su: handle restricted disk drivers

Certain tools which allow disk image files and RAM disks to be
mounted were found to lack a feature used to implement realpath(3).
This resulted in a segfault in the 'su' applet when it was run in
such a virtual filesystem.

'su' uses realpath(3) to canonicalise the current directory.  This
is only really required to handle network shares mapped to a drive
letter.  (GitHub issue #148)

- If the call to realpath(3) fails for some reason fall back to
  using the current directory determined by calling getcwd(3).

- If getcwd(3) fails simply don't pass any directory to the shell
  being started by 'su'.

Also, ensure all allocated memory is freed, if required.

(GitHub issue #389)

Adds 16-32 bytes.

1 files changed, 18 insertions, 6 deletions

diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index 240a692bc..89ccec220 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -40,7 +40,7 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         unsigned opt;
         char *opt_command = NULL;
         SHELLEXECUTEINFO info;
-        char *bb_path, *cwd, *q, *args;
+        char *bb_path, *cwd, *realcwd, *q, *args;
         DECLARE_PROC_ADDR(BOOL, ShellExecuteExA, SHELLEXECUTEINFOA *);
 
         opt = getopt32(argv, "c:NW", &opt_command);
@@ -74,11 +74,16 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
          * a network share it may not be available once we have elevated
          * privileges.
          */
-        cwd = xmalloc_realpath(getcwd(NULL, 0));
-        q = quote_arg(cwd);
-        args = xasprintf("--busybox ash -d %s -t \"BusyBox ash (Admin)\"", q);
-        free(q);
-        free(cwd);
+        args = xasprintf("--busybox ash -t \"BusyBox ash (Admin)\"");
+
+        cwd = getcwd(NULL, 0);
+        realcwd = cwd ? xmalloc_realpath(cwd) : NULL;
+        if (realcwd || cwd) {
+                args = xappendword(args, "-d");
+                q = quote_arg(realcwd ?: cwd);
+                args = xappendword(args, q);
+                free(q);
+        }
 
         if (opt & OPT_N)
                 args = xappendword(args, "-N");
@@ -106,6 +111,13 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         if (!ShellExecuteExA(&info))
                 return 1;
 
+        if (ENABLE_FEATURE_CLEAN_UP) {
+                free(bb_path);
+                free(cwd);
+                free(realcwd);
+                free(args);
+        }
+
         if (opt & OPT_W) {
                 DWORD r;