Read certificate in Rust

Co-authored-by: topjohnwu <topjohnwu@gmail.com>

native/src/Android.mk

@@ -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 \

native/src/base/misc.rs

@@ -288,27 +288,30 @@ pub unsafe fn slice_from_ptr_mut<'a, T>(buf: *mut T, len: usize) -> &'a mut [T]
     }
 }
 
-pub trait FlatData {
+pub trait FlatData
-    fn as_raw_bytes(&self) -> &[u8]
+where
-    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]
+    fn as_raw_bytes_mut(&mut self) -> &mut [u8] {
-    where
-        Self: Sized,
-    {
         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 {
     fn is_error(&self) -> bool;

native/src/core/cert.cpp

@@ -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 {};
-}

native/src/core/cert.rs

@@ -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![])
+}

native/src/core/core.hpp

@@ -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();

native/src/core/lib.rs

@@ -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;

native/src/core/package.cpp

@@ -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