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47 lines
1.8 KiB
47 lines
1.8 KiB
/*
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* Copyright (C) 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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use anyhow::{bail, Result};
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use libc::getxattr;
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use std::ffi::CString;
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use std::io;
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use std::os::unix::io::{AsRawFd, BorrowedFd};
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const SHA256_HASH_SIZE: usize = 32;
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/// Bytes of SHA256 digest
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pub type Sha256Digest = [u8; SHA256_HASH_SIZE];
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/// Returns the fs-verity measurement/digest. Currently only SHA256 is supported.
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pub fn measure(fd: BorrowedFd) -> Result<Sha256Digest> {
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// TODO(b/196635431): Unfortunately, the FUSE API doesn't allow authfs to implement the standard
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// fs-verity ioctls. Until the kernel allows, use the alternative xattr that authfs provides.
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let path = CString::new(format!("/proc/self/fd/{}", fd.as_raw_fd()).as_str()).unwrap();
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let name = CString::new("authfs.fsverity.digest").unwrap();
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let mut buf = [0u8; SHA256_HASH_SIZE];
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// SAFETY: getxattr should not write beyond the given buffer size.
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let size = unsafe {
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getxattr(path.as_ptr(), name.as_ptr(), buf.as_mut_ptr() as *mut libc::c_void, buf.len())
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};
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if size < 0 {
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bail!("Failed to getxattr: {}", io::Error::last_os_error());
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} else if size != SHA256_HASH_SIZE as isize {
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bail!("Unexpected hash size: {}", size);
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} else {
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Ok(buf)
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}
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}
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