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fix(dalvikvm): bypass W^X restriction #138

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fix(dalvikvm): bypass W^X restriction #138

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1 change: 1 addition & 0 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ AM_INIT_AUTOMAKE([foreign])
AC_PROG_MAKE_SET
AC_PROG_CC
AC_LANG(C)
LT_INIT

copyright="Copyright (C) 2022-2024 Termux."
if test "${TERMUX_APP_PACKAGE+set}" = set; then
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1 change: 1 addition & 0 deletions scripts/dalvikvm.in
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Expand Up @@ -11,4 +11,5 @@ else
fi

unset LD_LIBRARY_PATH LD_PRELOAD
export LD_PRELOAD=@TERMUX_PREFIX@/lib/termux/libtermux-access.so
exec "$DALVIKVM" -Xusejit:true -Xnoimage-dex2oat -Djava.io.tmpdir=@TERMUX_PREFIX@/tmp "$@"
10 changes: 10 additions & 0 deletions src/Makefile.am
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Expand Up @@ -21,3 +21,13 @@ AM_CFLAGS = -Wall -Wextra -pedantic
bin_PROGRAMS = cmd

cmd_SOURCES = cmd.c

libdir = $(prefix)/lib/termux

lib_LTLIBRARIES = libtermux-access.la

libtermux_access_la_SOURCES = termux_access.c
libtermux_access_la_LDFLAGS = -shared -module -avoid-version -ldl

clean-local:
rm -f libtermux-access.la
37 changes: 37 additions & 0 deletions src/termux_access.c
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@@ -0,0 +1,37 @@
#define _GNU_SOURCE
#include <dlfcn.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>

// This library is needed to bypass W^X restriction in Dalvik code.
// https://cs.android.com/android/platform/superproject/+/dd6fde63193fda968440fc0a4cd9ccee5d282ab0:art/runtime/native/dalvik_system_DexFile.cc;l=381

static int stub_access(const char* __unused path, int __unused mode) {
return -1;
}

// Function pointer for the original access function
static int (*orig_access)(const char *path, int mode) = stub_access;

// Constructor to load the original access function
__attribute__((constructor, visibility("hidden")))
static void load_orig_access(void) {
orig_access = (int (*)(const char *, int))dlsym(RTLD_NEXT, "access");
if (orig_access == NULL) {
dprintf(2, "Error in `dlsym`: %s\n", dlerror());
orig_access = stub_access;
}
}

int access(const char *path, int mode) {
// Checking if path ends with ".apk", if ".apk" is an extension and if mode is W_OK
const char *apk = path == NULL ? NULL : strstr(path, ".apk");
if (mode == W_OK && apk != NULL && !strcmp(apk, ".apk"))
return 1;

// Call the original access function for other cases
return orig_access(path, mode);
}