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Mock selinuxfs load with regular file

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The hijacked load node does not need to be a FIFO. A FIFO is only
required for blocking init's control flow, which is already achieved
by hijacking the enforce node.
This commit is contained in:
topjohnwu 2022-04-16 07:27:34 -07:00
parent c2b74aa83e
commit 134508193d
2 changed files with 10 additions and 25 deletions
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8
native/jni/core/daemon.cpp
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@ -362,14 +362,6 @@ static void daemon_entry() {
}
rm_rf((MAGISKTMP + "/" ROOTOVL).data());
// SELinux mock cleanups
string selinux_mock = MAGISKTMP + "/" SELINUXMOCK;
string fs = selinux_mock + "/fs";
if (access(fs.data(), F_OK) == 0) {
umount2(fs.data(), MNT_DETACH);
}
rm_rf(selinux_mock.data());
// Load config status
auto config = MAGISKTMP + "/" INTLROOT "/config";
parse_prop_file(config.data(), [](auto key, auto val) -> bool {

27
native/jni/init/selinux.cpp
View File

@ -40,7 +40,6 @@ void MagiskInit::patch_sepolicy(const char *in, const char *out) {
#define MOCK_COMPAT SELINUXMOCK "/compatible"
#define MOCK_LOAD SELINUXMOCK "/load"
#define MOCK_ENFORCE SELINUXMOCK "/enforce"
#define REAL_SELINUXFS SELINUXMOCK "/fs"
bool MagiskInit::hijack_sepolicy() {
xmkdir(SELINUXMOCK, 0);
@ -58,7 +57,7 @@ bool MagiskInit::hijack_sepolicy() {
// the actual sepolicy being loaded into the kernel
auto hijack = [&] {
LOGD("Hijack [" SELINUX_LOAD "]\n");
mkfifo(MOCK_LOAD, 0600);
close(xopen(MOCK_LOAD, O_CREAT | O_RDONLY, 0600));
xmount(MOCK_LOAD, SELINUX_LOAD, nullptr, MS_BIND, nullptr);
LOGD("Hijack [" SELINUX_ENFORCE "]\n");
mkfifo(MOCK_ENFORCE, 0644);
@ -131,28 +130,21 @@ bool MagiskInit::hijack_sepolicy() {
close(fd);
}
// Read full sepolicy
int fd = xopen(MOCK_LOAD, O_RDONLY);
string policy = fd_full_read(fd);
close(fd);
auto sepol = unique_ptr<sepolicy>(sepolicy::from_data(policy.data(), policy.length()));
sepol->magisk_rules();
sepol->load_rules(rules);
// This open will block until init calls security_getenforce
fd = xopen(MOCK_ENFORCE, O_WRONLY);
int fd = xopen(MOCK_ENFORCE, O_WRONLY);
// Cleanup the hijacks
umount2("/init", MNT_DETACH);
xumount2(SELINUX_LOAD, MNT_DETACH);
xumount2(SELINUX_ENFORCE, MNT_DETACH);
// Load patched policy
xmkdir(REAL_SELINUXFS, 0755);
xmount("selinuxfs", REAL_SELINUXFS, "selinuxfs", 0, nullptr);
sepol->to_file(REAL_SELINUXFS "/load");
string enforce = full_read(SELINUX_ENFORCE);
// Load and patch policy
auto sepol = unique_ptr<sepolicy>(sepolicy::from_file(MOCK_LOAD));
sepol->magisk_rules();
sepol->load_rules(rules);
// Load patched policy into kernel
sepol->to_file(SELINUX_LOAD);
// Write to the enforce node ONLY after sepolicy is loaded. We need to make sure
// the actual init process is blocked until sepolicy is loaded, or else
@ -161,6 +153,7 @@ bool MagiskInit::hijack_sepolicy() {
// it has been replaced with our FIFO file, init will block until we
// write something into the pipe, effectively hijacking its control flow.
string enforce = full_read(SELINUX_ENFORCE);
xwrite(fd, enforce.data(), enforce.length());
close(fd);