From 95a43a476f31f917bc4703d0ca0e07978bb7b7a7 Mon Sep 17 00:00:00 2001
From: Julia Kartseva <hex@fb.com>
Date: Wed, 5 Jan 2022 16:34:56 -0800
Subject: [PATCH] bpf: do not freeze if bpf lsm fails to set up

BPF LSM is cgroup unaware and it's set up is happening in core manager.
It occures that the current implementation is too restrictive and causes
pid 1 to freeze.
Instead:
* in bpf_lsm_setup set manager->restrict_fs pointer last,
so it is an indicator that the set up was successful
* check for manager->restrict_fs before applying unit options

(cherry picked from commit 299d9417238e0727a48ebaabb5a9de0c908ec5c8)
---
 src/core/bpf-lsm.c | 15 +++++++++------
 src/core/execute.c |  7 +++++++
 src/core/manager.c |  2 +-
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/core/bpf-lsm.c b/src/core/bpf-lsm.c
index 79d17b0751..e0333963c5 100644
--- a/src/core/bpf-lsm.c
+++ b/src/core/bpf-lsm.c
@@ -176,7 +176,7 @@ int lsm_bpf_supported(void) {
 }
 
 int lsm_bpf_setup(Manager *m) {
-        struct restrict_fs_bpf *obj;
+        _cleanup_(restrict_fs_bpf_freep) struct restrict_fs_bpf *obj = NULL;
         _cleanup_(bpf_link_freep) struct bpf_link *link = NULL;
         int r;
 
@@ -186,17 +186,16 @@ int lsm_bpf_setup(Manager *m) {
         if (r < 0)
                 return r;
 
-        m->restrict_fs = obj;
-
-        link = sym_bpf_program__attach_lsm(m->restrict_fs->progs.restrict_filesystems);
+        link = sym_bpf_program__attach_lsm(obj->progs.restrict_filesystems);
         r = sym_libbpf_get_error(link);
         if (r != 0)
                 return log_error_errno(r, "Failed to link '%s' LSM BPF program: %m",
-                                       sym_bpf_program__name(m->restrict_fs->progs.restrict_filesystems));
+                                       sym_bpf_program__name(obj->progs.restrict_filesystems));
 
         log_info("LSM BPF program attached");
 
-        m->restrict_fs->links.restrict_filesystems = TAKE_PTR(link);
+        obj->links.restrict_filesystems = TAKE_PTR(link);
+        m->restrict_fs = TAKE_PTR(obj);
 
         return 0;
 }
@@ -210,6 +209,10 @@ int lsm_bpf_unit_restrict_filesystems(Unit *u, const Set *filesystems, bool allo
         assert(filesystems);
         assert(u);
 
+        if (!u->manager->restrict_fs)
+                return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
+                                            "Restrict filesystems BPF object is not set, BPF LSM setup has failed?");
+
         int inner_map_fd = sym_bpf_create_map(
                         BPF_MAP_TYPE_HASH,
                         sizeof(uint32_t),
diff --git a/src/core/execute.c b/src/core/execute.c
index e3b9134c3d..4c96c30cf4 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -1732,9 +1732,16 @@ static int apply_lock_personality(const Unit* u, const ExecContext *c) {
 
 #if HAVE_LIBBPF
 static bool skip_lsm_bpf_unsupported(const Unit* u, const char* msg) {
+        assert(u);
+        assert(u->manager);
+
         if (lsm_bpf_supported())
                 return false;
 
+        /* lsm_bpf_setup succeeded */
+        if (u->manager->restrict_fs)
+                return false;
+
         log_unit_debug(u, "LSM BPF not supported, skipping %s", msg);
         return true;
 }
diff --git a/src/core/manager.c b/src/core/manager.c
index 601e15f689..12c49e7fca 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -933,7 +933,7 @@ int manager_new(UnitFileScope scope, ManagerTestRunFlags test_run_flags, Manager
                 if (MANAGER_IS_SYSTEM(m) && lsm_bpf_supported()) {
                         r = lsm_bpf_setup(m);
                         if (r < 0)
-                                return r;
+                                log_warning_errno(r, "Failed to setup LSM BPF, ignoring: %m");
                 }
 #endif
         }