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# T2 SDE: package/*/qemu/chroot.patch
# Copyright (C) 2022 - 2023 The T2 SDE Project
# 
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Quick and dirty patch for qemu user emulation how to chroot and drop
priveledges, so you don't have to clutter a target filesystem with host code,
figure out how to build qemu static in order to run a dynamic binary, or set
Linux binfmt.

  - Rene Rebe <rene@exactcode.de>

--- qemu-8.0.0/linux-user/main.c.vanilla	2023-04-20 12:20:12.493209854 +0200
+++ qemu-8.0.0/linux-user/main.c	2023-04-20 12:22:14.849197124 +0200
@@ -422,6 +422,32 @@
 }
 #endif
 
+static void handle_arg_chroot(const char* arg)
+{
+    if (chdir(arg) || chroot(".")) {
+	fprintf(stderr, "Can't chroot into '%s'\n", arg);
+	_exit(1);
+    }
+}
+
+static void handle_arg_su(const char* arg)
+{
+    int temp;
+    char *gid = strchr(arg, ':');
+    if (gid) {
+	temp = atoi(++gid);
+	if (setresgid(temp, temp, temp)) {
+	    fprintf(stderr, "Can't set gid to %d\n", temp);
+	    _exit(1);
+        }
+    }
+    temp = atoi(arg);
+    if (setresuid(temp, temp, temp)) {
+        fprintf(stderr, "Can't set uid to %d\n", temp);
+        _exit(1);
+    }
+}
+
 struct qemu_argument {
     const char *argv;
     const char *env;
@@ -548,6 +548,10 @@
      "",           "Generate a /tmp/perf-${pid}.map file for perf"},
     {"jitdump",    "QEMU_JITDUMP",     false, handle_arg_jitdump,
      "",           "Generate a jit-${pid}.dump file for perf"},
+    {"chroot",     "",                 true,  handle_arg_chroot,
+     "",           "chroot into dir"},
+    {"su",         "",                 true,  handle_arg_su,
+     "",           "set numeric user and group IDs"},
     {NULL, NULL, false, NULL, NULL, NULL}
 };