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fsverity updates for 5.11
Some cleanups for fs-verity: - Rename some names that have been causing confusion. - Move structs needed for file signing to the UAPI header. -----BEGIN PGP SIGNATURE----- iIoEABYIADIWIQSacvsUNc7UX4ntmEPzXCl4vpKOKwUCX9bedBQcZWJpZ2dlcnNA Z29vZ2xlLmNvbQAKCRDzXCl4vpKOK7s6AQD4xMyyPTAQbznYlxPzn+2d8H3y+qik xbX7JwATnyOM4AEApDMGPvokvmEJO4z/ionUunR20i//JIyOklxy8w4whQ0= =XO4L -----END PGP SIGNATURE----- Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt Pull fsverity updates from Eric Biggers: "Some cleanups for fs-verity: - Rename some names that have been causing confusion - Move structs needed for file signing to the UAPI header" * tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt: fs-verity: move structs needed for file signing to UAPI header fs-verity: rename "file measurement" to "file digest" fs-verity: rename fsverity_signed_digest to fsverity_formatted_digest fs-verity: remove filenames from file comments
This commit is contained in:
Linus Torvalds
commit
51895d58c7
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@ -27,9 +27,9 @@ automatically verified against the file's Merkle tree. Reads of any
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corrupted data, including mmap reads, will fail.
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Userspace can use another ioctl to retrieve the root hash (actually
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the "file measurement", which is a hash that includes the root hash)
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that fs-verity is enforcing for the file. This ioctl executes in
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constant time, regardless of the file size.
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the "fs-verity file digest", which is a hash that includes the Merkle
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tree root hash) that fs-verity is enforcing for the file. This ioctl
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executes in constant time, regardless of the file size.
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fs-verity is essentially a way to hash a file in constant time,
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subject to the caveat that reads which would violate the hash will
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@ -177,9 +177,10 @@ FS_IOC_ENABLE_VERITY can fail with the following errors:
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FS_IOC_MEASURE_VERITY
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---------------------
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The FS_IOC_MEASURE_VERITY ioctl retrieves the measurement of a verity
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file. The file measurement is a digest that cryptographically
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identifies the file contents that are being enforced on reads.
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The FS_IOC_MEASURE_VERITY ioctl retrieves the digest of a verity file.
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The fs-verity file digest is a cryptographic digest that identifies
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the file contents that are being enforced on reads; it is computed via
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a Merkle tree and is different from a traditional full-file digest.
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This ioctl takes in a pointer to a variable-length structure::
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@ -197,7 +198,7 @@ On success, 0 is returned and the kernel fills in the structure as
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follows:
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- ``digest_algorithm`` will be the hash algorithm used for the file
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measurement. It will match ``fsverity_enable_arg::hash_algorithm``.
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digest. It will match ``fsverity_enable_arg::hash_algorithm``.
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- ``digest_size`` will be the size of the digest in bytes, e.g. 32
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for SHA-256. (This can be redundant with ``digest_algorithm``.)
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- ``digest`` will be the actual bytes of the digest.
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@ -257,25 +258,24 @@ non-verity one, with the following exceptions:
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with EIO (for read()) or SIGBUS (for mmap() reads).
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- If the sysctl "fs.verity.require_signatures" is set to 1 and the
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file's verity measurement is not signed by a key in the fs-verity
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keyring, then opening the file will fail. See `Built-in signature
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verification`_.
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file is not signed by a key in the fs-verity keyring, then opening
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the file will fail. See `Built-in signature verification`_.
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Direct access to the Merkle tree is not supported. Therefore, if a
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verity file is copied, or is backed up and restored, then it will lose
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its "verity"-ness. fs-verity is primarily meant for files like
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executables that are managed by a package manager.
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File measurement computation
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============================
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File digest computation
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=======================
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This section describes how fs-verity hashes the file contents using a
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Merkle tree to produce the "file measurement" which cryptographically
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identifies the file contents. This algorithm is the same for all
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filesystems that support fs-verity.
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Merkle tree to produce the digest which cryptographically identifies
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the file contents. This algorithm is the same for all filesystems
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that support fs-verity.
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Userspace only needs to be aware of this algorithm if it needs to
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compute the file measurement itself, e.g. in order to sign the file.
