Merge pull request #21241 from wat-ze-hex/2021-11-04-fix-bpf-foreign-realization

core, bpf: fix bpf-foreign cgroup controller realization

src/core/bpf-foreign.c

@@ -4,8 +4,10 @@
 #include "bpf-program.h"
 #include "cgroup.h"
 #include "memory-util.h"
+#include "missing_magic.h"
 #include "mountpoint-util.h"
 #include "set.h"
+#include "stat-util.h"
 
 typedef struct BPFForeignKey BPFForeignKey;
 struct BPFForeignKey {
@@ -84,6 +86,14 @@ static int bpf_foreign_prepare(
         assert(u);
         assert(bpffs_path);
 
+        r = path_is_fs_type(bpffs_path, BPF_FS_MAGIC);
+        if (r < 0)
+                return log_unit_error_errno(u, r,
+                                "Failed to determine filesystem type of %s: %m", bpffs_path);
+        if (r == 0)
+                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
+                                "Path in BPF filesystem is expected.");
+
         r = bpf_program_new_from_bpffs_path(bpffs_path, &prog);
         if (r < 0)
                 return log_unit_error_errno(u, r, "Failed to create foreign BPFProgram: %m");
@@ -111,16 +121,6 @@ static int bpf_foreign_prepare(
         return 0;
 }
 
-int bpf_foreign_supported(void) {
-        int r;
-
-        r = cg_all_unified();
-        if (r <= 0)
-                return r;
-
-        return path_is_mount_point("/sys/fs/bpf", NULL, 0);
-}
-
 int bpf_foreign_install(Unit *u) {
         _cleanup_free_ char *cgroup_path = NULL;
         CGroupBPFForeignProgram *p;

src/core/bpf-foreign.h

@@ -4,7 +4,10 @@
 
 #include "unit.h"
 
-int bpf_foreign_supported(void);
+static inline int bpf_foreign_supported(void) {
+        return cg_all_unified();
+}
+
 /*
  * Attach cgroup-bpf programs foreign to systemd, i.e. loaded to the kernel by an entity
  * external to systemd.