Add derive_gid flag for mounting sdcardfs

Turns on the derive_gid feature for sdcardfs. This was moved
under a mount flag in the kernel.

Test: If the derive_gid flag is supported, the first mount
      should succeed. If the flag is not, the second should
      succeed.
Bug: 63245673
Change-Id: If1c1bce13d14120732e420252cb5605d33ce7c40

1 files changed, 40 insertions, 20 deletions

diff --git a/sdcard/sdcard.cpp b/sdcard/sdcard.cpp
index 343a90356..77d5a91f1 100644
--- a/sdcard/sdcard.cpp
+++ b/sdcard/sdcard.cpp
@@ -319,17 +319,31 @@ static void run(const char* source_path, const char* label, uid_t uid,
     LOG(FATAL) << "terminated prematurely";
 }
 
-static bool sdcardfs_setup(const std::string& source_path, const std::string& dest_path, uid_t fsuid,
-                        gid_t fsgid, bool multi_user, userid_t userid, gid_t gid, mode_t mask) {
-    std::string opts = android::base::StringPrintf("fsuid=%d,fsgid=%d,%smask=%d,userid=%d,gid=%d",
-            fsuid, fsgid, multi_user?"multiuser,":"", mask, userid, gid);
+static bool sdcardfs_setup(const std::string& source_path, const std::string& dest_path,
+                           uid_t fsuid, gid_t fsgid, bool multi_user, userid_t userid, gid_t gid,
+                           mode_t mask, bool derive_gid) {
+    std::string opts = android::base::StringPrintf(
+        "fsuid=%d,fsgid=%d,%s%smask=%d,userid=%d,gid=%d", fsuid, fsgid,
+        multi_user ? "multiuser," : "", derive_gid ? "derive_gid," : "", mask, userid, gid);
 
     if (mount(source_path.c_str(), dest_path.c_str(), "sdcardfs",
               MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts.c_str()) == -1) {
-        PLOG(ERROR) << "failed to mount sdcardfs filesystem";
-        return false;
+        if (derive_gid) {
+            PLOG(ERROR) << "trying to mount sdcardfs filesystem without derive_gid";
+            /* Maybe this isn't supported on this kernel. Try without. */
+            opts = android::base::StringPrintf("fsuid=%d,fsgid=%d,%smask=%d,userid=%d,gid=%d",
+                                               fsuid, fsgid, multi_user ? "multiuser," : "", mask,
+                                               userid, gid);
+            if (mount(source_path.c_str(), dest_path.c_str(), "sdcardfs",
+                      MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts.c_str()) == -1) {
+                PLOG(ERROR) << "failed to mount sdcardfs filesystem";
+                return false;
+            }
+        } else {
+            PLOG(ERROR) << "failed to mount sdcardfs filesystem";
+            return false;
+        }
     }
-
     return true;
 }
 
@@ -355,7 +369,8 @@ static bool sdcardfs_setup_bind_remount(const std::string& source_path, const st
 }
 
 static void run_sdcardfs(const std::string& source_path, const std::string& label, uid_t uid,
-        gid_t gid, userid_t userid, bool multi_user, bool full_write) {
+                         gid_t gid, userid_t userid, bool multi_user, bool full_write,
+                         bool derive_gid) {
     std::string dest_path_default = "/mnt/runtime/default/" + label;
     std::string dest_path_read = "/mnt/runtime/read/" + label;
     std::string dest_path_write = "/mnt/runtime/write/" + label;
@@ -365,10 +380,10 @@ static void run_sdcardfs(const std::string& source_path, const std::string& labe
         // Multi-user storage is fully isolated per user, so "other"
         // permissions are completely masked off.
         if (!sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,
-                                                      AID_SDCARD_RW, 0006)
-                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read, AID_EVERYBODY, 0027)
-                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write,
-                                                      AID_EVERYBODY, full_write ? 0007 : 0027)) {
+                            AID_SDCARD_RW, 0006, derive_gid) ||
+            !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read, AID_EVERYBODY, 0027) ||
+            !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write, AID_EVERYBODY,
+                                         full_write ? 0007 : 0027)) {
             LOG(FATAL) << "failed to sdcardfs_setup";
         }
     } else {
@@ -376,11 +391,11 @@ static void run_sdcardfs(const std::string& source_path, const std::string& labe
         // the Android directories are masked off to a single user
         // deep inside attr_from_stat().
         if (!sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,
-                                                      AID_SDCARD_RW, 0006)
-                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read,
-                                                      AID_EVERYBODY, full_write ? 0027 : 0022)
-                || !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write,
-                                                      AID_EVERYBODY, full_write ? 0007 : 0022)) {
+                            AID_SDCARD_RW, 0006, derive_gid) ||
+            !sdcardfs_setup_bind_remount(dest_path_default, dest_path_read, AID_EVERYBODY,
+                                         full_write ? 0027 : 0022) ||
+            !sdcardfs_setup_bind_remount(dest_path_default, dest_path_write, AID_EVERYBODY,
+                                         full_write ? 0007 : 0022)) {
             LOG(FATAL) << "failed to sdcardfs_setup";
         }
     }
@@ -437,7 +452,8 @@ static int usage() {
                << "    -g: specify GID to run as"
                << "    -U: specify user ID that owns device"
                << "    -m: source_path is multi-user"
-               << "    -w: runtime write mount has full write access";
+               << "    -w: runtime write mount has full write access"
+               << "    -P  preserve owners on the lower file system";
     return 1;
 }
 
@@ -449,12 +465,13 @@ int main(int argc, char **argv) {
     userid_t userid = 0;
     bool multi_user = false;
     bool full_write = false;
+    bool derive_gid = false;
     int i;
     struct rlimit rlim;
     int fs_version;
 
     int opt;
-    while ((opt = getopt(argc, argv, "u:g:U:mw")) != -1) {
+    while ((opt = getopt(argc, argv, "u:g:U:mwG")) != -1) {
         switch (opt) {
             case 'u':
                 uid = strtoul(optarg, NULL, 10);
@@ -471,6 +488,9 @@ int main(int argc, char **argv) {
             case 'w':
                 full_write = true;
                 break;
+            case 'G':
+                derive_gid = true;
+                break;
             case '?':
             default:
                 return usage();
@@ -514,7 +534,7 @@ int main(int argc, char **argv) {
     }
 
     if (should_use_sdcardfs()) {
-        run_sdcardfs(source_path, label, uid, gid, userid, multi_user, full_write);
+        run_sdcardfs(source_path, label, uid, gid, userid, multi_user, full_write, derive_gid);
     } else {
         run(source_path, label, uid, gid, userid, multi_user, full_write);
     }