core: Make unprivileged case ignore ownership, add "_compose" context

I was in the process of trying to support `%post` scripts, and I
wanted to use `rpm-ostree container` for convenient and safe testing.
However the recent package layering changes broke it to error out
on perms like `filesystem`'s `root:mail` on `/var/mail`.

I decided to introduce a new `rpmostree_context_new_compose` which had
the current behavior, switch `compose tree` to use it, and then change
`_new_unprivileged` to *really* be unprivileged.  Specifically we
ignore file ownership (and fix dir owners) because we assume we'll be
operating with `bare-user` repos.

Closes: #327
Approved by: jlebon

src/app/rpmostree-compose-builtin-tree.c

@@ -689,7 +689,7 @@ rpmostree_compose_builtin_tree (int             argc,
       goto out;
     }
 
-  corectx = rpmostree_context_new_unprivileged (self->cachedir_dfd, cancellable, error);
+  corectx = rpmostree_context_new_compose (self->cachedir_dfd, cancellable, error);
   if (!corectx)
     goto out;
 

src/libpriv/rpmostree-core.c

@@ -275,6 +275,7 @@ struct _RpmOstreeContext {
   RpmOstreeTreespec *spec;
   HifContext *hifctx;
   OstreeRepo *ostreerepo;
+  gboolean unprivileged;
   char *dummy_instroot_path;
   OstreeSePolicy *sepolicy;
 };
@@ -356,10 +357,11 @@ rpmostree_context_new_system (GCancellable *cancellable,
   return self;
 }
 
-RpmOstreeContext *
-rpmostree_context_new_unprivileged (int           userroot_dfd,
-                                     GCancellable *cancellable,
-                                     GError      **error)
+static RpmOstreeContext *
+rpmostree_context_new_internal (int           userroot_dfd,
+                                gboolean      unprivileged,
+                                GCancellable *cancellable,
+                                GError      **error)
 {
   g_autoptr(RpmOstreeContext) ret = rpmostree_context_new_system (cancellable, error);
   struct stat stbuf;
@@ -367,6 +369,8 @@ rpmostree_context_new_unprivileged (int           userroot_dfd,
   if (!ret)
     goto out;
 
+  ret->unprivileged = unprivileged;
+
   { g_autofree char *reposdir = glnx_fdrel_abspath (userroot_dfd, "rpmmd.repos.d");
     hif_context_set_repo_dir (ret->hifctx, reposdir);
   }
@@ -408,6 +412,22 @@ rpmostree_context_new_unprivileged (int           userroot_dfd,
   return NULL;
 }
 
+RpmOstreeContext *
+rpmostree_context_new_compose (int basedir_dfd,
+                               GCancellable *cancellable,
+                               GError **error)
+{
+  return rpmostree_context_new_internal (basedir_dfd, FALSE, cancellable, error);
+}
+
+RpmOstreeContext *
+rpmostree_context_new_unprivileged (int basedir_dfd,
+                                    GCancellable *cancellable,
+                                    GError **error)
+{
+  return rpmostree_context_new_internal (basedir_dfd, TRUE, cancellable, error);
+}
+
 /* XXX: or put this in new_system() instead? */
 void
 rpmostree_context_set_repo (RpmOstreeContext *self,
@@ -1290,7 +1310,7 @@ rpmostree_context_download (RpmOstreeContext *ctx,
 }
 
 static gboolean
-import_one_package (OstreeRepo     *ostreerepo,
+import_one_package (RpmOstreeContext *self,
                     HifContext     *hifctx,
                     HifPackage     *pkg,
                     OstreeSePolicy *sepolicy,
@@ -1298,6 +1318,7 @@ import_one_package (OstreeRepo     *ostreerepo,
                     GError        **error)
 {
   gboolean ret = FALSE;
+  OstreeRepo *ostreerepo = self->ostreerepo;
   g_autofree char *ostree_commit = NULL;
   glnx_unref_object RpmOstreeUnpacker *unpacker = NULL;
   g_autofree char *pkg_path;
@@ -1314,6 +1335,8 @@ import_one_package (OstreeRepo     *ostreerepo,
     }
 
   flags = RPMOSTREE_UNPACKER_FLAGS_OSTREE_CONVENTION;
+  if (self->unprivileged)
+    flags |= RPMOSTREE_UNPACKER_FLAGS_UNPRIVILEGED;
 
