Changes to companion fork

snake-4 · May 7, 2024 · 9c06b69 · 9c06b69
1 parent 6530a5a
commit 9c06b69
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Showing 3 changed files with 26 additions and 34 deletions.
diff --git a/module/jni/include/utils.hpp b/module/jni/include/utils.hpp
@@ -35,5 +35,5 @@ namespace Utils
     bool switchMountNS(int pid);
     int isUserAppUID(int uid);
     bool hookPLTByName(zygisk::Api *api, const std::string &libName, const std::string &symbolName, void *hookFunc, void **origFunc);
-    int executeLambdaInFork(const std::function<void()> &lambda);
+    int forkAndInvoke(const std::function<int()> &lambda);
 }
diff --git a/module/jni/main.cpp b/module/jni/main.cpp
@@ -155,23 +155,20 @@ class ZygiskModule : public zygisk::ModuleBase
 
 void zygisk_companion_handler(int fd)
 {
-    bool result = [&]() -> bool
-    {
-        pid_t pid;
-        ASSERT_DO(zygisk_companion_handler, read(fd, &pid, sizeof(pid)) == sizeof(pid), return false);
-        ASSERT_DO(zygisk_companion_handler, unshare(CLONE_NEWNS) != -1, return false);
-        ASSERT_DO(zygisk_companion_handler, Utils::switchMountNS(pid), return false);
-        LOGD("zygisk_companion_handler processing namespace of pid=%d", pid);
-
-        // setns mount namespace is not effective until a fork(?)
-        return WIFEXITED(Utils::executeLambdaInFork(
-            []()
-            {
-                doUnmount();
-                doRemount();
-                doMrProp();
-            }));
-    }();
+    pid_t pid;
+    ASSERT_DO(zygisk_companion_handler, read(fd, &pid, sizeof(pid)) == sizeof(pid), return);
+    LOGD("zygisk_companion_handler processing namespace of pid=%d", pid);
+
+    // setns requires the caller to be single-threaded
+    bool result = WIFEXITED(Utils::forkAndInvoke(
+        [pid]()
+        {
+            ASSERT_DO(zygisk_companion_handler, Utils::switchMountNS(pid), return 1);
+            doUnmount();
+            doRemount();
+            doMrProp();
+            return 0;
+        }));
 
     ASSERT_LOG(zygisk_companion_handler, write(fd, &result, sizeof(result)) == sizeof(result));
 }

diff --git a/module/jni/utils.cpp b/module/jni/utils.cpp
@@ -56,7 +56,7 @@ bool Utils::switchMountNS(int pid)
 {
     std::string path = "/proc/" + std::to_string(pid) + "/ns/mnt";
     int ret, fd;
-    if ((fd = open(path.c_str(), O_RDONLY)) < 0)
+    if ((fd = open(path.c_str(), O_RDONLY | O_CLOEXEC)) < 0)
     {
         return false;
     }
@@ -66,22 +66,17 @@ bool Utils::switchMountNS(int pid)
     return ret == 0;
 }
 
-int Utils::executeLambdaInFork(const std::function<void()> &lambda)
+int Utils::forkAndInvoke(const std::function<int()> &lambda)
 {
     pid_t pid = fork();
-    ASSERT_DO(executeLambdaInFork, pid != -1, return -1);
+    if (pid == -1)
+        return -1;
 
-    if (pid == 0)
-    {
-        // Child process
-        lambda();
-        exit(EXIT_SUCCESS);
-    }
-    else
-    {
-        // Parent process
-        int status = -1;
-        waitpid(pid, &status, 0);
-        return status;
-    }
+    if (pid == 0) // Child process
+        exit(lambda());
+
+    // Parent process
+    int status = -1;
+    waitpid(pid, &status, 0);
+    return status;
 }