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compute fs-verity file digests itself, e.g. in order to sign files.
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.. _fsverity_merkle_tree:
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@ -325,26 +325,22 @@ can't a distinguish a large file from a small second file whose data
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is exactly the top-level hash block of the first file. Ambiguities
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also arise from the convention of padding to the next block boundary.
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To solve this problem, the verity file measurement is actually
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computed as a hash of the following structure, which contains the
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Merkle tree root hash as well as other fields such as the file size::
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To solve this problem, the fs-verity file digest is actually computed
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as a hash of the following structure, which contains the Merkle tree
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root hash as well as other fields such as the file size::
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struct fsverity_descriptor {
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__u8 version; /* must be 1 */
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__u8 hash_algorithm; /* Merkle tree hash algorithm */
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__u8 log_blocksize; /* log2 of size of data and tree blocks */
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__u8 salt_size; /* size of salt in bytes; 0 if none */
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__le32 sig_size; /* must be 0 */
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__le32 __reserved_0x04; /* must be 0 */
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__le64 data_size; /* size of file the Merkle tree is built over */
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__u8 root_hash[64]; /* Merkle tree root hash */
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__u8 salt[32]; /* salt prepended to each hashed block */
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__u8 __reserved[144]; /* must be 0's */
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};
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Note that the ``sig_size`` field must be set to 0 for the purpose of
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computing the file measurement, even if a signature was provided (or
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will be provided) to `FS_IOC_ENABLE_VERITY`_.
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Built-in signature verification
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===============================
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@ -359,20 +355,20 @@ kernel. Specifically, it adds support for:
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certificates from being added.
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2. `FS_IOC_ENABLE_VERITY`_ accepts a pointer to a PKCS#7 formatted
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detached signature in DER format of the file measurement. On
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success, this signature is persisted alongside the Merkle tree.
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detached signature in DER format of the file's fs-verity digest.
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On success, this signature is persisted alongside the Merkle tree.
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Then, any time the file is opened, the kernel will verify the
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file's actual measurement against this signature, using the
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certificates in the ".fs-verity" keyring.
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file's actual digest against this signature, using the certificates
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in the ".fs-verity" keyring.
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3. A new sysctl "fs.verity.require_signatures" is made available.
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When set to 1, the kernel requires that all verity files have a
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correctly signed file measurement as described in (2).
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correctly signed digest as described in (2).
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File measurements must be signed in the following format, which is
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similar to the structure used by `FS_IOC_MEASURE_VERITY`_::
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fs-verity file digests must be signed in the following format, which
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is similar to the structure used by `FS_IOC_MEASURE_VERITY`_::
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struct fsverity_signed_digest {
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struct fsverity_formatted_digest {
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char magic[8]; /* must be "FSVerity" */
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__le16 digest_algorithm;
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__le16 digest_size;
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@ -421,8 +417,8 @@ can only be set by `FS_IOC_ENABLE_VERITY`_, and it cannot be cleared.
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ext4 also supports encryption, which can be used simultaneously with
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fs-verity. In this case, the plaintext data is verified rather than
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the ciphertext. This is necessary in order to make the file
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measurement meaningful, since every file is encrypted differently.
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the ciphertext. This is necessary in order to make the fs-verity file
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digest meaningful, since every file is encrypted differently.
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ext4 stores the verity metadata (Merkle tree and fsverity_descriptor)
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past the end of the file, starting at the first 64K boundary beyond
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@ -592,8 +588,8 @@ weren't already directly answered in other parts of this document.
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:Q: Isn't fs-verity useless because the attacker can just modify the
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hashes in the Merkle tree, which is stored on-disk?
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:A: To verify the authenticity of an fs-verity file you must verify
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the authenticity of the "file measurement", which is basically the
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root hash of the Merkle tree. See `Use cases`_.
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the authenticity of the "fs-verity file digest", which
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incorporates the root hash of the Merkle tree. See `Use cases`_.
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:Q: Isn't fs-verity useless because the attacker can just replace a
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verity file with a non-verity one?
