Add app's own UID to the default ACL. am: 1129b81071 am: 55565a991f
Original change: https://googleplex-android-review.googlesource.com/c/platform/system/vold/+/11871333
Change-Id: Iaec02373329881afa98db8cae68410fccd5d3e00
diff --git a/Utils.cpp b/Utils.cpp
index e3a419f..cc6cb78 100644
--- a/Utils.cpp
+++ b/Utils.cpp
@@ -131,14 +131,15 @@
}
// Sets a default ACL on the directory.
-int SetDefaultAcl(const std::string& path, mode_t mode, uid_t uid, gid_t gid) {
+int SetDefaultAcl(const std::string& path, mode_t mode, uid_t uid, gid_t gid,
+ std::vector<gid_t> additionalGids) {
if (IsSdcardfsUsed()) {
// sdcardfs magically takes care of this
return OK;
}
- static constexpr size_t size =
- sizeof(posix_acl_xattr_header) + 3 * sizeof(posix_acl_xattr_entry);
+ size_t num_entries = 3 + (additionalGids.size() > 0 ? additionalGids.size() + 1 : 0);
+ size_t size = sizeof(posix_acl_xattr_header) + num_entries * sizeof(posix_acl_xattr_entry);
auto buf = std::make_unique<uint8_t[]>(size);
posix_acl_xattr_header* acl_header = reinterpret_cast<posix_acl_xattr_header*>(buf.get());
@@ -147,23 +148,41 @@
posix_acl_xattr_entry* entry =
reinterpret_cast<posix_acl_xattr_entry*>(buf.get() + sizeof(posix_acl_xattr_header));
- entry[0].e_tag = ACL_USER_OBJ;
+ int tag_index = 0;
+
+ entry[tag_index].e_tag = ACL_USER_OBJ;
// The existing mode_t mask has the ACL in the lower 9 bits:
// the lowest 3 for "other", the next 3 the group, the next 3 for the owner
// Use the mode_t masks to get these bits out, and shift them to get the
// correct value per entity.
//
// Eg if mode_t = 0700, rwx for the owner, then & S_IRWXU >> 6 results in 7
- entry[0].e_perm = (mode & S_IRWXU) >> 6;
- entry[0].e_id = uid;
+ entry[tag_index].e_perm = (mode & S_IRWXU) >> 6;
+ entry[tag_index].e_id = uid;
+ tag_index++;
- entry[1].e_tag = ACL_GROUP_OBJ;
- entry[1].e_perm = (mode & S_IRWXG) >> 3;
- entry[1].e_id = gid;
+ entry[tag_index].e_tag = ACL_GROUP_OBJ;
+ entry[tag_index].e_perm = (mode & S_IRWXG) >> 3;
+ entry[tag_index].e_id = gid;
+ tag_index++;
- entry[2].e_tag = ACL_OTHER;
- entry[2].e_perm = mode & S_IRWXO;
- entry[2].e_id = 0;
+ if (additionalGids.size() > 0) {
+ for (gid_t additional_gid : additionalGids) {
+ entry[tag_index].e_tag = ACL_GROUP;
+ entry[tag_index].e_perm = (mode & S_IRWXG) >> 3;
+ entry[tag_index].e_id = additional_gid;
+ tag_index++;
+ }
+
+ entry[tag_index].e_tag = ACL_MASK;
+ entry[tag_index].e_perm = (mode & S_IRWXG) >> 3;
+ entry[tag_index].e_id = 0;
+ tag_index++;
+ }
+
+ entry[tag_index].e_tag = ACL_OTHER;
+ entry[tag_index].e_perm = mode & S_IRWXO;
+ entry[tag_index].e_id = 0;
int ret = setxattr(path.c_str(), XATTR_NAME_POSIX_ACL_DEFAULT, acl_header, size, 0);
@@ -287,6 +306,7 @@
uid_t uid = appUid;
gid_t gid = AID_MEDIA_RW;
+ std::vector<gid_t> additionalGids;
std::string appDir;
// Check that the next part matches one of the allowed Android/ dirs
@@ -294,6 +314,10 @@
appDir = kAppDataDir;
if (!sdcardfsSupport) {
gid = AID_EXT_DATA_RW;
+ // Also add the app's own UID as a group; since apps belong to a group
+ // that matches their UID, this ensures that they will always have access to
+ // the files created in these dirs, even if they are created by other processes
+ additionalGids.push_back(uid);
}
} else if (StartsWith(pathFromRoot, kAppMediaDir)) {
appDir = kAppMediaDir;
@@ -304,6 +328,8 @@
appDir = kAppObbDir;
if (!sdcardfsSupport) {
gid = AID_EXT_OBB_RW;
+ // See comments for kAppDataDir above
+ additionalGids.push_back(uid);
}
} else {
LOG(ERROR) << "Invalid application directory: " << path;
@@ -364,7 +390,7 @@
// installers and MTP, that require access here.
//
// See man (5) acl for more details.
- ret = SetDefaultAcl(pathToCreate, mode, uid, gid);
+ ret = SetDefaultAcl(pathToCreate, mode, uid, gid, additionalGids);
if (ret != 0) {
return ret;
}
@@ -1522,7 +1548,7 @@
// Some other apps, like installers, have write access to the OBB directory
// to pre-download them. To make sure newly created folders in this directory
// have the right permissions, set a default ACL.
- SetDefaultAcl(androidObbDir, mode, AID_MEDIA_RW, obbGid);
+ SetDefaultAcl(androidObbDir, mode, AID_MEDIA_RW, obbGid, {});
if (fs_prepare_dir(androidMediaDir.c_str(), mode, AID_MEDIA_RW, AID_MEDIA_RW) != 0) {
PLOG(ERROR) << "Failed to create " << androidMediaDir;