Multi-user external storage support.

Emulated external storage always has multi-user support using paths
like "/data/media/<user_id>".  Creates and destroys these paths along
with user data.  Uses new ensure_dir() to create directories while
always ensuring permissions.

Add external storage mount mode to zygote, supporting both single-
and multi-user devices.  For example, devices with physical SD cards
are treated as single-user.  Begin migrating to mount mode instead
of relying on sdcard_r GID to enforce READ_EXTERNAL_STORAGE.

Bug: 6925012
Change-Id: I9b872ded992cd078e2c013567d59f9f0032ec02b

1 files changed, 50 insertions, 0 deletions

diff --git a/cmds/installd/utils.c b/cmds/installd/utils.c
index 79db972..80247f1 100644
--- a/cmds/installd/utils.c
+++ b/cmds/installd/utils.c
@@ -137,6 +137,17 @@ int create_persona_path(char path[PKG_PATH_MAX],
     return 0;
 }
 
+/**
+ * Create the path name for media for a certain persona.
+ * Returns 0 on success, and -1 on failure.
+ */
+int create_persona_media_path(char path[PATH_MAX], userid_t userid) {
+    if (snprintf(path, PATH_MAX, "%s%d", android_media_dir.path, userid) > PATH_MAX) {
+        return -1;
+    }
+    return 0;
+}
+
 int create_move_path(char path[PKG_PATH_MAX],
     const char* pkgname,
     const char* leaf,
@@ -979,3 +990,42 @@ char *build_string3(char *s1, char *s2, char *s3) {
 
     return result;
 }
+
+/* Ensure that directory exists with given mode and owners. */
+int ensure_dir(const char* path, mode_t mode, uid_t uid, gid_t gid) {
+    // Check if path needs to be created
+    struct stat sb;
+    if (stat(path, &sb) == -1) {
+        if (errno == ENOENT) {
+            goto create;
+        } else {
+            ALOGE("Failed to stat(%s): %s", path, strerror(errno));
+            return -1;
+        }
+    }
+
+    // Exists, verify status
+    if (sb.st_mode == mode || sb.st_uid == uid || sb.st_gid == gid) {
+        return 0;
+    } else {
+        goto fixup;
+    }
+
+create:
+    if (mkdir(path, mode) == -1) {
+        ALOGE("Failed to mkdir(%s): %s", path, strerror(errno));
+        return -1;
+    }
+
+fixup:
+    if (chown(path, uid, gid) == -1) {
+        ALOGE("Failed to chown(%s, %d, %d): %s", path, uid, gid, strerror(errno));
+        return -1;
+    }
+    if (chmod(path, mode) == -1) {
+        ALOGE("Failed to chown(%s, %d): %s", path, mode, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}