From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH v4 10/16] fs-verity: implement FS_IOC_ENABLE_VERITY ioctl Date: Tue, 18 Jun 2019 09:50:18 -0700 Message-ID: <20190618165017.GD184520@gmail.com> References: <20190606155205.2872-1-ebiggers@kernel.org> <20190606155205.2872-11-ebiggers@kernel.org> <20190615150821.GK6142@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20190615150821.GK6142@mit.edu> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net To: Theodore Ts'o Cc: "Darrick J . Wong" , linux-api@vger.kernel.org, Dave Chinner , linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jaegeuk Kim , linux-integrity@vger.kernel.org, linux-ext4@vger.kernel.org, Linus Torvalds , Christoph Hellwig , Victor Hsieh List-Id: linux-api@vger.kernel.org On Sat, Jun 15, 2019 at 11:08:21AM -0400, Theodore Ts'o wrote: > On Thu, Jun 06, 2019 at 08:51:59AM -0700, Eric Biggers wrote: > > From: Eric Biggers > > > > Add a function for filesystems to call to implement the > > FS_IOC_ENABLE_VERITY ioctl. This ioctl enables fs-verity on a file. > > > > See the "FS_IOC_ENABLE_VERITY" section of > > Documentation/filesystems/fsverity.rst for the documentation. > > > > Signed-off-by: Eric Biggers > > > diff --git a/fs/verity/enable.c b/fs/verity/enable.c > > new file mode 100644 > > index 000000000000..7e7ef9d3c376 > > --- /dev/null > > +++ b/fs/verity/enable.c > > + /* Tell the filesystem to finish enabling verity on the file */ > > + err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size); > > + if (err) { > > + fsverity_err(inode, "%ps() failed with err %d", > > + vops->end_enable_verity, err); > > + fsverity_free_info(vi); > > + } else { > > + /* Successfully enabled verity */ > > + > > + WARN_ON(!IS_VERITY(inode)); > > + > > + /* > > + * Readers can start using ->i_verity_info immediately, so it > > + * can't be rolled back once set. So don't set it until just > > + * after the filesystem has successfully enabled verity. > > + */ > > + fsverity_set_info(inode, vi); > > + } > > If end_enable_Verity() retuns success, and IS_VERITY is not set, I > would think that we should report the error via fsverity_err() and > return an error to userspace, and *not* call fsverity_set_info(). I > don't think the stack trace printed by WARN_ON is going to very > interesting, since the call path which gets us to enable_verity() is > not going to be surprising. > I want to keep it as WARN_ON() because if it happens it's a kernel bug, and WARNs are reported as bugs by automated tools. But I can do the following so it returns an error code too: @@ -229,11 +235,12 @@ static int enable_verity(struct file *filp, fsverity_err(inode, "%ps() failed with err %d", vops->end_enable_verity, err); fsverity_free_info(vi); + } else if (WARN_ON(!IS_VERITY(inode))) { + err = -EINVAL; + fsverity_free_info(vi); } else { /* Successfully enabled verity */ - WARN_ON(!IS_VERITY(inode)); - /* * Readers can start using ->i_verity_info immediately, so it * can't be rolled back once set. So don't set it until just > > + > > + if (inode->i_size <= 0) { > > + err = -EINVAL; > > + goto out_unlock; > > + } > > How hard would it be to support fsverity for zero-length files? There > would be no Merkle tree, but there still would be an fsverity header > file on which we can calculate a checksum for the digital signature. > > - Ted > Empty files would have to be special-cased, e.g. defining the root hash to be all 0's, since there are no blocks to checksum. It would be straightforward, but it would still be a special case, e.g.: diff --git a/fs/verity/enable.c b/fs/verity/enable.c index ee9dd578e59fb..e859a2b6a4310 100644 --- a/fs/verity/enable.c +++ b/fs/verity/enable.c @@ -112,6 +112,12 @@ static int build_merkle_tree(struct inode *inode, unsigned int level; int err = -ENOMEM; + if (inode->i_size == 0) { + /* Empty file is a special case; root hash is all 0's */ + memset(root_hash, 0, params->digest_size); + return 0; + } + On the other hand, *not* supporting empty files is a special case from the user's point of view. It means that fs-verity isn't supported on every possible file. Thinking about it, that's probably worse than having a special case in the *implementation*. So now I'm leaning towards changing it to support empty files. - Eric