Systemd v254 LSM stacking issue - patch

[Casey Schaufler]

Systemd version 254 (included in Fedora 39) has an assertion that
only one of Smack and SELinux is active. This can make experimenting
with full LSM stacking frustrating. This patch adds multiple label
operation support and removes the pesky assertion. It's experimental.

---
 src/basic/label.c       | 48 ++++++++++++++++++++++++++++++++++--------------
 src/core/smack-setup.c  |  2 +-
 src/shared/label-util.c |  2 --
 src/shared/smack-util.c |  2 +-
 4 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/src/basic/label.c b/src/basic/label.c
index f134e77589..6827fbbd46 100644
--- a/src/basic/label.c
+++ b/src/basic/label.c
@@ -5,26 +5,46 @@
 
 #include "label.h"
 
-static const LabelOps *label_ops = NULL;
+#define POSSIBLE_LABEL_OPS 2 /* SELinux and Smack */
 
-int label_ops_set(const LabelOps *ops) {
-        if (label_ops)
-                return -EBUSY;
+static const LabelOps *label_ops[POSSIBLE_LABEL_OPS];
 
-        label_ops = ops;
-        return 0;
+int label_ops_set(const LabelOps *ops) {
+        int i;
+
+        for (i = 0; i < POSSIBLE_LABEL_OPS; i++) {
+                if (!label_ops[i]) {
+                        label_ops[i] = ops;
+                        return 0;
+                }
+        }
+        return -EBUSY;
 }
 
 int label_ops_pre(int dir_fd, const char *path, mode_t mode) {
-        if (!label_ops || !label_ops->pre)
-                return 0;
-
-        return label_ops->pre(dir_fd, path, mode);
+        int i;
+        int r;
+
+        for (i = 0; i < POSSIBLE_LABEL_OPS; i++) {
+                if (label_ops[i] && label_ops[i]->pre) {
+                        r = label_ops[i]->pre(dir_fd, path, mode);
+                        if (r)
+                                return r;
+                }
+        }
+        return 0;
 }
 
 int label_ops_post(int dir_fd, const char *path) {
-        if (!label_ops || !label_ops->post)
-                return 0;
-
-        return label_ops->post(dir_fd, path);
+        int i;
+        int r;
+
+        for (i = 0; i < POSSIBLE_LABEL_OPS; i++) {
+                if (label_ops[i] && label_ops[i]->post) {
+                        r = label_ops[i]->post(dir_fd, path);
+                        if (r)
+                                return r;
+                }
+        }
+        return 0;
 }
diff --git a/src/core/smack-setup.c b/src/core/smack-setup.c
index bcaa237c8d..b1dbbbc2e8 100644
--- a/src/core/smack-setup.c
+++ b/src/core/smack-setup.c
@@ -319,7 +319,7 @@ int mac_smack_setup(bool *loaded_policy) {
         }
 
 #if HAVE_SMACK_RUN_LABEL
-        r = write_string_file("/proc/self/attr/current", SMACK_RUN_LABEL, WRITE_STRING_FILE_DISABLE_BUFFER);
+        r = write_string_file("/proc/self/attr/smack/current", SMACK_RUN_LABEL, WRITE_STRING_FILE_DISABLE_BUFFER);
         if (r < 0)
                 log_warning_errno(r, "Failed to set SMACK label \"" SMACK_RUN_LABEL "\" on self: %m");
         r = write_string_file("/sys/fs/smackfs/ambient", SMACK_RUN_LABEL, WRITE_STRING_FILE_DISABLE_BUFFER);
diff --git a/src/shared/label-util.c b/src/shared/label-util.c
index 3316c9ed37..3154818371 100644
--- a/src/shared/label-util.c
+++ b/src/shared/label-util.c
@@ -120,8 +120,6 @@ int btrfs_subvol_make_label(const char *path) {
 int mac_init(void) {
         int r;
 
-        assert(!(mac_selinux_use() && mac_smack_use()));
-
         r = mac_selinux_init();
         if (r < 0)
                 return r;
diff --git a/src/shared/smack-util.c b/src/shared/smack-util.c
index 1f88e724d0..5661428f96 100644
--- a/src/shared/smack-util.c
+++ b/src/shared/smack-util.c
@@ -112,7 +112,7 @@ int mac_smack_apply_pid(pid_t pid, const char *label) {
         if (!mac_smack_use())
                 return 0;
 
-        p = procfs_file_alloca(pid, "attr/current");
+        p = procfs_file_alloca(pid, "attr/smack/current");
         r = write_string_file(p, label, WRITE_STRING_FILE_DISABLE_BUFFER);
         if (r < 0)
                 return r;