[Toybox] [patch] add su

[Strake]

On 14/08/2013, Rob Landley <rob at landley.net> wrote:
> The root user is uid 0, which could be _named_ anything. (Crazy people
> say "wheel".) So we need a getwpuid(0) else getpwnam(name) and then do
> the shadow lookup based on that name.

I would likely write a function getspuid, but I'm not sure how you
wish to do this, so I'll leave it for now.

>> +  passhash = crypt (toybuf, shp -> sp_pwdp);
>> +  if (!passhash) perror_exit ("failed to compute password hash");
>> +  for (ii = 0; toybuf[ii]; ii++) toybuf[ii] = 0;
>
> Proper paranoia would probably swap those last two lines.

Derp.

> Hmmm, should the suid plumbing in main.c mlockall() when we don't drop
> privs?

I think so. Particularly if someone can read the swap medium but not /dev/mem.

>> +  if (toys.optflags & FLAG_c) {
>> +    argv[1] = toys.optflags & FLAG_l ? "-lc" : "-c";
>> +    argv[2] = TT.cArgu;
>> +    argv += 2;
>> +  }
>> +  else if (toys.optflags & FLAG_l) (argv++)[1] = "-l";
>
> Is there a reason you can't do -l -c as two arguments and just test
> once?

No, was just stupid.


>From 29dc3c3206c7280d159c9d0e27125fdbe1dd0a61 Mon Sep 17 00:00:00 2001
From: Strake <strake888 at gmail.com>
Date: Mon, 30 Jun 2003 15:50:05 -0500
Subject: [PATCH] su: cleanery

* make help message more like others
* s/TT\.(.)Argu/TT.\1/g
* move environ to toys.h
* simplify failure messages
* clear password before quit
* not check what execve returns
* -lc
---
 toys.h            |  2 ++
 toys/pending/su.c | 67 +++++++++++++++++++++++++++----------------------------
 2 files changed, 35 insertions(+), 34 deletions(-)

diff --git a/toys.h b/toys.h
index 2ce1d0a..c810123 100644
--- a/toys.h
+++ b/toys.h
@@ -117,6 +117,8 @@ extern struct toy_context {

 extern char toybuf[4096];

+extern char **environ;
+
 #define GLOBALS(...)

 #define ARRAY_LEN(array) (sizeof(array)/sizeof(*array))
diff --git a/toys/pending/su.c b/toys/pending/su.c
index cf9b599..529042b 100644
--- a/toys/pending/su.c
+++ b/toys/pending/su.c
@@ -10,14 +10,14 @@ config SU
   bool "su"
   default n
   help
-    usage: su [-lmp] [-c cmd] [-s shell] [user [argu...]]
-
+    usage: su [-lmp] [-c CMD] [-s SHELL] [USER [ARGS...]]
+
     Switch to given user, or root if not given, and call a shell with
the given arguments.
-
+
     options:
       -s  shell to call
       -c  command to pass to shell with -c
-
+
     flags:
       -l      login shell
       -(m|p)  preserve environment
@@ -27,12 +27,10 @@ config SU
 #include "toys.h"

 GLOBALS(
-  char *sArgu;
-  char *cArgu;
+  char *s;
+  char *c;
 )

-extern char **environ;
-
 static void deny () {
   printf ("Denied\n");
   xexit ();
@@ -43,56 +41,57 @@ void su_main () {
   struct passwd *up;
   struct spwd *shp;
   long ii;
-
+
   if (toys.optc && strcmp ("-", toys.optargs[0]) == 0) {
     toys.optflags |= FLAG_l;
     toys.optc--; toys.optargs++;
   }
-
+
   if (toys.optc) {
     name = toys.optargs[0];
     toys.optc--; toys.optargs++;
   }
   else name = "root";
   shp = getspnam (name);
-  if (!shp) perror_exit ("failed to find password");
-
+  if (!shp) perror_exit ("can't find password");
+
   switch (shp -> sp_pwdp[0]) {
   case '!': deny ();
   case '$': break;
   default : error_exit ("bad password format");
   }

-  if (read_password (toybuf, sizeof (toybuf), "Password: ") != 0)
perror_exit ("failed to read password");
+  if (read_password (toybuf, sizeof (toybuf), "Password: ") != 0)
perror_exit ("can't read password");

   passhash = crypt (toybuf, shp -> sp_pwdp);
-  if (!passhash) perror_exit ("failed to compute password hash");
   for (ii = 0; toybuf[ii]; ii++) toybuf[ii] = 0;
-
+  if (!passhash) perror_exit ("can't crypt");
+
   if (strcmp (passhash, shp -> sp_pwdp) != 0) deny ();
-
+
   up = getpwnam (name);
-  if (!up) perror_exit ("failed to getpwnam");
-
-  if (setuid (up -> pw_uid) < 0) perror_exit ("failed to setuid");
-  if (chdir  (up -> pw_dir) < 0) perror_exit ("failed to chdir");
-
+  if (!up) perror_exit ("can't getpwnam");
+
+  xsetuid (up -> pw_uid);
+  xchdir  (up -> pw_dir);
+
   argu = xmalloc (sizeof (char *)*(toys.optc + 4));
   argv = argu;
-  argv[0] = toys.optflags & FLAG_s ? TT.sArgu : up -> pw_shell;
+  argv[0] = toys.optflags & FLAG_s ? TT.s : up -> pw_shell;
+  if (toys.optflags & FLAG_l) (argv++)[1] = "-l";
   if (toys.optflags & FLAG_c) {
-    argv[1] = toys.optflags & FLAG_l ? "-lc" : "-c";
-    argv[2] = TT.cArgu;
+    argv[1] = "-c";
+    argv[2] = TT.c;
     argv += 2;
   }
-  else if (toys.optflags & FLAG_l) (argv++)[1] = "-l";
-  for (ii = 0; ii < toys.optc; ii++) argv[ii + 1] = toys.optargs[ii];
-  if (execve (argu[0], argu,
-              toys.optflags & FLAG_l ? (char *[]){
-                xmsprintf ( "HOME=%s", up -> pw_dir),
-                xmsprintf ("SHELL=%s", up -> pw_shell),
-                xmsprintf ( "USER=%s", up -> pw_name),
-                xmsprintf ( "TERM=%s", getenv ("TERM")),
-                0
-              } : environ) < 0) perror_exit ("failed to exec %s", argu[0]);
+  memcpy (argv + 1, toys.optargs, sizeof (char *)*toys.optc);
+  execve (argu[0], argu,
+          toys.optflags & FLAG_l ? (char *[]){
+            xmsprintf ( "HOME=%s", up -> pw_dir),
+            xmsprintf ("SHELL=%s", up -> pw_shell),
+            xmsprintf ( "USER=%s", up -> pw_name),
+            xmsprintf ( "TERM=%s", getenv ("TERM")),
+            0
+          } : environ);
+  perror_exit ("can't exec %s", argu[0]);
 }
-- 
1.8.3.4