1 /*
2 * Copyright (C) 2021 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 use anyhow::{bail, Result};
18 use libc::getxattr;
19 use std::ffi::CString;
20 use std::io;
21 use std::os::unix::io::{AsRawFd, BorrowedFd};
22
23 const SHA256_HASH_SIZE: usize = 32;
24
25 /// Bytes of SHA256 digest
26 pub type Sha256Digest = [u8; SHA256_HASH_SIZE];
27
28 /// Returns the fs-verity measurement/digest. Currently only SHA256 is supported.
measure(fd: BorrowedFd) -> Result<Sha256Digest>29 pub fn measure(fd: BorrowedFd) -> Result<Sha256Digest> {
30 // TODO(b/196635431): Unfortunately, the FUSE API doesn't allow authfs to implement the standard
31 // fs-verity ioctls. Until the kernel allows, use the alternative xattr that authfs provides.
32 let path = CString::new(format!("/proc/self/fd/{}", fd.as_raw_fd()).as_str()).unwrap();
33 let name = CString::new("authfs.fsverity.digest").unwrap();
34 let mut buf = [0u8; SHA256_HASH_SIZE];
35 // SAFETY: getxattr should not write beyond the given buffer size.
36 let size = unsafe {
37 getxattr(path.as_ptr(), name.as_ptr(), buf.as_mut_ptr() as *mut libc::c_void, buf.len())
38 };
39 if size < 0 {
40 bail!("Failed to getxattr: {}", io::Error::last_os_error());
41 } else if size != SHA256_HASH_SIZE as isize {
42 bail!("Unexpected hash size: {}", size);
43 } else {
44 Ok(buf)
45 }
46 }
47