Start android 10 proot wrapping experiment

Author: fornwall

termux-exec.c

@@ -1,6 +1,9 @@
 #include <dlfcn.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
+#include <limits.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -21,6 +24,16 @@ static const char* termux_rewrite_executable(const char* filename, char* buffer,
 
 int execve(const char* filename, char* const* argv, char *const envp[])
 {
+	bool android_10_debug = getenv("TERMUX_ANDROID10_DEBUG") != NULL;
+	if (android_10_debug) {
+		printf("execve(%s):\n", filename);
+		int tmp_argv_count = 0;
+		while (argv[tmp_argv_count] != NULL) {
+			printf("  %s\n", argv[tmp_argv_count]);
+			tmp_argv_count++;
+		}
+	}
+
 	int fd = -1;
 	const char** new_argv = NULL;
 
@@ -92,6 +105,64 @@ int execve(const char* filename, char* const* argv, char *const envp[])
 final:
 	if (fd != -1) close(fd);
 	int (*real_execve)(const char*, char *const[], char *const[]) = dlsym(RTLD_NEXT, "execve");
+
+	bool android_10_wrapping = getenv("TERMUX_ANDROID10") != NULL;
+	if (android_10_wrapping) {
+		char realpath_buffer[PATH_MAX];
+		bool realpath_ok = realpath(filename, realpath_buffer) != NULL;
+		if (realpath_ok) {
+			bool wrap_in_proot = (strstr(realpath_buffer, "/data/data/com.termux/files") != NULL);
+			if (android_10_debug) {
+				printf("termux-exec: realpath(\"%s\") = \"%s\", wrapping=%s\n", filename, realpath_buffer, wrap_in_proot ? "yes" : "no");
+			}
+			if (wrap_in_proot) {
+				orig_argv_count = 0;
+				while (argv[orig_argv_count] != NULL) orig_argv_count++;
+
+				new_argv = malloc(sizeof(char*) * (2 + orig_argv_count));
+				filename = "/data/data/com.termux/files/usr/bin/proot";
+				new_argv[0] = "proot";
+				for (int i = 0; i < orig_argv_count; i++) {
+					new_argv[i + 1] = argv[i];
+				}
+				new_argv[orig_argv_count + 1] = NULL;
+				argv = (char**) new_argv;
+
+				// Remove LD_PRELOAD environment variable when wrapping in proot:
+				for (int i = 0; envp[i] != NULL; i++) {
+					if (strstr(envp[i], "LD_PRELOAD=") == envp[i]) {
+						int env_length = 0;
+						while (envp[env_length] != NULL) env_length++;
+
+						char** new_envp = malloc(sizeof(char*) * env_length);
+						int new_envp_idx = 0;
+						int old_envp_idx = 0;
+						while (old_envp_idx < env_length) {
+							if (old_envp_idx != i) {
+								new_envp[new_envp_idx++] = envp[old_envp_idx];
+							}
+							old_envp_idx++;
+						}
+						new_envp[env_length] = NULL;
+						envp = new_envp;
+						break;
+					}
+				}
+			}
+		} else {
+			errno = 0;
+		}
+
+		if (android_10_debug) {
+			printf("real_execve(%s):\n", filename);
+			int tmp_argv_count = 0;
+			while (argv[tmp_argv_count] != NULL) {
+				printf("  %s\n", argv[tmp_argv_count]);
+				tmp_argv_count++;
+			}
+		}
+	}
+
 	int ret = real_execve(filename, argv, envp);
 	free(new_argv);
 	return ret;