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@ -1,6 +1,6 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/enable.c: ioctl to enable verity on a file
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* Ioctl to enable verity on a file
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*
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* Copyright 2019 Google LLC
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*/
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@ -398,9 +398,9 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
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* Some pages of the file may have been evicted from pagecache after
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* being used in the Merkle tree construction, then read into pagecache
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* again by another process reading from the file concurrently. Since
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* these pages didn't undergo verification against the file measurement
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* which fs-verity now claims to be enforcing, we have to wipe the
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* pagecache to ensure that all future reads are verified.
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* these pages didn't undergo verification against the file digest which
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* fs-verity now claims to be enforcing, we have to wipe the pagecache
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* to ensure that all future reads are verified.
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*/
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filemap_write_and_wait(inode->i_mapping);
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invalidate_inode_pages2(inode->i_mapping);
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@ -67,52 +67,22 @@ struct merkle_tree_params {
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* When a verity file is first opened, an instance of this struct is allocated
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* and stored in ->i_verity_info; it remains until the inode is evicted. It
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* caches information about the Merkle tree that's needed to efficiently verify
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* data read from the file. It also caches the file measurement. The Merkle
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* tree pages themselves are not cached here, but the filesystem may cache them.
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* data read from the file. It also caches the file digest. The Merkle tree
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* pages themselves are not cached here, but the filesystem may cache them.
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*/
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struct fsverity_info {
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struct merkle_tree_params tree_params;
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u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
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u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
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u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE];
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const struct inode *inode;
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};
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/*
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* Merkle tree properties. The file measurement is the hash of this structure
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* excluding the signature and with the sig_size field set to 0.
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*/
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struct fsverity_descriptor {
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__u8 version; /* must be 1 */
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__u8 hash_algorithm; /* Merkle tree hash algorithm */
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__u8 log_blocksize; /* log2 of size of data and tree blocks */
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__u8 salt_size; /* size of salt in bytes; 0 if none */
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__le32 sig_size; /* size of signature in bytes; 0 if none */
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__le64 data_size; /* size of file the Merkle tree is built over */
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__u8 root_hash[64]; /* Merkle tree root hash */
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__u8 salt[32]; /* salt prepended to each hashed block */
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__u8 __reserved[144]; /* must be 0's */
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__u8 signature[]; /* optional PKCS#7 signature */
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};
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/* Arbitrary limit to bound the kmalloc() size. Can be changed. */
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#define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
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#define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \
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sizeof(struct fsverity_descriptor))
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/*
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* Format in which verity file measurements are signed. This is the same as
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* 'struct fsverity_digest', except here some magic bytes are prepended to
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* provide some context about what is being signed in case the same key is used
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* for non-fsverity purposes, and here the fields have fixed endianness.
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*/
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struct fsverity_signed_digest {
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char magic[8]; /* must be "FSVerity" */
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__le16 digest_algorithm;
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__le16 digest_size;
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__u8 digest[];
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};
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/* hash_algs.c */
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extern struct fsverity_hash_alg fsverity_hash_algs[];
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@ -1,6 +1,6 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/hash_algs.c: fs-verity hash algorithms
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* fs-verity hash algorithms
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*
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* Copyright 2019 Google LLC
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*/
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|
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@ -1,6 +1,6 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/init.c: fs-verity module initialization and logging
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* fs-verity module initialization and logging
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*
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* Copyright 2019 Google LLC
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*/
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|
|
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@ -1,6 +1,6 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/measure.c: ioctl to get a verity file's measurement
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* Ioctl to get a verity file's digest
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*
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* Copyright 2019 Google LLC
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*/
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@ -10,12 +10,12 @@
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#include <linux/uaccess.h>
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/**
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* fsverity_ioctl_measure() - get a verity file's measurement
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* @filp: file to get measurement of
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* fsverity_ioctl_measure() - get a verity file's digest
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* @filp: file to get digest of
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* @_uarg: user pointer to fsverity_digest
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*
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* Retrieve the file measurement that the kernel is enforcing for reads from a
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* verity file. See the "FS_IOC_MEASURE_VERITY" section of
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* Retrieve the file digest that the kernel is enforcing for reads from a verity
|
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* file. See the "FS_IOC_MEASURE_VERITY" section of
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* Documentation/filesystems/fsverity.rst for the documentation.
