Commit a105d685 authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

ovl: fix remove/copy-up race 



ovl_remove_and_whiteout() needs to check if upper dentry exists or not
after having locked upper parent directory.

Previously we used a "type" value computed before locking the upper parent
directory, which is susceptible to racing with copy-up.

There's a similar check in ovl_check_empty_and_clear().  This one is not
actually racy, since copy-up doesn't change the "emptyness" property of a
directory.  Add a comment to this effect, and check the existence of upper
dentry locally to make the code cleaner.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
parent ef94b186

fs/overlayfs/dir.c

+19 −12
Original line number Diff line number Diff line
@@ -284,8 +284,7 @@ out: 
	return ERR_PTR(err);

}



static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,

						enum ovl_path_type type)

static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry)

{

	int err;

	struct dentry *ret = NULL;
@@ -294,8 +293,17 @@ static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry, 
	err = ovl_check_empty_dir(dentry, &list);

	if (err)

		ret = ERR_PTR(err);

	else if (type == OVL_PATH_MERGE)

	else {

		/*

		 * If no upperdentry then skip clearing whiteouts.

		 *

		 * Can race with copy-up, since we don't hold the upperdir

		 * mutex.  Doesn't matter, since copy-up can't create a

		 * non-empty directory from an empty one.

		 */

		if (ovl_dentry_upper(dentry))

			ret = ovl_clear_empty(dentry, &list);

	}



	ovl_cache_free(&list);
@@ -487,8 +495,7 @@ out: 
	return err;

}



static int ovl_remove_and_whiteout(struct dentry *dentry,

				   enum ovl_path_type type, bool is_dir)

static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)

{

	struct dentry *workdir = ovl_workdir(dentry);

	struct inode *wdir = workdir->d_inode;
@@ -500,7 +507,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, 
	int err;



	if (is_dir) {

		opaquedir = ovl_check_empty_and_clear(dentry, type);

		opaquedir = ovl_check_empty_and_clear(dentry);

		err = PTR_ERR(opaquedir);

		if (IS_ERR(opaquedir))

			goto out;
@@ -515,7 +522,8 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, 
	if (IS_ERR(whiteout))

		goto out_unlock;



	if (type == OVL_PATH_LOWER) {

	upper = ovl_dentry_upper(dentry);

	if (!upper) {

		upper = lookup_one_len(dentry->d_name.name, upperdir,

				       dentry->d_name.len);

		err = PTR_ERR(upper);
@@ -529,7 +537,6 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, 
	} else {

		int flags = 0;



		upper = ovl_dentry_upper(dentry);

		if (opaquedir)

			upper = opaquedir;

		err = -ESTALE;
@@ -648,7 +655,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir) 
		cap_raise(override_cred->cap_effective, CAP_CHOWN);

		old_cred = override_creds(override_cred);



		err = ovl_remove_and_whiteout(dentry, type, is_dir);

		err = ovl_remove_and_whiteout(dentry, is_dir);



		revert_creds(old_cred);

		put_cred(override_cred);
@@ -781,7 +788,7 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old, 
	}



	if (overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir) {

		opaquedir = ovl_check_empty_and_clear(new, new_type);

		opaquedir = ovl_check_empty_and_clear(new);

		err = PTR_ERR(opaquedir);

		if (IS_ERR(opaquedir)) {

			opaquedir = NULL;

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