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Read certificate in Rust

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Co-authored-by: topjohnwu <topjohnwu@gmail.com>
This commit is contained in:
LoveSy 2023-06-14 22:24:42 +08:00 committed by John Wu
parent d2eaa6e6c1
commit a9c89cbbbb
7 changed files with 173 additions and 224 deletions
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1
native/src/Android.mk
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@ -25,7 +25,6 @@ LOCAL_SRC_FILES := \
core/socket.cpp \
core/db.cpp \
core/package.cpp \
core/cert.cpp \
core/scripting.cpp \
core/restorecon.cpp \
core/module.cpp \

15
native/src/base/misc.rs
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@ -288,26 +288,29 @@ pub unsafe fn slice_from_ptr_mut<'a, T>(buf: *mut T, len: usize) -> &'a mut [T]
}
}
pub trait FlatData {
fn as_raw_bytes(&self) -> &[u8]
pub trait FlatData
where
Self: Sized,
{
fn as_raw_bytes(&self) -> &[u8] {
unsafe {
let self_ptr = self as *const Self as *const u8;
slice::from_raw_parts(self_ptr, std::mem::size_of::<Self>())
}
}
fn as_raw_bytes_mut(&mut self) -> &mut [u8]
where
Self: Sized,
{
fn as_raw_bytes_mut(&mut self) -> &mut [u8] {
unsafe {
let self_ptr = self as *mut Self as *mut u8;
slice::from_raw_parts_mut(self_ptr, std::mem::size_of::<Self>())
}
}
fn bytes_size(&self) -> usize {
std::mem::size_of::<Self>()
}
}
impl<T: Copy> FlatData for T {}
// Check libc return value and map errors to Result
pub trait LibcReturn: Copy {

