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att
GitHub Repository: att/ast
 Path: blob/master/src/lib/libast/path/pathshell.c
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/***********************************************************************

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*                                                                      *

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*               This software is part of the ast package               *

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*          Copyright (c) 1985-2011 AT&T Intellectual Property          *

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*                      and is licensed under the                       *

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*                 Eclipse Public License, Version 1.0                  *

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*                    by AT&T Intellectual Property                     *

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*                                                                      *

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*                A copy of the License is available at                 *

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*          http://www.eclipse.org/org/documents/epl-v10.html           *

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*         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *

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*                                                                      *

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*              Information and Software Systems Research               *

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*                            AT&T Research                             *

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*                           Florham Park NJ                            *

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*                                                                      *

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*                 Glenn Fowler <[email protected]>                  *

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*                  David Korn <[email protected]>                   *

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*                   Phong Vo <[email protected]>                    *

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*                                                                      *

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***********************************************************************/

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#pragma prototyped

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/*

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 * G. S. Fowler

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 * D. G. Korn

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 * AT&T Bell Laboratories

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 *

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 * shell library support

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 */

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#include <ast.h>

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#include <sys/stat.h>

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/*

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 * return pointer to the full path name of the shell

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 *

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 * SHELL is read from the environment and must start with /

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 *

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 * if set-uid or set-gid then the executable and its containing

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 * directory must not be owned by the real user/group

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 *

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 * root/administrator has its own test

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 *

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 * astconf("SH",NiL,NiL) is returned by default

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 *

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 * NOTE: csh is rejected because the bsh/csh differentiation is

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 *       not done for `csh script arg ...'

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 */

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char*

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pathshell(void)

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{

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	register char*	sh;

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	int		ru;

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	int		eu;

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	int		rg;

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	int		eg;

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	struct stat	st;

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	static char*	val;

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	if ((sh = getenv("SHELL")) && *sh == '/' && strmatch(sh, "*/(sh|*[!cC]sh)*([[:digit:]])?(-+([.[:alnum:]]))?(.exe)"))

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	{

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		if (!(ru = getuid()) || !eaccess("/bin", W_OK))

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		{

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			if (stat(sh, &st))

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				goto defshell;

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			if (ru != st.st_uid && !strmatch(sh, "?(/usr)?(/local)/?([ls])bin/?([[:lower:]])sh?(.exe)"))

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				goto defshell;

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		}

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		else

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		{

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			eu = geteuid();

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			rg = getgid();

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			eg = getegid();

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			if (ru != eu || rg != eg)

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			{

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				char*	s;

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				char	dir[PATH_MAX];

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				s = sh;

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				for (;;)

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				{

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					if (stat(s, &st))

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						goto defshell;

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					if (ru != eu && st.st_uid == ru)

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						goto defshell;

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					if (rg != eg && st.st_gid == rg)

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						goto defshell;

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					if (s != sh)

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						break;

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					if (strlen(s) >= sizeof(dir))

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						goto defshell;

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					strcpy(dir, s);

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					if (!(s = strrchr(dir, '/')))

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						break;

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					*s = 0;

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					s = dir;

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				}

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			}

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		}

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		return sh;

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	}

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 defshell:

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	if (!(sh = val))

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	{

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		if (!*(sh = astconf("SH", NiL, NiL)) || *sh != '/' || eaccess(sh, X_OK) || !(sh = strdup(sh)))

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			sh = "/bin/sh";

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		val = sh;

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	}

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	return sh;

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}

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