5 files changed, 47 insertions, 10 deletions

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 3972ac87a8cb..3189a32d8fa3 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -357,7 +357,7 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	}
 out_unlock:
 	unlock_rename(workdir, upperdir);
-	revert_creds(old_cred);
+	ovl_revert_creds(old_cred);
 
 	if (link)
 		free_page((unsigned long) link);
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index eedacae889b9..953c88dd6519 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -407,7 +407,7 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
 	if (!ovl_dentry_is_opaque(dentry)) {
 		err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
 	} else {
-		const struct cred *old_cred;
+		const struct cred *old_cred, *hold_cred = NULL;
 		struct cred *override_cred;
 
 		old_cred = ovl_override_creds(dentry->d_sb);
@@ -415,15 +415,22 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
 		err = -ENOMEM;
 		override_cred = prepare_creds();
 		if (override_cred) {
-			override_cred->fsuid = old_cred->fsuid;
-			override_cred->fsgid = old_cred->fsgid;
-			put_cred(override_creds(override_cred));
+			const struct cred *our_cred;
+
+			our_cred = old_cred;
+			if (!our_cred)
+				our_cred = current_cred();
+			override_cred->fsuid = our_cred->fsuid;
+			override_cred->fsgid = our_cred->fsgid;
+			hold_cred = override_creds(override_cred);
 			put_cred(override_cred);
 
 			err = ovl_create_over_whiteout(dentry, inode, &stat,
 						       link, hardlink);
 		}
-		revert_creds(old_cred);
+		ovl_revert_creds(old_cred ?: hold_cred);
+		if (old_cred && hold_cred)
+			put_cred(hold_cred);
 	}
 
 	if (!err)
@@ -657,7 +664,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
 
 		err = ovl_remove_and_whiteout(dentry, is_dir);
 
-		revert_creds(old_cred);
+		ovl_revert_creds(old_cred);
 	}
 out_drop_write:
 	ovl_drop_write(dentry);
@@ -896,8 +903,7 @@ out_dput_old:
 out_unlock:
 	unlock_rename(new_upperdir, old_upperdir);
 out_revert_creds:
-	if (old_opaque || new_opaque)
-		revert_creds(old_cred);
+	ovl_revert_creds(old_cred);
 out_drop_write:
 	ovl_drop_write(old);
 out:
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 27a42975d7cd..0723b8f97651 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -151,6 +151,7 @@ bool ovl_dentry_is_opaque(struct dentry *dentry);
 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
 bool ovl_is_whiteout(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
+void ovl_revert_creds(const struct cred *oldcred);
 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index da999e73c97a..9ff8f8192bf1 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -223,7 +223,7 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
 		}
 		mutex_unlock(&dir->d_inode->i_mutex);
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(old_cred);
 
 	return err;
 }
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index fa20c95bd456..48f7c1ab94cd 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -31,6 +31,7 @@ struct ovl_config {
 	char *lowerdir;
 	char *upperdir;
 	char *workdir;
+	bool override_creds;
 };
 
 /* private information held for overlayfs's superblock */
@@ -252,9 +253,17 @@ const struct cred *ovl_override_creds(struct super_block *sb)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
 
+	if (!ofs->config.override_creds)
+		return NULL;
 	return override_creds(ofs->creator_cred);
 }
 
+void ovl_revert_creds(const struct cred *old_cred)
+{
+	if (old_cred)
+		revert_creds(old_cred);
+}
+
 static bool ovl_is_opaquedir(struct dentry *dentry)
 {
 	int res;
@@ -626,6 +635,11 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 	return err;
 }
 
+static bool __read_mostly ovl_override_creds_def = true;
+module_param_named(override_creds, ovl_override_creds_def, bool, 0644);
+MODULE_PARM_DESC(ovl_override_creds_def,
+		 "Use mounter's credentials for accesses");
+
 /**
  * ovl_show_options
  *
@@ -642,6 +656,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 		seq_show_option(m, "upperdir", ufs->config.upperdir);
 		seq_show_option(m, "workdir", ufs->config.workdir);
 	}
+	if (ufs->config.override_creds != ovl_override_creds_def)
+		seq_show_option(m, "override_creds",
+				ufs->config.override_creds ? "on" : "off");
 	return 0;
 }
 
@@ -666,6 +683,8 @@ enum {
 	OPT_LOWERDIR,
 	OPT_UPPERDIR,
 	OPT_WORKDIR,
+	OPT_OVERRIDE_CREDS_ON,
+	OPT_OVERRIDE_CREDS_OFF,
 	OPT_ERR,
 };
 
@@ -673,6 +692,8 @@ static const match_table_t ovl_tokens = {
 	{OPT_LOWERDIR,			"lowerdir=%s"},
 	{OPT_UPPERDIR,			"upperdir=%s"},
 	{OPT_WORKDIR,			"workdir=%s"},
+	{OPT_OVERRIDE_CREDS_ON,		"override_creds=on"},
+	{OPT_OVERRIDE_CREDS_OFF,	"override_creds=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -703,6 +724,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 {
 	char *p;
 
+	config->override_creds = ovl_override_creds_def;
 	while ((p = ovl_next_opt(&opt)) != NULL) {
 		int token;
 		substring_t args[MAX_OPT_ARGS];
@@ -733,6 +755,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 				return -ENOMEM;
 			break;
 
+		case OPT_OVERRIDE_CREDS_ON:
+			config->override_creds = true;
+			break;
+
+		case OPT_OVERRIDE_CREDS_OFF:
+			config->override_creds = false;
+			break;
+
 		default:
 			pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
 			return -EINVAL;