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*
pathshell(void)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 }
113