Unverified Commit ff7c4ea1 authored by NeilBrown's avatar NeilBrown Committed by Christian Brauner
Browse files

VFS: add start_creating_killable() and start_removing_killable() 



These are similar to start_creating() and start_removing(), but allow a
fatal signal to abort waiting for the lock.

They are used in btrfs for subvol creation and removal.

btrfs_may_create() no longer needs IS_DEADDIR() and
start_creating_killable() includes that check.

Reviewed-by: default avatarAmir Goldstein <amir73il@gmail.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarNeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20251113002050.676694-10-neilb@ownmail.net


Tested-by: default avatar <syzbot@syzkaller.appspotmail.com>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 7bb1eb45

fs/btrfs/ioctl.c

+12 −29
Original line number Diff line number Diff line
@@ -904,14 +904,9 @@ static noinline int btrfs_mksubvol(struct dentry *parent, 
	struct fscrypt_str name_str = FSTR_INIT((char *)qname->name, qname->len);

	int ret;



	ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT);

	if (ret == -EINTR)

		return ret;



	dentry = lookup_one(idmap, qname, parent);

	ret = PTR_ERR(dentry);

	dentry = start_creating_killable(idmap, parent, qname);

	if (IS_ERR(dentry))

		goto out_unlock;

		return PTR_ERR(dentry);



	ret = btrfs_may_create(idmap, dir, dentry);

	if (ret)
@@ -940,9 +935,7 @@ static noinline int btrfs_mksubvol(struct dentry *parent, 
out_up_read:

	up_read(&fs_info->subvol_sem);

out_dput:

	dput(dentry);

out_unlock:

	btrfs_inode_unlock(BTRFS_I(dir), 0);

	end_creating(dentry, parent);

	return ret;

}
@@ -2417,18 +2410,10 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, 
		goto free_subvol_name;

	}



	ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT);

	if (ret == -EINTR)

		goto free_subvol_name;

	dentry = lookup_one(idmap, &QSTR(subvol_name), parent);

	dentry = start_removing_killable(idmap, parent, &QSTR(subvol_name));

	if (IS_ERR(dentry)) {

		ret = PTR_ERR(dentry);

		goto out_unlock_dir;

	}



	if (d_really_is_negative(dentry)) {

		ret = -ENOENT;

		goto out_dput;

		goto out_end_removing;

	}



	inode = d_inode(dentry);
@@ -2449,7 +2434,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, 
		 */

		ret = -EPERM;

		if (!btrfs_test_opt(fs_info, USER_SUBVOL_RM_ALLOWED))

			goto out_dput;

			goto out_end_removing;



		/*

		 * Do not allow deletion if the parent dir is the same
@@ -2460,21 +2445,21 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, 
		 */

		ret = -EINVAL;

		if (root == dest)

			goto out_dput;

			goto out_end_removing;



		ret = inode_permission(idmap, inode, MAY_WRITE | MAY_EXEC);

		if (ret)

			goto out_dput;

			goto out_end_removing;

	}



	/* check if subvolume may be deleted by a user */

	ret = btrfs_may_delete(idmap, dir, dentry, 1);

	if (ret)

		goto out_dput;

		goto out_end_removing;



	if (btrfs_ino(BTRFS_I(inode)) != BTRFS_FIRST_FREE_OBJECTID) {

		ret = -EINVAL;

		goto out_dput;

		goto out_end_removing;

	}



	btrfs_inode_lock(BTRFS_I(inode), 0);
@@ -2483,10 +2468,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, 
	if (!ret)

		d_delete_notify(dir, dentry);



out_dput:

	dput(dentry);

out_unlock_dir:

	btrfs_inode_unlock(BTRFS_I(dir), 0);

out_end_removing:

	end_removing(dentry);

free_subvol_name:

	kfree(subvol_name_ptr);

free_parent:

fs/namei.c

+77 −3
Original line number Diff line number Diff line
@@ -2778,19 +2778,33 @@ static int filename_parentat(int dfd, struct filename *name, 
 * Returns: a locked dentry, or an error.

