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  1. ae75f37 Include local headers first by Eric Biggers · 3 years, 5 months ago master
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This is fsverity, a userspace utility for fs-verity. fs-verity is a Linux kernel feature that does transparent on-demand integrity/authenticity verification of the contents of read-only files, using a hidden Merkle tree (hash tree) associated with the file. The mechanism is similar to dm-verity, but implemented at the file level rather than at the block device level. The fsverity utility allows you to set up fs-verity protected files.

fs-verity will initially be supported by the ext4 and f2fs filesystems, but it may later be supported by other filesystems too.

Building and installing

The fsverity utility uses the OpenSSL library, so you first must install the needed development files. For example, on Debian-based systems, run:

    sudo apt-get install libssl-dev

OpenSSL must be version 1.0.0 or later.

Then, to build and install:

    sudo make install


Basic use

    mkfs.ext4 -O verity /dev/vdc
    mount /dev/vdc /vdc
    cd /vdc

    # Create a test file
    head -c 1000000 /dev/urandom > file
    md5sum file

    # Enable verity on the file
    fsverity enable file

    # Show the verity file measurement
    fsverity measure file

    # File should still be readable as usual.  However, all data read
    # is now transparently checked against a hidden Merkle tree, whose
    # root hash is incorporated into the verity file measurement.
    # Reads of any corrupted parts of the data will fail.
    md5sum file

Note that in the above example, the file isn't signed. Therefore, to get any authenticity protection (as opposed to just integrity protection), the output of fsverity measure needs to be compared against a trusted value.

Using builtin signatures

With CONFIG_FS_VERITY_BUILTIN_SIGNATURES=y, the filesystem supports automatically verifying a signed file measurement that has been included in the verity metadata. The signature is verified against the set of X.509 certificates that have been loaded into the “.fs-verity” kernel keyring. Here's an example:

    # Generate a new certificate and private key:
    openssl req -newkey rsa:4096 -nodes -keyout key.pem -x509 -out cert.pem

    # Convert the certificate from PEM to DER format:
    openssl x509 -in cert.pem -out cert.der -outform der

    # Load the certificate into the fs-verity keyring:
    keyctl padd asymmetric '' %keyring:.fs-verity < cert.der

    # Optionally, lock the keyring so that no more keys can be added
    # (requires keyctl v1.5.11 or later):
    keyctl restrict_keyring %keyring:.fs-verity

    # Optionally, require that all verity files be signed:
    sysctl fs.verity.require_signatures=1

    # Now set up fs-verity on a test file:
    md5sum file
    fsverity sign file file.sig --key=key.pem --cert=cert.pem
    fsverity enable file --signature=file.sig
    rm -f file.sig
    md5sum file

By default, it‘s not required that verity files have a signature. This can be changed with sysctl fs.verity.require_signatures=1. When set, it’s guaranteed that the contents of every verity file has been signed by one of the certificates in the keyring.

Note: applications generally still need to check whether the file they're accessing really is a verity file, since an attacker could replace a verity file with a regular one.

With IMA

IMA support for fs-verity is planned.


This project is provided under the terms of the GNU General Public License, version 2; or at your option, any later version. A copy of the GPLv2 can be found in the file named COPYING.

Permission to link to OpenSSL (libcrypto) is granted.

Send questions and bug reports to

Submitting patches

Send patches to Patches should follow the Linux kernel's coding style. Additionally, like the Linux kernel itself, patches require the following “sign-off” procedure:

The sign-off is a simple line at the end of the explanation for the patch, which certifies that you wrote it or otherwise have the right to pass it on as an open-source patch. The rules are pretty simple: if you can certify the below:

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

    (a) The contribution was created in whole or in part by me and I
        have the right to submit it under the open source license
        indicated in the file; or

    (b) The contribution is based upon previous work that, to the best
        of my knowledge, is covered under an appropriate open source
        license and I have the right under that license to submit that
        work with modifications, whether created in whole or in part
        by me, under the same open source license (unless I am
        permitted to submit under a different license), as indicated
        in the file; or

    (c) The contribution was provided directly to me by some other
        person who certified (a), (b) or (c) and I have not modified

    (d) I understand and agree that this project and the contribution
        are public and that a record of the contribution (including all
        personal information I submit with it, including my sign-off) is
        maintained indefinitely and may be redistributed consistent with
        this project or the open source license(s) involved.

then you just add a line saying::

Signed-off-by: Random J Developer <>

using your real name (sorry, no pseudonyms or anonymous contributions.)