win32: changes to user ids

Formalise the use of 0 as the uid of a process running with elevated
privileges:

- Rewrite getuid(2) to return DEFAULT_UID by default and 0 if the
  process has elevated privileges.
- geteuid(2) and the corresponding functions for groups are aliases
  for getuid(2).
- Change root's home directory to be whatever GetSystemDirectory()
  returns, probably C:/Windows/System32 in most cases.
- Remove the special handling of geteuid(2) in the line editing code.

With these changes the shell started by 'su' is a lot more like a
*nix root shell.

5 files changed, 42 insertions, 32 deletions

diff --git a/include/mingw.h b/include/mingw.h
index ead07ae82..7aa2d5cc9 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -9,7 +9,7 @@ typedef int gid_t;
 typedef int uid_t;
 
 #define DEFAULT_UID 4095
-#define DEFAULT_GID 4095
+#define DEFAULT_GID DEFAULT_UID
 
 /*
  * arpa/inet.h
@@ -388,13 +388,13 @@ char *mingw_getcwd(char *pointer, int len);
 off_t mingw_lseek(int fd, off_t offset, int whence);
 
 
-IMPL(getgid,int,DEFAULT_GID,void);
+int getuid(void);
+#define getgid getuid
+#define geteuid getuid
+#define getegid getuid
 int getgroups(int n, gid_t *groups);
 IMPL(getppid,int,1,void);
-IMPL(getegid,int,DEFAULT_GID,void);
-IMPL(geteuid,int,DEFAULT_UID,void);
 NOIMPL(getsid,pid_t pid UNUSED_PARAM);
-IMPL(getuid,int,DEFAULT_UID,void);
 int getlogin_r(char *buf, size_t len);
 int fcntl(int fd, int cmd, ...);
 int fsync(int fd);
@@ -521,4 +521,3 @@ ULONGLONG CompatGetTickCount64(void);
 ssize_t get_random_bytes(void *buf, ssize_t count);
 int enumerate_links(const char *file, char *name);
 void hide_console(void);
-int is_admin(void);
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 9e24d410d..95f92aa75 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -45,9 +45,6 @@
 # define _POSIX_VDISABLE '\0'
 #endif
 
-#if ENABLE_PLATFORM_MINGW32
-# define geteuid() (is_admin() ? 0 : DEFAULT_UID)
-#endif
 
 #ifdef TEST
 # define ENABLE_FEATURE_EDITING 0
diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index 787bcbbef..6396a7b88 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -47,10 +47,12 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         /* info.hwnd = NULL; */
         info.lpVerb = "runas";
         info.lpFile = bb_path;
-        /* ShellExecuteEx() always runs system binaries in C:\Windows\System32.
-         * Pass the directory we want to the shell. */
+        /* It seems that when ShellExecuteEx() runs binaries residing in
+         * certain 'system' directories it sets the current directory of
+         * the process to %SYSTEMROOT%\System32.  Override this by passing
+         * the directory we want to the shell. */
         info.lpParameters =
-                xasprintf("--busybox ash -d \"%s\" -t \"BusyBox ash (su)\" ",
+                xasprintf("--busybox ash -d \"%s\" -t \"BusyBox ash (Admin)\" ",
                                         getcwd(NULL, 0));
         if (opt_command)
                 info.lpParameters =
diff --git a/shell/ash.c b/shell/ash.c
index 6b70dcde3..10da3ebed 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -15014,9 +15014,11 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
  state2:
         state = 3;
         if (
+#if ENABLE_PLATFORM_POSIX
 #ifndef linux
          getuid() == geteuid() && getgid() == getegid() &&
 #endif
+#endif
          iflag
         ) {
                 const char *shinit = lookupvar("ENV");
diff --git a/win32/mingw.c b/win32/mingw.c
index b50c1ecee..84b059506 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -872,6 +872,25 @@ static char *get_user_name(void)
         return user_name;
 }
 
+int getuid(void)
+{
+        int ret = DEFAULT_UID;
+        HANDLE h;
+
+        if (OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &h)) {
+                TOKEN_ELEVATION elevation;
+                DWORD size = sizeof(TOKEN_ELEVATION);
+
+                if (GetTokenInformation(h, TokenElevation, &elevation,
+                                        sizeof(elevation), &size)) {
+                        if (elevation.TokenIsElevated)
+                                ret = 0;
+                }
+                CloseHandle(h);
+        }
+        return ret;
+}
+
 struct passwd *getpwnam(const char *name)
 {
         const char *myname;
@@ -892,8 +911,17 @@ struct passwd *getpwuid(uid_t uid)
         static struct passwd p;
 
         if (uid == 0) {
+                static char *buf = NULL;
+                char dir[PATH_MAX];
+
+                if (!buf) {
+                        buf = xzalloc(PATH_MAX);
+                        GetSystemDirectory(dir, PATH_MAX);
+                        realpath(dir, buf);
+                }
+
                 p.pw_name = (char *)"root";
-                p.pw_dir = (char *)"/";
+                p.pw_dir = buf;
         }
         else if (uid == DEFAULT_UID && (p.pw_name=get_user_name()) != NULL) {
                 p.pw_dir = gethomedir();
@@ -949,7 +977,7 @@ int getgroups(int n, gid_t *groups)
                 return 1;
         }
 
-        groups[0] = DEFAULT_GID;
+        groups[0] = getgid();
         return 1;
 }
 
@@ -1576,21 +1604,3 @@ void hide_console(void)
         }
 }
 #endif
-
-int is_admin(void)
-{
-        int ret = FALSE;
-        HANDLE h;
-
-        if (OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &h)) {
-                TOKEN_ELEVATION elevation;
-                DWORD size = sizeof(TOKEN_ELEVATION);
-
-                if (GetTokenInformation(h, TokenElevation, &elevation,
-                                        sizeof(elevation), &size)) {
-                        ret = elevation.TokenIsElevated;
-                }
-                CloseHandle(h);
-        }
-        return ret;
-}