[systemd-devel] [PATCH v3] Do not clear parent mount flags when setting up namespaces

[Topi Miettinen]

When setting up a namespace, flags like noexec, nosuid and nodev are
cleared, so the mounts always have exec, suid, dev flags enabled.

Copy parent directory mount flags when setting up a namespace and
don't accidentally clear mount flags later.
---
 src/core/namespace.c | 12 ++++++++++--
 src/shared/util.c    | 24 ++++++++++++++++++++++--
 src/shared/util.h    |  2 ++
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/core/namespace.c b/src/core/namespace.c
index 4b8dbdd..6807e0c 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -149,6 +149,7 @@ static int mount_dev(BindMount *m) {
         const char *d, *dev = NULL, *devpts = NULL, *devshm = NULL, *devhugepages = NULL, *devmqueue = NULL, *devlog = NULL, *devptmx = NULL;
         _cleanup_umask_ mode_t u;
         int r;
+        unsigned long parent_flags;
 
         assert(m);
 
@@ -159,7 +160,10 @@ static int mount_dev(BindMount *m) {
 
         dev = strappenda(temporary_mount, "/dev");
         (void)mkdir(dev, 0755);
-        if (mount("tmpfs", dev, "tmpfs", MS_NOSUID|MS_STRICTATIME, "mode=755") < 0) {
+        r = get_mount_flags("/dev", &parent_flags);
+        if (r < 0)
+                goto fail;
+        if (mount("tmpfs", dev, "tmpfs", parent_flags|MS_NOSUID|MS_STRICTATIME, "mode=755") < 0) {
                 r = -errno;
                 goto fail;
         }
@@ -272,6 +276,7 @@ static int mount_kdbus(BindMount *m) {
         char *busnode = NULL, *root;
         struct stat st;
         int r;
+        unsigned long parent_flags;
 
         assert(m);
 
@@ -282,7 +287,10 @@ static int mount_kdbus(BindMount *m) {
 
         root = strappenda(temporary_mount, "/kdbus");
         (void)mkdir(root, 0755);
-        if (mount("tmpfs", root, "tmpfs", MS_NOSUID|MS_STRICTATIME, "mode=777") < 0) {
+        r = get_mount_flags("/sys/fs/kdbus", &parent_flags);
+        if (r < 0)
+                goto fail;
+        if (mount("tmpfs", root, "tmpfs", parent_flags|MS_NOSUID|MS_STRICTATIME, "mode=777") < 0) {
                 r = -errno;
                 goto fail;
         }
diff --git a/src/shared/util.c b/src/shared/util.c
index dfaf7f7..b28213f 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -61,6 +61,7 @@
 #include <sys/personality.h>
 #include <sys/xattr.h>
 #include <libgen.h>
+#include <sys/statvfs.h>
 #undef basename
 
 #ifdef HAVE_SYS_AUXV_H
@@ -6858,6 +6859,16 @@ int umount_recursive(const char *prefix, int flags) {
         return r ? r : n;
 }
 
+int get_mount_flags(const char *path, unsigned long *flags) {
+        struct statvfs buf;
+
+        if (statvfs(path, &buf) < 0)
+                return -errno;
+
+        *flags = buf.f_flag;
+        return 0;
+}
+
 int bind_remount_recursive(const char *prefix, bool ro) {
         _cleanup_set_free_free_ Set *done = NULL;
         _cleanup_free_ char *cleaned = NULL;
@@ -6892,6 +6903,7 @@ int bind_remount_recursive(const char *prefix, bool ro) {
                 _cleanup_set_free_free_ Set *todo = NULL;
                 bool top_autofs = false;
                 char *x;
+                unsigned long orig_flags;
 
                 todo = set_new(&string_hash_ops);
                 if (!todo)
@@ -6969,7 +6981,11 @@ int bind_remount_recursive(const char *prefix, bool ro) {
                         if (mount(cleaned, cleaned, NULL, MS_BIND|MS_REC, NULL) < 0)
                                 return -errno;
 
-                        if (mount(NULL, prefix, NULL, MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)
+                        r = get_mount_flags(prefix, &orig_flags);
+                        if (r < 0)
+                                return r;
+                        orig_flags &= ~MS_RDONLY;
+                        if (mount(NULL, prefix, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)
                                 return -errno;
 
                         x = strdup(cleaned);
@@ -6989,7 +7005,11 @@ int bind_remount_recursive(const char *prefix, bool ro) {
                         if (r < 0)
                                 return r;
 
-                        if (mount(NULL, x, NULL, MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) {
+                        r = get_mount_flags(x, &orig_flags);
+                        if (r < 0)
+                                return r;
+                        orig_flags &= ~MS_RDONLY;
+                        if (mount(NULL, x, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) {
 
                                 /* Deal with mount points that are
                                  * obstructed by a later mount */
diff --git a/src/shared/util.h b/src/shared/util.h
index a131a3c..d5aa988 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -1021,6 +1021,8 @@ union file_handle_union {
 
 int update_reboot_param_file(const char *param);
 
+int get_mount_flags(const char *path, unsigned long *flags);
+
 int umount_recursive(const char *target, int flags);
 
 int bind_remount_recursive(const char *prefix, bool ro);
-- 
2.1.4