208
native/src/core/cert.cpp
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@ -1,208 +0,0 @@
#include <base.hpp>
using namespace std;
#define APK_SIGNING_BLOCK_MAGIC "APK Sig Block 42"
#define SIGNATURE_SCHEME_V2_MAGIC 0x7109871a
#define EOCD_MAGIC 0x6054b50
// Top-level block container
struct signing_block {
uint64_t block_sz;
struct id_value_pair {
uint64_t len;
struct /* v2_signature */ {
uint32_t id;
uint8_t value[0]; // size = (len - 4)
};
} id_value_pair_sequence[0];
uint64_t block_sz_; // *MUST* be same as block_sz
char magic[16]; // "APK Sig Block 42"
};
struct len_prefixed {
uint32_t len;
};
// Generic length prefixed raw data
struct len_prefixed_value : public len_prefixed {
uint8_t value[0];
};
// V2 Signature Block
struct v2_signature {
uint32_t id; // 0x7109871a
uint32_t signer_sequence_len;
struct signer : public len_prefixed {
struct signed_data : public len_prefixed {
uint32_t digest_sequence_len;
struct : public len_prefixed {
uint32_t algorithm;
len_prefixed_value digest;
} digest_sequence[0];
uint32_t certificate_sequence_len;
len_prefixed_value certificate_sequence[0];
uint32_t attribute_sequence_len;
struct attribute : public len_prefixed {
uint32_t id;
uint8_t value[0]; // size = (len - 4)
} attribute_sequence[0];
} signed_data;
uint32_t signature_sequence_len;
struct : public len_prefixed {
uint32_t id;
len_prefixed_value signature;
} signature_sequence[0];
len_prefixed_value public_key;
} signer_sequence[0];
};
// End of central directory record
struct EOCD {
uint32_t magic; // 0x6054b50
uint8_t pad[8]; // 8 bytes of irrelevant data
uint32_t central_dir_sz; // size of central directory
uint32_t central_dir_off; // offset of central directory
uint16_t comment_sz; // size of comment
char comment[0];
} __attribute__((packed));
/*
* A v2/v3 signed APK has the format as following
*
* +---------------+
* | zip content |
* +---------------+
* | signing block |
* +---------------+
* | central dir |
* +---------------+
* | EOCD |
* +---------------+
*
* Scan from end of file to find EOCD, and figure our way back to the
* offset of the signing block. Next, directly extract the certificate
* from the v2 signature block.
*
* All structures above are mostly just for documentation purpose.
*
* This method extracts the first certificate of the first signer
* within the APK v2 signature block.
*/
string read_certificate(int fd, int version) {
uint32_t u32;
uint64_t u64;
// Find EOCD
for (int i = 0;; i++) {
// i is the absolute offset to end of file
uint16_t comment_sz = 0;
xlseek64(fd, -static_cast<off64_t>(sizeof(comment_sz)) - i, SEEK_END);
xxread(fd, &comment_sz, sizeof(comment_sz));
if (comment_sz == i) {
// Double check if we actually found the structure
xlseek64(fd, -static_cast<off64_t>(sizeof(EOCD)), SEEK_CUR);
uint32_t magic = 0;
xxread(fd, &magic, sizeof(magic));
if (magic == EOCD_MAGIC) {
break;
}
}
if (i == 0xffff) {
// Comments cannot be longer than 0xffff (overflow), abort
LOGE("cert: invalid APK format\n");
return {};
}
}
// We are now at EOCD + sizeof(magic)
// Seek and read central_dir_off to find start of central directory
uint32_t central_dir_off = 0;
{
constexpr off64_t off = offsetof(EOCD, central_dir_off) - sizeof(EOCD::magic);
xlseek64(fd, off, SEEK_CUR);
}
xxread(fd, &central_dir_off, sizeof(central_dir_off));
// Parse APK comment to get version code
if (version >= 0) {
xlseek64(fd, sizeof(EOCD::comment_sz), SEEK_CUR);
FILE *fp = fdopen(fd, "r"); // DO NOT close this file pointer
int apk_ver = -1;
parse_prop_file(fp, [&](string_view key, string_view value) -> bool {
if (key == "versionCode") {
apk_ver = parse_int(value);
return false;
}
return true;
});
if (version > apk_ver) {
// Enforce the magisk app to always be newer than magiskd
LOGE("cert: APK version too low\n");
return {};
}
}
// Next, find the start of the APK signing block
{
constexpr int off = sizeof(signing_block::block_sz_) + sizeof(signing_block::magic);
xlseek64(fd, (off64_t) (central_dir_off - off), SEEK_SET);
}
xxread(fd, &u64, sizeof(u64)); // u64 = block_sz_
char magic[sizeof(signing_block::magic)] = {0};
xxread(fd, magic, sizeof(magic));
if (memcmp(magic, APK_SIGNING_BLOCK_MAGIC, sizeof(magic)) != 0) {
// Invalid signing block magic, abort
LOGE("cert: invalid signing block magic\n");
return {};
}
uint64_t signing_blk_sz = 0;
xlseek64(fd, -static_cast<off64_t>(u64 + sizeof(signing_blk_sz)), SEEK_CUR);
xxread(fd, &signing_blk_sz, sizeof(signing_blk_sz));
if (signing_blk_sz != u64) {
// block_sz != block_sz_, invalid signing block format, abort
LOGE("cert: invalid signing block format\n");
return {};
}
// Finally, we are now at the beginning of the id-value pair sequence
for (;;) {
xxread(fd, &u64, sizeof(u64)); // id-value pair length
if (u64 == signing_blk_sz) {
// Outside of the id-value pair sequence; actually reading block_sz_
break;
}
uint32_t id;
xxread(fd, &id, sizeof(id));
if (id == SIGNATURE_SCHEME_V2_MAGIC) {
// Skip [signer sequence length] + [1st signer length] + [signed data length]
xlseek64(fd, sizeof(uint32_t) * 3, SEEK_CUR);
xxread(fd, &u32, sizeof(u32)); // digest sequence length
xlseek64(fd, u32, SEEK_CUR); // skip all digests
xlseek64(fd, sizeof(uint32_t), SEEK_CUR); // cert sequence length
xxread(fd, &u32, sizeof(u32)); // 1st cert length
string cert;
cert.resize(u32);
xxread(fd, cert.data(), u32);
return cert;
} else {
// Skip this id-value pair
xlseek64(fd, u64 - sizeof(id), SEEK_CUR);
}
}
LOGE("cert: cannot find certificate\n");
return {};
}