   /* TODO - tweak the unpacker flags for containers */
   unpacker = rpmostree_unpacker_new_at (AT_FDCWD, pkg_path, flags, error);
@@ -1369,7 +1392,7 @@ rpmostree_context_import (RpmOstreeContext *self,
     for (guint i = 0; i < install->packages_to_import->len; i++)
       {
         HifPackage *pkg = install->packages_to_import->pdata[i];
-        if (!import_one_package (self->ostreerepo, hifctx, pkg,
+        if (!import_one_package (self, hifctx, pkg,
                                  self->sepolicy, cancellable, error))
           goto out;
         hif_state_assert_done (hifstate);

src/libpriv/rpmostree-core.h

@@ -38,6 +38,10 @@ G_DECLARE_FINAL_TYPE (RpmOstreeInstall, rpmostree_install, RPMOSTREE, INSTALL, G
 RpmOstreeContext *rpmostree_context_new_system (GCancellable *cancellable,
                                                 GError **error);
 
+RpmOstreeContext *rpmostree_context_new_compose (int basedir_dfd,
+                                                 GCancellable *cancellable,
+                                                 GError **error);
+
 RpmOstreeContext *rpmostree_context_new_unprivileged (int basedir_dfd,
                                                       GCancellable *cancellable,
                                                       GError **error);

src/libpriv/rpmostree-unpacker.c

@@ -503,15 +503,15 @@ typedef struct
 } cb_data;
 
 static OstreeRepoCommitFilterResult
-filter_cb (OstreeRepo         *repo,
-           const char         *path,
-           GFileInfo          *file_info,
-           gpointer            user_data)
+compose_filter_cb (OstreeRepo         *repo,
+                   const char         *path,
+                   GFileInfo          *file_info,
+                   gpointer            user_data)
 {
   RpmOstreeUnpacker *self = ((cb_data*)user_data)->self;
   GError **error = ((cb_data*)user_data)->error;
 
-  /* For now we fail if an RPM requires a file to be owned by non-root. The
+  /* In the system case, fail if an RPM requires a file to be owned by non-root. The
    * problem is that RPM provides strings, but ostree records uids/gids. Any
    * mapping we choose would be specific to a certain userdb and thus not
    * portable. To properly support this will probably require switching over to
@@ -548,6 +548,23 @@ filter_cb (OstreeRepo         *repo,
   return OSTREE_REPO_COMMIT_FILTER_ALLOW;
 }
 
+static OstreeRepoCommitFilterResult
+unprivileged_filter_cb (OstreeRepo         *repo,
+                        const char         *path,
+                        GFileInfo          *file_info,
+                        gpointer            user_data)
+{
+  guint32 mode = g_file_info_get_attribute_uint32 (file_info, "unix::mode");
+  /* Fedora changed the directories to not be writable by root for bad
+   * reasons, which isn't useful here since we expect people to slap a
+   * ro bind mount on top, so let's just mark as writable by user.
+   */
+  if (g_file_info_get_file_type (file_info) == G_FILE_TYPE_DIRECTORY)
+    mode |= S_IWUSR;
+  g_file_info_set_attribute_uint32 (file_info, "unix::mode", mode);
+  return OSTREE_REPO_COMMIT_FILTER_ALLOW;
+}
+
 static GVariant*
 xattr_cb (OstreeRepo  *repo,
           const char  *path,
@@ -596,8 +613,14 @@ import_rpm_to_repo (RpmOstreeUnpacker *self,
 
   GError *cb_error = NULL;
   cb_data fdata = { self, &cb_error };
+  OstreeRepoCommitFilter filter;
 
-  modifier = ostree_repo_commit_modifier_new (0, filter_cb, &fdata, NULL);
+  if ((self->flags & RPMOSTREE_UNPACKER_FLAGS_UNPRIVILEGED) > 0)
+    filter = unprivileged_filter_cb;
+  else
+    filter = compose_filter_cb;
+
+  modifier = ostree_repo_commit_modifier_new (0, filter, &fdata, NULL);
   ostree_repo_commit_modifier_set_xattr_callback (modifier, xattr_cb,
                                                   NULL, self);
   ostree_repo_commit_modifier_set_sepolicy (modifier, sepolicy);

src/libpriv/rpmostree-unpacker.h

@@ -36,9 +36,11 @@ GType rpmostree_unpacker_get_type (void);
 /**
  * RpmOstreeUnpackerFlags:
  * @RPMOSTREE_UNPACKER_FLAGS_OSTREE_CONVENTION: Move files to follow ostree convention
+ * @RPMOSTREE_UNPACKER_FLAGS_UNPRIVILEGED: Ignore file ownership and setuid modes
  */
 typedef enum {
-  RPMOSTREE_UNPACKER_FLAGS_OSTREE_CONVENTION =  (1 << 0)
+  RPMOSTREE_UNPACKER_FLAGS_OSTREE_CONVENTION =  (1 << 0),
+  RPMOSTREE_UNPACKER_FLAGS_UNPRIVILEGED =  (1 << 1)
 } RpmOstreeUnpackerFlags;
 
 RpmOstreeUnpacker*