From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f201.google.com ([209.85.160.201]:49592 "EHLO mail-qt1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727802AbeJEDZI (ORCPT ); Thu, 4 Oct 2018 23:25:08 -0400 Received: by mail-qt1-f201.google.com with SMTP id f20-v6so9677037qta.16 for ; Thu, 04 Oct 2018 13:30:13 -0700 (PDT) Date: Thu, 4 Oct 2018 13:30:05 -0700 In-Reply-To: <20181004203007.217320-1-mjg59@google.com> Message-Id: <20181004203007.217320-2-mjg59@google.com> Mime-Version: 1.0 References: <20181004203007.217320-1-mjg59@google.com> Subject: [PATCH 1/3] VFS: Add a call to obtain a file's hash From: Matthew Garrett To: linux-integrity@vger.kernel.org Cc: zohar@linux.vnet.ibm.com, dmitry.kasatkin@gmail.com, miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, Matthew Garrett Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: IMA wants to know what the hash of a file is, and currently does so by reading the entire file and generating the hash. Some filesystems may have the ability to store the hash in a secure manner resistant to offline attacks (eg, filesystem-level file signing), and in that case it's a performance win for IMA to be able to use that rather than having to re-hash everything. This patch simply adds VFS-level support for calling down to filesystems. Signed-off-by: Matthew Garrett --- fs/read_write.c | 24 ++++++++++++++++++++++++ include/linux/fs.h | 6 +++++- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/fs/read_write.c b/fs/read_write.c index 39b4a21dd933..9ba3ce4bb838 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -2081,3 +2081,27 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same) return ret; } EXPORT_SYMBOL(vfs_dedupe_file_range); + +/** + * vfs_gethash - obtain a file's hash + * @file: file structure in question + * @hash_algo: the hash algorithm requested + * @buf: buffer to return the hash in + * @size: size allocated for the buffer by the caller + * + * This function allows filesystems that support securely storing the hash + * of a file to return it rather than forcing the kernel to recalculate it. + * Filesystems that cannot provide guarantees about the hash being resistant + * to offline attack should not implement this functionality. + * + * Returns 0 on success, -EOPNOTSUPP if the filesystem doesn't support it. + */ +int vfs_get_hash(struct file *file, enum hash_algo hash, uint8_t *buf, + size_t size) +{ + if (!file->f_op->get_hash) + return -EOPNOTSUPP; + + return file->f_op->get_hash(file, hash, buf, size); +} +EXPORT_SYMBOL(vfs_get_hash); diff --git a/include/linux/fs.h b/include/linux/fs.h index 6c0b4a1c22ff..540316cfd461 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -40,6 +40,7 @@ #include #include +#include struct backing_dev_info; struct bdi_writeback; @@ -1764,6 +1765,8 @@ struct file_operations { int (*dedupe_file_range)(struct file *, loff_t, struct file *, loff_t, u64); int (*fadvise)(struct file *, loff_t, loff_t, int); + int (*get_hash)(struct file *, enum hash_algo hash, uint8_t *buf, + size_t size); } __randomize_layout; struct inode_operations { @@ -1838,7 +1841,8 @@ extern int vfs_dedupe_file_range(struct file *file, extern int vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos, struct file *dst_file, loff_t dst_pos, u64 len); - +extern int vfs_get_hash(struct file *file, enum hash_algo hash, uint8_t *buf, + size_t size); struct super_operations { struct inode *(*alloc_inode)(struct super_block *sb); -- 2.19.0.605.g01d371f741-goog