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*
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* Return: 0 on success, -errno on failure
|
||||
|
|
@ -51,7 +51,7 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
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if (copy_to_user(uarg, &arg, sizeof(arg)))
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return -EFAULT;
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|
||||
if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
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if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
|
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return -EFAULT;
|
||||
|
||||
return 0;
|
||||
|
|
|
|||
|
|
@ -1,6 +1,6 @@
|
|||
// SPDX-License-Identifier: GPL-2.0
|
||||
/*
|
||||
* fs/verity/open.c: opening fs-verity files
|
||||
* Opening fs-verity files
|
||||
*
|
||||
* Copyright 2019 Google LLC
|
||||
*/
|
||||
|
|
@ -124,18 +124,18 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
|
|||
}
|
||||
|
||||
/*
|
||||
* Compute the file measurement by hashing the fsverity_descriptor excluding the
|
||||
* Compute the file digest by hashing the fsverity_descriptor excluding the
|
||||
* signature and with the sig_size field set to 0.
|
||||
*/
|
||||
static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,
|
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struct fsverity_descriptor *desc,
|
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u8 *measurement)
|
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static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
|
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struct fsverity_descriptor *desc,
|
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u8 *file_digest)
|
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{
|
||||
__le32 sig_size = desc->sig_size;
|
||||
int err;
|
||||
|
||||
desc->sig_size = 0;
|
||||
err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
|
||||
err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
|
||||
desc->sig_size = sig_size;
|
||||
|
||||
return err;
|
||||
|
|
@ -199,15 +199,15 @@ struct fsverity_info *fsverity_create_info(const struct inode *inode,
|
|||
|
||||
memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
|
||||
|
||||
err = compute_file_measurement(vi->tree_params.hash_alg, desc,
|
||||
vi->measurement);
|
||||
err = compute_file_digest(vi->tree_params.hash_alg, desc,
|
||||
vi->file_digest);
|
||||
if (err) {
|
||||
fsverity_err(inode, "Error %d computing file measurement", err);
|
||||
fsverity_err(inode, "Error %d computing file digest", err);
|
||||
goto out;
|
||||
}
|
||||
pr_debug("Computed file measurement: %s:%*phN\n",
|
||||
pr_debug("Computed file digest: %s:%*phN\n",
|
||||
vi->tree_params.hash_alg->name,
|
||||
vi->tree_params.digest_size, vi->measurement);
|
||||
vi->tree_params.digest_size, vi->file_digest);
|
||||
|
||||
err = fsverity_verify_signature(vi, desc, desc_size);
|
||||
out:
|
||||
|
|
@ -354,7 +354,7 @@ int __init fsverity_init_info_cache(void)
|
|||
{
|
||||
fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
|
||||
SLAB_RECLAIM_ACCOUNT,
|
||||
measurement);
|
||||
file_digest);
|
||||
if (!fsverity_info_cachep)
|
||||
return -ENOMEM;
|
||||
return 0;
|
||||
|
|
|
|||
|
|
@ -1,6 +1,6 @@
|
|||
// SPDX-License-Identifier: GPL-2.0
|
||||
/*
|
||||
* fs/verity/signature.c: verification of builtin signatures
|
||||
* Verification of builtin signatures
|
||||
*
|
||||
* Copyright 2019 Google LLC
|
||||
*/
|
||||
|
|
@ -32,8 +32,8 @@ static struct key *fsverity_keyring;
|
|||
* @desc: the file's fsverity_descriptor
|
||||
* @desc_size: size of @desc
|
||||
*
|
||||
* If the file's fs-verity descriptor includes a signature of the file
|
||||
* measurement, verify it against the certificates in the fs-verity keyring.
|
||||
* If the file's fs-verity descriptor includes a signature of the file digest,
|
||||
* verify it against the certificates in the fs-verity keyring.
