Re: [RFC PATCH v3 16/16] ceph: create symlinks with encrypted and base64-encoded targets

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Sep 14, 2020 at 03:17:07PM -0400, Jeff Layton wrote:
> +	if (IS_ENCRYPTED(req->r_new_inode)) {
> +		int len = strlen(dest);
> +
> +		err = fscrypt_prepare_symlink(dir, dest, len, PATH_MAX, &osd_link);
> +		if (err)
> +			goto out_req;
> +
> +		err = fscrypt_encrypt_symlink(req->r_new_inode, dest, len, &osd_link);
> +		if (err)
> +			goto out_req;
> +
> +		req->r_path2 = kmalloc(FSCRYPT_BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);

osd_link.len includes a null terminator.  It seems that's not what's wanted
here, and you should be subtracting 1 here.

(fscrypt_prepare_symlink() maybe should exclude the null terminator from the
length instead.  But for the other filesystems it was easier to include it...)

> @@ -996,26 +995,39 @@ int ceph_fill_inode(struct inode *inode, struct page *locked_page,
>  		inode->i_fop = &ceph_file_fops;
>  		break;
>  	case S_IFLNK:
> -		inode->i_op = &ceph_symlink_iops;
>  		if (!ci->i_symlink) {
>  			u32 symlen = iinfo->symlink_len;
>  			char *sym;
>  
>  			spin_unlock(&ci->i_ceph_lock);
>  
> -			if (symlen != i_size_read(inode)) {
> -				pr_err("%s %llx.%llx BAD symlink "
> -					"size %lld\n", __func__,
> -					ceph_vinop(inode),
> -					i_size_read(inode));
> +			if (IS_ENCRYPTED(inode)) {
> +				/* Do base64 decode so that we get the right size (maybe?) */
> +				err = -ENOMEM;
> +				sym = kmalloc(symlen + 1, GFP_NOFS);
> +				if (!sym)
> +					goto out;
> +
> +				symlen = fscrypt_base64_decode(iinfo->symlink, symlen, sym);
> +				/*
> +				 * i_size as reported by the MDS may be wrong, due to base64
> +				 * inflation and padding. Fix it up here.
> +				 */
>  				i_size_write(inode, symlen);

Note that fscrypt_base64_decode() can fail (return -1) if the input is not valid
base64.  That isn't being handled here.

> +static const char *ceph_encrypted_get_link(struct dentry *dentry, struct inode *inode,
> +					   struct delayed_call *done)
> +{
> +	struct ceph_inode_info *ci = ceph_inode(inode);
> +
> +	if (!dentry)
> +		return ERR_PTR(-ECHILD);
> +
> +	return fscrypt_get_symlink(inode, ci->i_symlink, ksize(ci->i_symlink), done);

Using ksize() seems wrong here, since that would allow fscrypt_get_symlink() to
read beyond the part of the buffer that is actually initialized.

> -static const struct inode_operations ceph_symlink_iops = {
> +const struct inode_operations ceph_symlink_iops = {
>  	.get_link = simple_get_link,
>  	.setattr = ceph_setattr,
>  	.getattr = ceph_getattr,
>  	.listxattr = ceph_listxattr,
>  };
>  
> +const struct inode_operations ceph_encrypted_symlink_iops = {
> +	.get_link = ceph_encrypted_get_link,
> +	.setattr = ceph_setattr,
> +	.getattr = ceph_getattr,
> +	.listxattr = ceph_listxattr,
> +};

These don't need to be made global, as they're only used in fs/ceph/inode.c.

- Eric