144
native/src/core/cert.rs Normal file
View File

@ -0,0 +1,144 @@
use std::fs::File;
use std::io;
use std::io::{Read, Seek, SeekFrom};
use std::os::fd::{FromRawFd, RawFd};
use base::*;
const EOCD_MAGIC: u32 = 0x06054B50;
const APK_SIGNING_BLOCK_MAGIC: [u8; 16] = *b"APK Sig Block 42";
const SIGNATURE_SCHEME_V2_MAGIC: u32 = 0x7109871A;
macro_rules! bad_apk {
($msg:literal) => {
io::Error::new(io::ErrorKind::InvalidData, concat!("cert: ", $msg))
};
}
/*
* A v2/v3 signed APK has the format as following
*
* +---------------+
* | zip content |
* +---------------+
* | signing block |
* +---------------+
* | central dir |
* +---------------+
* | EOCD |
* +---------------+
*
* Scan from end of file to find EOCD, and figure our way back to the
* offset of the signing block. Next, directly extract the certificate
* from the v2 signature block.
*
* All structures above are mostly just for documentation purpose.
*
* This method extracts the first certificate of the first signer
* within the APK v2 signature block.
*/
pub fn read_certificate(fd: RawFd, version: i32) -> Vec<u8> {
fn inner(apk: &mut File, version: i32) -> Result<Vec<u8>, io::Error> {
let mut u32_value = 0u32;
let mut u64_value = 0u64;
// Find EOCD
for i in 0u16.. {
let mut comment_sz = 0u16;
apk.seek(SeekFrom::End(-(comment_sz.bytes_size() as i64) - i as i64))?;
apk.read_exact(comment_sz.as_raw_bytes_mut())?;
if comment_sz == i {
apk.seek(SeekFrom::Current(-22))?;
let mut magic = 0u32;
apk.read_exact(magic.as_raw_bytes_mut())?;
if magic == EOCD_MAGIC {
break;
}
}
if i == 0xffff {
return Err(bad_apk!("invalid APK format"));
}
}
// We are now at EOCD + sizeof(magic)
// Seek and read central_dir_off to find the start of the central directory
let mut central_dir_off = 0u32;
apk.seek(SeekFrom::Current(12))?;
apk.read_exact(central_dir_off.as_raw_bytes_mut())?;
// Code for parse APK comment to get version code
if version >= 0 {
let mut comment_sz = 0u16;
apk.read_exact(comment_sz.as_raw_bytes_mut())?;
let mut comment = vec![0u8; comment_sz as usize];
apk.read_exact(&mut comment)?;
let mut comment = io::Cursor::new(&comment);
let mut apk_ver = 0;
comment.foreach_props(|k, v| {
if k == "versionCode" {
apk_ver = v.trim().parse::<i32>().unwrap_or(0);
true
} else {
false
}
});
if version > apk_ver {
return Err(bad_apk!("APK version too low"));
}
}
// Next, find the start of the APK signing block
apk.seek(SeekFrom::Start((central_dir_off - 24) as u64))?;
apk.read_exact(u64_value.as_raw_bytes_mut())?; // u64_value = block_sz_
let mut magic = [0u8; 16];
apk.read_exact(magic.as_raw_bytes_mut())?;
if magic != APK_SIGNING_BLOCK_MAGIC {
return Err(bad_apk!("invalid signing block magic"));
}
let mut signing_blk_sz = 0u64;
apk.seek(SeekFrom::Current(
-(u64_value as i64) - (signing_blk_sz.bytes_size() as i64),
))?;
apk.read_exact(signing_blk_sz.as_raw_bytes_mut())?;
if signing_blk_sz != u64_value {
return Err(bad_apk!("invalid signing block size"));
}
// Finally, we are now at the beginning of the id-value pair sequence
loop {
apk.read_exact(u64_value.as_raw_bytes_mut())?; // id-value pair length
if u64_value == signing_blk_sz {
break;
}
let mut id = 0u32;
apk.read_exact(id.as_raw_bytes_mut())?;
if id == SIGNATURE_SCHEME_V2_MAGIC {
// Skip [signer sequence length] + [1st signer length] + [signed data length]
apk.seek(SeekFrom::Current((u32_value.bytes_size() * 3) as i64))?;
apk.read_exact(u32_value.as_raw_bytes_mut())?; // digest sequence length
apk.seek(SeekFrom::Current(u32_value as i64))?; // skip all digests
apk.seek(SeekFrom::Current(u32_value.bytes_size() as i64))?; // cert sequence length
apk.read_exact(u32_value.as_raw_bytes_mut())?; // 1st cert length
let mut cert = vec![0; u32_value as usize];
apk.read_exact(cert.as_mut())?;
return Ok(cert);
} else {
// Skip this id-value pair
apk.seek(SeekFrom::Current(
u64_value as i64 - (id.bytes_size() as i64),
))?;
}
}
Err(bad_apk!("cannot find certificate"))
}
inner(unsafe { &mut File::from_raw_fd(libc::dup(fd)) }, version)
.log()
.unwrap_or(vec![])
}

