RE: [PATCH 3/5] cifsd: add file operations

[Namjae Jeon]

> On Mon, Mar 22, 2021 at 02:13:42PM +0900, Namjae Jeon wrote:
> > This adds file operations and buffer pool for cifsd.
> 
> Some random notes:
> 
> > +static void rollback_path_modification(char *filename) {
> > +	if (filename) {
> > +		filename--;
> > +		*filename = '/';
> What an odd way to spell filename[-1] = '/';...
Okay. Will fix.
> 
> > +int ksmbd_vfs_inode_permission(struct dentry *dentry, int acc_mode,
> > +bool delete) {
> 
> > +	if (delete) {
> > +		struct dentry *parent;
> > +
> > +		parent = dget_parent(dentry);
> > +		if (!parent)
> > +			return -EINVAL;
> > +
> > +		if (inode_permission(&init_user_ns, d_inode(parent), MAY_EXEC | MAY_WRITE)) {
> > +			dput(parent);
> > +			return -EACCES;
> > +		}
> > +		dput(parent);
> 
> Who's to guarantee that parent is stable?  IOW, by the time of that
> inode_permission() call dentry might very well not be a child of that thing...
Okay, Will fix.
> 
> > +	parent = dget_parent(dentry);
> > +	if (!parent)
> > +		return 0;
> > +
> > +	if (!inode_permission(&init_user_ns, d_inode(parent), MAY_EXEC | MAY_WRITE))
> > +		*daccess |= FILE_DELETE_LE;
> 
> Ditto.
Okay.
> 
> > +int ksmbd_vfs_mkdir(struct ksmbd_work *work,
> > +		    const char *name,
> > +		    umode_t mode)
> 
> 
> > +	err = vfs_mkdir(&init_user_ns, d_inode(path.dentry), dentry, mode);
> > +	if (!err) {
> > +		ksmbd_vfs_inherit_owner(work, d_inode(path.dentry),
> > +			d_inode(dentry));
> 
> ->mkdir() might very well return success, with dentry left unhashed negative.
> Look at the callers of vfs_mkdir() to see how it should be handled.
Okay, Will fix.
> 
> > +static int check_lock_range(struct file *filp,
> > +			    loff_t start,
> > +			    loff_t end,
> > +			    unsigned char type)
> > +{
> > +	struct file_lock *flock;
> > +	struct file_lock_context *ctx = file_inode(filp)->i_flctx;
> > +	int error = 0;
> > +
> > +	if (!ctx || list_empty_careful(&ctx->flc_posix))
> > +		return 0;
> > +
> > +	spin_lock(&ctx->flc_lock);
> > +	list_for_each_entry(flock, &ctx->flc_posix, fl_list) {
> > +		/* check conflict locks */
> > +		if (flock->fl_end >= start && end >= flock->fl_start) {
> > +			if (flock->fl_type == F_RDLCK) {
> > +				if (type == WRITE) {
> > +					ksmbd_err("not allow write by shared lock\n");
> > +					error = 1;
> > +					goto out;
> > +				}
> > +			} else if (flock->fl_type == F_WRLCK) {
> > +				/* check owner in lock */
> > +				if (flock->fl_file != filp) {
> > +					error = 1;
> > +					ksmbd_err("not allow rw access by exclusive lock from other
> opens\n");
> > +					goto out;
> > +				}
> > +			}
> > +		}
> > +	}
> > +out:
> > +	spin_unlock(&ctx->flc_lock);
> > +	return error;
> > +}
> 
> WTF is that doing in smbd?
This code was added to pass the smb2 lock test of samba's smbtorture.
Will fix it.
> 
> > +	filp = fp->filp;
> > +	inode = d_inode(filp->f_path.dentry);
> 
> That should be file_inode().  Try it on overlayfs, watch it do interesting things...
Okay.
> 
> > +	nbytes = kernel_read(filp, rbuf, count, pos);
> > +	if (nbytes < 0) {
> > +		name = d_path(&filp->f_path, namebuf, sizeof(namebuf));
> > +		if (IS_ERR(name))
> > +			name = "(error)";
> > +		ksmbd_err("smb read failed for (%s), err = %zd\n",
> > +				name, nbytes);
> 
> Do you really want the full pathname here?  For (presumably) spew into syslog?
No, Will fix.
> 
> > +int ksmbd_vfs_remove_file(struct ksmbd_work *work, char *name) {
> > +	struct path parent;
> > +	struct dentry *dir, *dentry;
> > +	char *last;
> > +	int err = -ENOENT;
> > +
> > +	last = extract_last_component(name);
> > +	if (!last)
> > +		return -ENOENT;
> 
> Yeccchhh...
I guess I change it err instead of -ENOENT.

> 
> > +	if (ksmbd_override_fsids(work))
> > +		return -ENOMEM;
> > +
> > +	err = kern_path(name, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &parent);
> > +	if (err) {
> > +		ksmbd_debug(VFS, "can't get %s, err %d\n", name, err);
> > +		ksmbd_revert_fsids(work);
> > +		rollback_path_modification(last);
> > +		return err;
> > +	}
> > +
> > +	dir = parent.dentry;
> > +	if (!d_inode(dir))
> > +		goto out;
> 
> Really?  When does that happen?
Will fix.
> 
> > +static int __ksmbd_vfs_rename(struct ksmbd_work *work,
> > +			      struct dentry *src_dent_parent,
> > +			      struct dentry *src_dent,
> > +			      struct dentry *dst_dent_parent,
> > +			      struct dentry *trap_dent,
> > +			      char *dst_name)
> > +{
> > +	struct dentry *dst_dent;
> > +	int err;
> > +
> > +	spin_lock(&src_dent->d_lock);
> > +	list_for_each_entry(dst_dent, &src_dent->d_subdirs, d_child) {
> > +		struct ksmbd_file *child_fp;
> > +
> > +		if (d_really_is_negative(dst_dent))
> > +			continue;
> > +
> > +		child_fp = ksmbd_lookup_fd_inode(d_inode(dst_dent));
> > +		if (child_fp) {
> > +			spin_unlock(&src_dent->d_lock);
> > +			ksmbd_debug(VFS, "Forbid rename, sub file/dir is in use\n");
> > +			return -EACCES;
> > +		}
> > +	}
> > +	spin_unlock(&src_dent->d_lock);
> 
> Hard NAK right there.  That thing has no business poking at that level.
> And I'm pretty certain that it's racy as hell.
Okay. It was same reason(smbtorture test), will fix it also.

Thanks for your review!