patch restores the logic of ignoring EINVAL from prior to that patch.

Fixes: 98b303c ("bpftool: Query only cgroup-related attach types")
Reported-by: Sagarika Sharma <[email protected]>
Reported-by: Minh-Anh Nguyen <[email protected]>
Signed-off-by: YiFei Zhu <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Quentin Monnet <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: zhuyifei1999

tools/bpf/bpftool/cgroup.c

@@ -221,7 +221,7 @@ static int cgroup_has_attached_progs(int cgroup_fd)
 	for (i = 0; i < ARRAY_SIZE(cgroup_attach_types); i++) {
 		int count = count_attached_bpf_progs(cgroup_fd, cgroup_attach_types[i]);
 
-		if (count < 0)
+		if (count < 0 && errno != EINVAL)
 			return -1;
 
 		if (count > 0) {