|
||||
*
|
||||
* Return: 0 on success (signature valid or not required); -errno on failure
|
||||
*/
|
||||
|
|
@ -44,7 +44,7 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
|
|||
const struct inode *inode = vi->inode;
|
||||
const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg;
|
||||
const u32 sig_size = le32_to_cpu(desc->sig_size);
|
||||
struct fsverity_signed_digest *d;
|
||||
struct fsverity_formatted_digest *d;
|
||||
int err;
|
||||
|
||||
if (sig_size == 0) {
|
||||
|
|
@ -67,7 +67,7 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
|
|||
memcpy(d->magic, "FSVerity", 8);
|
||||
d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs);
|
||||
d->digest_size = cpu_to_le16(hash_alg->digest_size);
|
||||
memcpy(d->digest, vi->measurement, hash_alg->digest_size);
|
||||
memcpy(d->digest, vi->file_digest, hash_alg->digest_size);
|
||||
|
||||
err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
|
||||
desc->signature, sig_size,
|
||||
|
|
@ -90,8 +90,8 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
|
|||
return err;
|
||||
}
|
||||
|
||||
pr_debug("Valid signature for file measurement %s:%*phN\n",
|
||||
hash_alg->name, hash_alg->digest_size, vi->measurement);
|
||||
pr_debug("Valid signature for file digest %s:%*phN\n",
|
||||
hash_alg->name, hash_alg->digest_size, vi->file_digest);
|
||||
return 0;
|
||||
}
|
||||
|
||||
|
|
|
|||
|
|
@ -1,6 +1,6 @@
|
|||
// SPDX-License-Identifier: GPL-2.0
|
||||
/*
|
||||
* fs/verity/verify.c: data verification functions, i.e. hooks for ->readpages()
|
||||
* Data verification functions, i.e. hooks for ->readpages()
|
||||
*
|
||||
* Copyright 2019 Google LLC
|
||||
*/
|
||||
|
|
|
|||
|
|
@ -34,6 +34,55 @@ struct fsverity_digest {
|
|||
__u8 digest[];
|
||||
};
|
||||
|
||||
/*
|
||||
* Struct containing a file's Merkle tree properties. The fs-verity file digest
|
||||
* is the hash of this struct. A userspace program needs this struct only if it
|
||||
* needs to compute fs-verity file digests itself, e.g. in order to sign files.
|
||||
* It isn't needed just to enable fs-verity on a file.
|
||||
*
|
||||
* Note: when computing the file digest, 'sig_size' and 'signature' must be left
|
||||
* zero and empty, respectively. These fields are present only because some
|
||||
* filesystems reuse this struct as part of their on-disk format.
|
||||
*/
|
||||
struct fsverity_descriptor {
|
||||
__u8 version; /* must be 1 */
|
||||
__u8 hash_algorithm; /* Merkle tree hash algorithm */
|
||||
__u8 log_blocksize; /* log2 of size of data and tree blocks */
|
||||
__u8 salt_size; /* size of salt in bytes; 0 if none */
|
||||
#ifdef __KERNEL__
|
||||
__le32 sig_size;
|
||||
#else
|
||||
__le32 __reserved_0x04; /* must be 0 */
|
||||
#endif
|
||||
__le64 data_size; /* size of file the Merkle tree is built over */
|
||||
__u8 root_hash[64]; /* Merkle tree root hash */
|
||||
__u8 salt[32]; /* salt prepended to each hashed block */
|
||||
__u8 __reserved[144]; /* must be 0's */
|
||||
#ifdef __KERNEL__
|
||||
__u8 signature[];
|
||||
#endif
|
||||
};
|
||||
|
||||
/*
|
||||
* Format in which fs-verity file digests are signed in built-in signatures.
|
||||
* This is the same as 'struct fsverity_digest', except here some magic bytes
|
||||
* are prepended to provide some context about what is being signed in case the
|
||||
* same key is used for non-fsverity purposes, and here the fields have fixed
|
||||
* endianness.
|
||||
*
|
||||
* This struct is specific to the built-in signature verification support, which
|
||||
* is optional. fs-verity users may also verify signatures in userspace, in
|
||||
* which case userspace is responsible for deciding on what bytes are signed.
|
||||
* This struct may still be used, but it doesn't have to be. For example,
|
||||
* userspace could instead use a string like "sha256:$digest_as_hex_string".
|
||||
*/
|
||||
struct fsverity_formatted_digest {
|
||||
char magic[8]; /* must be "FSVerity" */
|
||||
__le16 digest_algorithm;
|
||||
__le16 digest_size;
|
||||
__u8 digest[];
|
||||
};
|
||||
|
||||
#define FS_IOC_ENABLE_VERITY _IOW('f', 133, struct fsverity_enable_arg)
|
||||
#define FS_IOC_MEASURE_VERITY _IOWR('f', 134, struct fsverity_digest)
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue