Commit cdb67279 authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

ovl: lookup whiteouts outside iterate_dir() 



If jffs2 can deadlock on overlayfs readdir because it takes the same lock
on ->iterate() as in ->lookup().

Fix by moving whiteout checking outside iterate_dir().  Optimized by
collecting potential whiteouts (DT_CHR) in a temporary list and if
non-empty iterating throug these and checking for a 0/0 chardev.

Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
Fixes: 49c21e1c ("ovl: check whiteout while reading directory")
Reported-by: default avatarRoman Yeryomin <leroi.lists@gmail.com>
parent 7c03b5d4

fs/overlayfs/readdir.c

+49 −28
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ struct ovl_cache_entry { 
	u64 ino;

	struct list_head l_node;

	struct rb_node node;

	struct ovl_cache_entry *next_maybe_whiteout;

	bool is_whiteout;

	char name[];

};
@@ -39,7 +40,7 @@ struct ovl_readdir_data { 
	struct rb_root root;

	struct list_head *list;

	struct list_head middle;

	struct dentry *dir;

	struct ovl_cache_entry *first_maybe_whiteout;

	int count;

	int err;

};
@@ -79,7 +80,7 @@ static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root, 
	return NULL;

}



static struct ovl_cache_entry *ovl_cache_entry_new(struct dentry *dir,

static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,

						   const char *name, int len,

						   u64 ino, unsigned int d_type)

{
@@ -98,29 +99,8 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct dentry *dir, 
	p->is_whiteout = false;



	if (d_type == DT_CHR) {

		struct dentry *dentry;

		const struct cred *old_cred;

		struct cred *override_cred;



		override_cred = prepare_creds();

		if (!override_cred) {

			kfree(p);

			return NULL;

		}



		/*

		 * CAP_DAC_OVERRIDE for lookup

		 */

		cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);

		old_cred = override_creds(override_cred);



		dentry = lookup_one_len(name, dir, len);

		if (!IS_ERR(dentry)) {

			p->is_whiteout = ovl_is_whiteout(dentry);

			dput(dentry);

		}

		revert_creds(old_cred);

		put_cred(override_cred);

		p->next_maybe_whiteout = rdd->first_maybe_whiteout;

		rdd->first_maybe_whiteout = p;

	}

	return p;

}
@@ -148,7 +128,7 @@ static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd, 
			return 0;

	}



	p = ovl_cache_entry_new(rdd->dir, name, len, ino, d_type);

	p = ovl_cache_entry_new(rdd, name, len, ino, d_type);

	if (p == NULL)

		return -ENOMEM;
@@ -169,7 +149,7 @@ static int ovl_fill_lower(struct ovl_readdir_data *rdd, 
	if (p) {

		list_move_tail(&p->l_node, &rdd->middle);

	} else {

		p = ovl_cache_entry_new(rdd->dir, name, namelen, ino, d_type);

		p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);

		if (p == NULL)

			rdd->err = -ENOMEM;

		else
@@ -219,6 +199,43 @@ static int ovl_fill_merge(struct dir_context *ctx, const char *name, 
		return ovl_fill_lower(rdd, name, namelen, offset, ino, d_type);

}



static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)

{

	int err;

	struct ovl_cache_entry *p;

	struct dentry *dentry;

	const struct cred *old_cred;

	struct cred *override_cred;



	override_cred = prepare_creds();

	if (!override_cred)

		return -ENOMEM;



	/*

	 * CAP_DAC_OVERRIDE for lookup

	 */

	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);

	old_cred = override_creds(override_cred);



	err = mutex_lock_killable(&dir->d_inode->i_mutex);

	if (!err) {

		while (rdd->first_maybe_whiteout) {

			p = rdd->first_maybe_whiteout;

			rdd->first_maybe_whiteout = p->next_maybe_whiteout;

			dentry = lookup_one_len(p->name, dir, p->len);

			if (!IS_ERR(dentry)) {

				p->is_whiteout = ovl_is_whiteout(dentry);

				dput(dentry);

			}

		}

		mutex_unlock(&dir->d_inode->i_mutex);

	}

	revert_creds(old_cred);

	put_cred(override_cred);



	return err;

}



static inline int ovl_dir_read(struct path *realpath,

			       struct ovl_readdir_data *rdd)

{
@@ -229,7 +246,7 @@ static inline int ovl_dir_read(struct path *realpath, 
	if (IS_ERR(realfile))

		return PTR_ERR(realfile);



	rdd->dir = realpath->dentry;

	rdd->first_maybe_whiteout = NULL;

	rdd->ctx.pos = 0;

	do {

		rdd->count = 0;
@@ -238,6 +255,10 @@ static inline int ovl_dir_read(struct path *realpath, 
		if (err >= 0)

			err = rdd->err;

	} while (!err && rdd->count);



	if (!err && rdd->first_maybe_whiteout)

		err = ovl_check_whiteouts(realpath->dentry, rdd);



	fput(realfile);



	return err;

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