kernel: add su compat mode

kernel/sucompat.c

@@ -0,0 +1,135 @@
+
+#include <linux/cpu.h>
+#include <linux/memory.h>
+#include <linux/uaccess.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/printk.h>
+#include <linux/string.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <asm-generic/errno-base.h>
+
+#include <linux/rcupdate.h>
+#include <linux/fdtable.h>
+#include <linux/fs.h> 
+#include <linux/fs_struct.h>
+#include <linux/namei.h>
+
+#include "klog.h"
+#include "arch.h"
+#include "allowlist.h"
+
+#define SU_PATH "/system/bin/su"
+#define SH_PATH "/system/bin/sh"
+
+extern void escape_to_root(bool);
+
+static void __user *userspace_stack_buffer(const void *d, size_t len) {
+	/* To avoid having to mmap a page in userspace, just write below the stack pointer. */
+	char __user *p = (void __user *)current_user_stack_pointer() - len;
+
+	return copy_to_user(p, d, len) ? NULL : p;
+}
+
+static char __user *sh_user_path(void) {
+	static const char sh_path[] = "/system/bin/sh";
+
+	return userspace_stack_buffer(sh_path, sizeof(sh_path));
+}
+
+static int faccessat_handler_pre(struct kprobe *p, struct pt_regs *regs) {
+    struct filename* filename;
+    const char su[] = SU_PATH;
+
+    if (!ksu_is_allow_uid(current_uid().val)) {
+        return 0;
+    }
+
+    filename = getname(PT_REGS_PARM2(regs));
+
+    if (IS_ERR(filename)) {
+        return 0;
+    }
+    if (!memcmp(filename->name, su, sizeof(su))) {
+        pr_info("faccessat su->sh!\n");
+        regs->regs[1] = sh_user_path();
+    }
+
+    return 0;
+}
+
+static int newfstatat_handler_pre(struct kprobe *p, struct pt_regs *regs) {
+    // const char sh[] = SH_PATH;
+    struct filename* filename;
+    const char su[] = SU_PATH;
+
+    if (!ksu_is_allow_uid(current_uid().val)) {
+        return 0;
+    }
+
+    filename = getname(PT_REGS_PARM2(regs));
+
+    if (IS_ERR(filename)) {
+        return 0;
+    }
+    if (!memcmp(filename->name, su, sizeof(su))) {
+        pr_info("newfstatat su->sh!\n");
+        regs->regs[1] = sh_user_path();
+    }
+
+    return 0;
+}
+
+// https://elixir.bootlin.com/linux/v5.10.158/source/fs/exec.c#L1864
+static int execve_handler_pre(struct kprobe *p, struct pt_regs *regs) { 
+    struct filename* filename;
+    const char sh[] = SH_PATH;
+    const char su[] = SU_PATH;
+
+    if (!ksu_is_allow_uid(current_uid().val)) {
+        return 0;
+    }
+
+    filename = PT_REGS_PARM2(regs);
+    if (IS_ERR(filename)) {
+        return 0;
+    }
+
+    if (!memcmp(filename->name, su, sizeof(su))) { 
+        pr_info("do_execveat_common su found\n");
+        memcpy((void*) filename->name, sh, sizeof(sh));
+
+        escape_to_root(false);
+    }
+
+    return 0;
+}
+
+static struct kprobe faccessat_kp = {
+    .symbol_name = "do_faccessat",
+    .pre_handler = faccessat_handler_pre,
+};
+
+static struct kprobe newfstatat_kp = {
+    .symbol_name = "vfs_statx",
+    .pre_handler = newfstatat_handler_pre,
+};
+
+static struct kprobe execve_kp = {
+    .symbol_name = "do_execveat_common",
+    .pre_handler = execve_handler_pre,
+};
+
+// sucompat: permited process can execute 'su' to gain root access.
+void enable_sucompat() {
+    int ret;
+
+    ret = register_kprobe(&execve_kp);
+    pr_info("execve_kp: %d\n", ret);
+    ret = register_kprobe(&newfstatat_kp);
+    pr_info("newfstatat_kp: %d\n", ret);
+    ret = register_kprobe(&faccessat_kp);
+    pr_info("faccessat_kp: %d\n", ret);
+}