 *

 */

struct dentry *start_dirop(struct dentry *parent, struct qstr *name,

			   unsigned int lookup_flags)

static struct dentry *__start_dirop(struct dentry *parent, struct qstr *name,

				    unsigned int lookup_flags,

				    unsigned int state)

{

	struct dentry *dentry;

	struct inode *dir = d_inode(parent);



	if (state == TASK_KILLABLE) {

		int ret = down_write_killable_nested(&dir->i_rwsem,

						     I_MUTEX_PARENT);

		if (ret)

			return ERR_PTR(ret);

	} else {

		inode_lock_nested(dir, I_MUTEX_PARENT);

	}

	dentry = lookup_one_qstr_excl(name, parent, lookup_flags);

	if (IS_ERR(dentry))

		inode_unlock(dir);

	return dentry;

}



struct dentry *start_dirop(struct dentry *parent, struct qstr *name,

			   unsigned int lookup_flags)

{

	return __start_dirop(parent, name, lookup_flags, TASK_NORMAL);

}



/**

 * end_dirop - signal completion of a dirop

 * @de: the dentry which was returned by start_dirop or similar.
@@ -3275,6 +3289,66 @@ struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent, 
}

EXPORT_SYMBOL(start_removing);



/**

 * start_creating_killable - prepare to create a given name with permission checking

 * @idmap:  idmap of the mount

 * @parent: directory in which to prepare to create the name

 * @name:   the name to be created

 *

 * Locks are taken and a lookup in performed prior to creating

 * an object in a directory.  Permission checking (MAY_EXEC) is performed

 * against @idmap.

 *

 * If the name already exists, a positive dentry is returned.

 *

 * If a signal is received or was already pending, the function aborts

 * with -EINTR;

 *

 * Returns: a negative or positive dentry, or an error.

 */

struct dentry *start_creating_killable(struct mnt_idmap *idmap,

				       struct dentry *parent,

				       struct qstr *name)

{

	int err = lookup_one_common(idmap, name, parent);



	if (err)

		return ERR_PTR(err);

	return __start_dirop(parent, name, LOOKUP_CREATE, TASK_KILLABLE);

}

EXPORT_SYMBOL(start_creating_killable);



/**

 * start_removing_killable - prepare to remove a given name with permission checking

 * @idmap:  idmap of the mount

 * @parent: directory in which to find the name

 * @name:   the name to be removed

 *

 * Locks are taken and a lookup in performed prior to removing

 * an object from a directory.  Permission checking (MAY_EXEC) is performed

 * against @idmap.

 *

 * If the name doesn't exist, an error is returned.

 *

 * end_removing() should be called when removal is complete, or aborted.

 *

 * If a signal is received or was already pending, the function aborts

 * with -EINTR;

 *

 * Returns: a positive dentry, or an error.

 */

struct dentry *start_removing_killable(struct mnt_idmap *idmap,

				       struct dentry *parent,

				       struct qstr *name)

{

	int err = lookup_one_common(idmap, name, parent);



	if (err)

		return ERR_PTR(err);

	return __start_dirop(parent, name, 0, TASK_KILLABLE);

}

EXPORT_SYMBOL(start_removing_killable);



/**

 * start_creating_noperm - prepare to create a given name without permission checking

 * @parent: directory in which to prepare to create the name

include/linux/namei.h

+6 −0
Original line number Diff line number Diff line
@@ -92,6 +92,12 @@ struct dentry *start_creating(struct mnt_idmap *idmap, struct dentry *parent, 
			      struct qstr *name);

struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,

			      struct qstr *name);

struct dentry *start_creating_killable(struct mnt_idmap *idmap,

				       struct dentry *parent,

				       struct qstr *name);

struct dentry *start_removing_killable(struct mnt_idmap *idmap,

				       struct dentry *parent,

				       struct qstr *name);

struct dentry *start_creating_noperm(struct dentry *parent, struct qstr *name);

struct dentry *start_removing_noperm(struct dentry *parent, struct qstr *name);

struct dentry *start_removing_dentry(struct dentry *parent,