1
native/src/core/core.hpp
View File

@ -12,7 +12,6 @@ extern std::atomic<ino_t> pkg_xml_ino;
std::string find_preinit_device();
void unlock_blocks();
void reboot();
std::string read_certificate(int fd, int version = -1);
// Module stuffs
void handle_modules();

4
native/src/core/lib.rs
View File

@ -1,9 +1,12 @@
#![feature(format_args_nl)]
#![allow(clippy::missing_safety_doc)]
use base::Utf8CStr;
use cert::*;
use daemon::*;
use logging::*;
mod cert;
#[path = "../include/consts.rs"]
mod consts;
mod daemon;
@ -28,6 +31,7 @@ pub mod ffi {
extern "Rust" {
fn daemon_entry();
fn zygisk_entry();
fn read_certificate(fd: i32, version: i32) -> Vec<u8>;
type MagiskD;
fn get_magiskd() -> &'static MagiskD;

18
native/src/core/package.cpp
View File

@ -25,6 +25,11 @@ static string *mgr_cert;
static int stub_apk_fd = -1;
static const string *default_cert;
static string read_certificate(int fd, int version) {
auto cert = rust::read_certificate(fd, version);
return string{cert.begin(), cert.end()};
}
void check_pkg_refresh() {
struct stat st{};
if (stat("/data/system/packages.xml", &st) == 0 &&
@ -71,7 +76,9 @@ void preserve_stub_apk() {
string stub_path = MAGISKTMP + "/stub.apk";
stub_apk_fd = xopen(stub_path.data(), O_RDONLY | O_CLOEXEC);
unlink(stub_path.data());
default_cert = new string(read_certificate(stub_apk_fd));
auto cert = read_certificate(stub_apk_fd, -1);
if (!cert.empty())
default_cert = new string(std::move(cert));
lseek(stub_apk_fd, 0, SEEK_SET);
}
@ -107,7 +114,8 @@ int get_manager(int user_id, string *pkg, bool install) {
LOGW("pkg: no dyn APK, ignore\n");
return false;
}
bool mismatch = default_cert && read_certificate(dyn, MAGISK_VER_CODE) != *default_cert;
auto cert = read_certificate(dyn, MAGISK_VER_CODE);
bool mismatch = default_cert && cert != *default_cert;
close(dyn);
if (mismatch) {
LOGE("pkg: dyn APK signature mismatch: %s\n", app_path);
@ -172,12 +180,12 @@ int get_manager(int user_id, string *pkg, bool install) {
byte_array<PATH_MAX> apk;
find_apk_path(byte_view(str[SU_MANAGER]), apk);
int fd = xopen((const char *) apk.buf(), O_RDONLY | O_CLOEXEC);
string cert = read_certificate(fd);
auto cert = read_certificate(fd, -1);
close(fd);
// Verify validity
if (str[SU_MANAGER] == *mgr_pkg) {
if (app_id != mgr_app_id || cert != *mgr_cert) {
if (app_id != mgr_app_id || cert.empty() || cert != *mgr_cert) {
// app ID or cert should never change
LOGE("pkg: repackaged APK signature invalid: %s\n", apk.buf());
uninstall_pkg(mgr_pkg->data());
@ -226,7 +234,7 @@ int get_manager(int user_id, string *pkg, bool install) {
byte_array<PATH_MAX> apk;
find_apk_path(byte_view(JAVA_PACKAGE_NAME), apk);
int fd = xopen((const char *) apk.buf(), O_RDONLY | O_CLOEXEC);
string cert = read_certificate(fd, MAGISK_VER_CODE);
auto cert = read_certificate(fd, MAGISK_VER_CODE);
close(fd);
if (default_cert && cert != *default_cert) {
// Found APK with invalid signature, force replace with stub