5 files changed, 21 insertions, 4 deletions
diff --git a/fs/sdcardfs/derived_perm.c b/fs/sdcardfs/derived_perm.c
index 85a60fb5ff39..e0b74dc77c5f 100644
--- a/fs/sdcardfs/derived_perm.c
+++ b/fs/sdcardfs/derived_perm.c
@@ -176,6 +176,9 @@ void fixup_lower_ownership(struct dentry *dentry, const char *name)
 	gid_t gid = sbi->options.fs_low_gid;
 	struct iattr newattrs;
 
+	if (!sbi->options.gid_derivation)
+		return;
+
 	info = SDCARDFS_I(d_inode(dentry));
 	info_d = info->data;
 	perm = info_d->perm;
diff --git a/fs/sdcardfs/inode.c b/fs/sdcardfs/inode.c
index 103dc45a131f..85eb8ebb5372 100644
--- a/fs/sdcardfs/inode.c
+++ b/fs/sdcardfs/inode.c
@@ -34,10 +34,14 @@ const struct cred *override_fsids(struct sdcardfs_sb_info *sbi,
 	if (!cred)
 		return NULL;
 
-	if (data->under_obb)
-		uid = AID_MEDIA_OBB;
-	else
-		uid = multiuser_get_uid(data->userid, sbi->options.fs_low_uid);
+	if (sbi->options.gid_derivation) {
+		if (data->under_obb)
+			uid = AID_MEDIA_OBB;
+		else
+			uid = multiuser_get_uid(data->userid, sbi->options.fs_low_uid);
+	} else {
+		uid = sbi->options.fs_low_uid;
+	}
 	cred->fsuid = make_kuid(&init_user_ns, uid);
 	cred->fsgid = make_kgid(&init_user_ns, sbi->options.fs_low_gid);
 
diff --git a/fs/sdcardfs/main.c b/fs/sdcardfs/main.c
index 80825b287836..0a2b5167e9a2 100644
--- a/fs/sdcardfs/main.c
+++ b/fs/sdcardfs/main.c
@@ -32,6 +32,7 @@ enum {
 	Opt_multiuser,
 	Opt_userid,
 	Opt_reserved_mb,
+	Opt_gid_derivation,
 	Opt_err,
 };
 
@@ -43,6 +44,7 @@ static const match_table_t sdcardfs_tokens = {
 	{Opt_mask, "mask=%u"},
 	{Opt_userid, "userid=%d"},
 	{Opt_multiuser, "multiuser"},
+	{Opt_gid_derivation, "derive_gid"},
 	{Opt_reserved_mb, "reserved_mb=%u"},
 	{Opt_err, NULL}
 };
@@ -64,6 +66,8 @@ static int parse_options(struct super_block *sb, char *options, int silent,
 	vfsopts->gid = 0;
 	/* by default, 0MB is reserved */
 	opts->reserved_mb = 0;
+	/* by default, gid derivation is off */
+	opts->gid_derivation = false;
 
 	*debug = 0;
 
@@ -115,6 +119,9 @@ static int parse_options(struct super_block *sb, char *options, int silent,
 				return 0;
 			opts->reserved_mb = option;
 			break;
+		case Opt_gid_derivation:
+			opts->gid_derivation = true;
+			break;
 		/* unknown option */
 		default:
 			if (!silent)
diff --git a/fs/sdcardfs/sdcardfs.h b/fs/sdcardfs/sdcardfs.h
index b8624fd8b817..88b92b2f1872 100644
--- a/fs/sdcardfs/sdcardfs.h
+++ b/fs/sdcardfs/sdcardfs.h
@@ -219,6 +219,7 @@ struct sdcardfs_mount_options {
 	gid_t fs_low_gid;
 	userid_t fs_user_id;
 	bool multiuser;
+	bool gid_derivation;
 	unsigned int reserved_mb;
 };
 
diff --git a/fs/sdcardfs/super.c b/fs/sdcardfs/super.c
index 7f4539b4b249..b89947d878e3 100644
--- a/fs/sdcardfs/super.c
+++ b/fs/sdcardfs/super.c
@@ -302,6 +302,8 @@ static int sdcardfs_show_options(struct vfsmount *mnt, struct seq_file *m,
 		seq_printf(m, ",mask=%u", vfsopts->mask);
 	if (opts->fs_user_id)
 		seq_printf(m, ",userid=%u", opts->fs_user_id);
+	if (opts->gid_derivation)
+		seq_puts(m, ",derive_gid");
 	if (opts->reserved_mb != 0)
 		seq_printf(m, ",reserved=%uMB", opts->reserved_mb);