usr/src/lib/libast/common/path/pathshell.c

   1 /***********************************************************************
   2 *                                                                      *
   3 *               This software is part of the ast package               *
   4 *          Copyright (c) 1985-2010 AT&T Intellectual Property          *
   5 *                      and is licensed under the                       *
   6 *                  Common Public License, Version 1.0                  *
   7 *                    by AT&T Intellectual Property                     *
   8 *                                                                      *
   9 *                A copy of the License is available at                 *
  10 *            http://www.opensource.org/licenses/cpl1.0.txt             *
  11 *         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
  12 *                                                                      *
  13 *              Information and Software Systems Research               *
  14 *                            AT&T Research                             *
  15 *                           Florham Park NJ                            *
  16 *                                                                      *
  17 *                 Glenn Fowler <gsf@research.att.com>                  *
  18 *                  David Korn <dgk@research.att.com>                   *
  19 *                   Phong Vo <kpv@research.att.com>                    *
  20 *                                                                      *
  21 ***********************************************************************/
  22 #pragma prototyped
  23 /*
  24  * G. S. Fowler
  25  * D. G. Korn
  26  * AT&T Bell Laboratories
  27  *
  28  * shell library support
  29  */
  30
  31 #include <ast.h>
  32 #include <sys/stat.h>
  33
  34 /*
  35  * return pointer to the full path name of the shell
  36  *
  37  * SHELL is read from the environment and must start with /
  38  *
  39  * if set-uid or set-gid then the executable and its containing
  40  * directory must not be owned by the real user/group
  41  *
  42  * root/administrator has its own test
  43  *
  44  * astconf("SH",NiL,NiL) is returned by default
  45  *
  46  * NOTE: csh is rejected because the bsh/csh differentiation is
  47  *       not done for `csh script arg ...'
  48  */
  49
  50 char*
  51 pathshell(void)
  52 {
  53         register char*  sh;
  54         int             ru;
  55         int             eu;
  56         int             rg;
  57         int             eg;
  58         struct stat     st;
  59
  60         static char*    val;
  61
  62         if ((sh = getenv("SHELL")) && *sh == '/' && strmatch(sh, "*/(sh|*[!cC]sh)*([[:digit:]])?(-+([.[:alnum:]]))?(.exe)"))
  63         {
  64                 if (!(ru = getuid()) || !eaccess("/bin", W_OK))
  65                 {
  66                         if (stat(sh, &st))
  67                                 goto defshell;
  68                         if (ru != st.st_uid && !strmatch(sh, "?(/usr)?(/local)/?([ls])bin/?([[:lower:]])sh?(.exe)"))
  69                                 goto defshell;
  70                 }
  71                 else
  72                 {
  73                         eu = geteuid();
  74                         rg = getgid();
  75                         eg = getegid();
  76                         if (ru != eu || rg != eg)
  77                         {
  78                                 char*   s;
  79                                 char    dir[PATH_MAX];
  80
  81                                 s = sh;
  82                                 for (;;)
  83                                 {
  84                                         if (stat(s, &st))
  85                                                 goto defshell;
  86                                         if (ru != eu && st.st_uid == ru)
  87                                                 goto defshell;
  88                                         if (rg != eg && st.st_gid == rg)
  89                                                 goto defshell;
  90                                         if (s != sh)
  91                                                 break;
  92                                         if (strlen(s) >= sizeof(dir))
  93                                                 goto defshell;
  94                                         strcpy(dir, s);
  95                                         if (!(s = strrchr(dir, '/')))
  96                                                 break;
  97                                         *s = 0;
  98                                         s = dir;
  99                                 }
 100                         }
 101                 }
 102                 return sh;
 103         }
 104  defshell:
 105         if (!(sh = val))
 106         {
 107                 if (!*(sh = astconf("SH", NiL, NiL)) || *sh != '/' || eaccess(sh, X_OK) || !(sh = strdup(sh)))
 108                         sh = "/bin/sh";
 109                 val = sh;
 110         }
 111         return sh;
 112 }