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Refactor magic mount to support overlayfs

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Previously, magic mount creates its own mirror devices and mount
mirror mount points. With these mirror mount points, magic mount
can get the original files and directory trees. However, some
devices use overlayfs to modify some mount points, and thus after
magic mount, the overlayed files are missing because the mirror
mount points do not contain the overlayed files. To address this
issue and make magic mount more compatible, this patch refactors
how magic mount works.

The new workflows are as follows:
1. make MAGISKTMP a private mount point so that we can create the
   private mount points there
2. for mirror mount points, we instead of creating our own mirror
   devices and mount the mirror mount points, we "copy" the
   original mount points by recursively mounting /
3. to prevent magic mount affecting the mirror mount points, we
   recursively set the mirror mount points private
4. to trace the mount points we created for reverting mounts, we
   again make the mirror mount points shared, and by this way we
   create a new peer group for each mirror mount points
5. as for tracing the newly created tmpfs mount point by magic
   mount, we create a dedicated tmpfs mount point for them, namely
   worker mount point, and obviously, it is shared as in a newly
   created peer group for tracing
6. when reverting mount points by magic mount, we can then trace
   the peer group id and unmount the mount points whose peer group
   ids are created by us

The advantages are as follows:
1. it is more compatible, (e.g., with overlayfs, fix #2359)
2. it can mount more partitions for which previous implementation
   cannot create mirror mount points (fix #3338)
This commit is contained in:
LoveSy 2022-12-27 04:30:12 +08:00 committed by John Wu
parent 97ed1b16d0
commit af01a36296
3 changed files with 52 additions and 109 deletions
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2
docs/guides.md
View File

@ -120,7 +120,7 @@ All files you want to replace/inject should be placed in this folder. This folde
If you place a file named `.replace` in any of the folders, instead of merging its contents, that folder will directly replace the one in the real system. This can be very handy for swapping out an entire folder.
If you want to replace files in `/vendor`, `/product`, or `/system_ext`, please place them under `system/vendor`, `system/product`, and `system/system_ext` respectively. Magisk will transparently handle whether these partitions are in a separate partition or not.
If you want to replace files in `/vendor`, `/vendor_dlkm`, `/product`, `/system_ext`, `/system_dlkm`, `/odm`, or `/odm_dlkm`, please place them under `system/vendor`, `system/product`, and `system/system_ext` respectively. Magisk will transparently handle whether these partitions are in a separate partition or not.
#### Zygisk

138
native/src/core/bootstages.cpp
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@ -1,6 +1,7 @@
#include <sys/mount.h>
#include <sys/wait.h>
#include <sys/sysmacros.h>
#include <sys/statvfs.h>
#include <linux/input.h>
#include <libgen.h>
#include <vector>
@ -34,103 +35,60 @@ bool zygisk_enabled = false;
* Setup *
*********/
#define MNT_DIR_IS(dir) (me->mnt_dir == string_view(dir))
#define MNT_TYPE_IS(type) (me->mnt_type == string_view(type))
#define SETMIR(b, part) ssprintf(b, sizeof(b), "%s/" MIRRDIR "/" #part, MAGISKTMP.data())
#define SETBLK(b, part) ssprintf(b, sizeof(b), "%s/" BLOCKDIR "/" #part, MAGISKTMP.data())
#define do_mount_mirror(part) { \
SETMIR(buf1, part); \
SETBLK(buf2, part); \
unlink(buf2); \
mknod(buf2, S_IFBLK | 0600, st.st_dev); \
xmkdir(buf1, 0755); \
int flags = 0; \
auto opts = split_ro(me->mnt_opts, ",");\
for (string_view s : opts) { \
if (s == "ro") { \
flags |= MS_RDONLY; \
break; \
} \
} \
xmount(buf2, buf1, me->mnt_type, flags, nullptr); \
LOGI("mount: %s\n", buf1); \
static bool mount_mirror(const std::string_view from, const std::string_view to) {
return !xmkdirs(to.data(), 0755) &&
// recursively bind mount to mirror dir, rootfs will fail before 3.12 kernel
// because of MS_NOUSER
!mount(from.data(), to.data(), nullptr, MS_BIND | MS_REC, nullptr) &&
// make mirror dir as a private mount so that it won't be affected by magic mount
!xmount("", to.data(), nullptr, MS_PRIVATE | MS_REC, nullptr);
}
#define mount_mirror(part) \
if (MNT_DIR_IS("/" #part) \
&& !MNT_TYPE_IS("tmpfs") \
&& !MNT_TYPE_IS("overlay") \
&& lstat(me->mnt_dir, &st) == 0) { \
do_mount_mirror(part); \
break; \
}
#define link_mirror(part) \
SETMIR(buf1, part); \
if (access("/system/" #part, F_OK) == 0 && access(buf1, F_OK) != 0) { \
xsymlink("./system/" #part, buf1); \
LOGI("link: %s\n", buf1); \
}
#define link_orig_dir(dir, part) \
if (MNT_DIR_IS(dir) && !MNT_TYPE_IS("tmpfs") && !MNT_TYPE_IS("overlay")) { \
SETMIR(buf1, part); \
rmdir(buf1); \
xsymlink(dir, buf1); \
LOGI("link: %s\n", buf1); \
break; \
}
#define link_orig(part) link_orig_dir("/" #part, part)
static void mount_mirrors() {
char buf1[4096];
char buf2[4096];
LOGI("* Prepare worker\n");
ssprintf(buf1, sizeof(buf1), "%s/" WORKERDIR, MAGISKTMP.data());
xmount(buf1, buf1, nullptr, MS_BIND, nullptr);
xmount(nullptr, buf1, nullptr, MS_PRIVATE, nullptr);
if (auto worker_dir = MAGISKTMP + "/" WORKERDIR;
xmount(worker_dir.data(), worker_dir.data(), nullptr, MS_BIND, nullptr) == 0) {
xmount(nullptr, worker_dir.data(), nullptr, MS_PRIVATE, nullptr);
}
LOGI("* Mounting mirrors\n");
// recursively bind mount / to mirror dir
if (auto mirror_dir = MAGISKTMP + "/" MIRRDIR; !mount_mirror("/", mirror_dir)) {
LOGI("fallback to mount subtree\n");
// rootfs may fail, fallback to bind mount each mount point
std::vector<string> mounted_dirs {{ MAGISKTMP }};
for (const auto &info: parse_mount_info("self")) {
if (info.type == "rootfs"sv) continue;
bool mounted = std::any_of(mounted_dirs.begin(), mounted_dirs.end(), [&](const auto &dir) {
return str_starts(info.target, dir);
});
if (!mounted && mount_mirror(info.target, mirror_dir + info.target)) {
mounted_dirs.emplace_back(info.target);
}
}
}
parse_mnt("/proc/mounts", [&](mntent *me) {
struct stat st{};
do {
mount_mirror(system)
mount_mirror(vendor)
mount_mirror(product)
mount_mirror(system_ext)
mount_mirror(data)
link_orig(cache)
link_orig(metadata)
link_orig(persist)
link_orig_dir("/mnt/vendor/persist", persist)
if (SDK_INT >= 24 && MNT_DIR_IS("/proc") && !strstr(me->mnt_opts, "hidepid=2")) {
xmount(nullptr, "/proc", nullptr, MS_REMOUNT, "hidepid=2,gid=3009");
LOGI("* Mounting module root\n");
if (access(SECURE_DIR, F_OK) == 0 || (SDK_INT < 24 && xmkdir(SECURE_DIR, 0700))) {
if (auto dest = MAGISKTMP + "/" MODULEMNT; mount_mirror(MODULEROOT, dest)) {
// remount to clear nosuid flag
struct statvfs st{};
statvfs(dest.data(), &st);
for (const auto &info: parse_mount_info("self")) {
if (info.target != dest) {
continue;
}
// strip rw, from fs options
if (auto pos = info.fs_option.find_first_of(','); pos != string::npos) {
xmount("", dest.data(), nullptr, MS_REMOUNT | (st.f_flag & ~MS_NOSUID), info.fs_option.data() + pos + 1);
}
break;
}
} while (false);
return true;
});
SETMIR(buf1, system);
if (access(buf1, F_OK) != 0) {
xsymlink("./system_root/system", buf1);
LOGI("link: %s\n", buf1);
parse_mnt("/proc/mounts", [&](mntent *me) {
struct stat st;
if (MNT_DIR_IS("/") && me->mnt_type != "rootfs"sv && stat("/", &st) == 0) {
do_mount_mirror(system_root)
return false;
restorecon();
chmod(SECURE_DIR, 0700);
}
return true;
});
}
link_mirror(vendor)
link_mirror(product)
link_mirror(system_ext)
}
static bool magisk_env() {
@ -306,17 +264,9 @@ static void post_fs_data() {
prune_su_access();
if (access(SECURE_DIR, F_OK) != 0) {
if (SDK_INT < 24) {
// There is no FBE pre 7.0, we can directly create the folder without issues
xmkdir(SECURE_DIR, 0700);
} else {
// If the folder is not automatically created by Android,
// do NOT proceed further. Manual creation of the folder
// will have no encryption flag, which will cause bootloops on FBE devices.
LOGE(SECURE_DIR " is not present, abort\n");
goto early_abort;
}
}
if (!magisk_env()) {
LOGE("* Magisk environment incomplete, abort\n");

15
native/src/core/module.cpp
View File

@ -32,7 +32,7 @@ class root_node;
template<class T> static bool isa(node_entry *node);
static int bind_mount(const char *reason, const char *from, const char *to) {
int ret = xmount(from, to, nullptr, MS_BIND, nullptr);
int ret = xmount(from, to, nullptr, MS_BIND | MS_REC, nullptr);
if (ret == 0)
VLOGD(reason, from, to);
return ret;
@ -623,7 +623,9 @@ void magic_mount() {
if (!system->is_empty()) {
// Handle special read-only partitions
for (const char *part : { "/vendor", "/product", "/system_ext" }) {
for (const char *part : { "/vendor", "/vendor_dlkm","/product",
"/system_ext", "/system_dlkm",
"/odm", "/odm_dlkm" }) {
struct stat st{};
if (lstat(part, &st) == 0 && S_ISDIR(st.st_mode)) {
if (auto old = system->extract(part + 1)) {
@ -669,15 +671,6 @@ static void prepare_modules() {
close(mfd);
rm_rf(MODULEUPGRADE);
}
// Setup module mount (workaround nosuid selabel issue)
auto src = MAGISKTMP + "/" MIRRDIR MODULEROOT;
auto dest = MAGISKTMP + "/" MODULEMNT;
xmkdir(dest.data(), 0755);
bind_mount("mod_mnt", src.data(), dest.data());
restorecon();
chmod(SECURE_DIR, 0700);
}
template<typename Func>