texlive/nobody.c

/*
 * Nobody	For user root run a specific program as user nobody
 *
 * Usage:	nobody [texhash|ls|find|false|true]
 *
 *		Copyright (C) 2010,2012 Werner Fink
 *
 *		This program is free software; you can redistribute it and/or modify
 *		it under the terms of the GNU General Public License as published by
 *		the Free Software Foundation; either version 2 of the License, or
 *		(at your option) any later version.
 *
 *		This program is distributed in the hope that it will be useful,
 *		but WITHOUT ANY WARRANTY; without even the implied warranty of
 *		MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *		GNU General Public License for more details.
 *
 *		You should have received a copy of the GNU General Public License
 *		along with this program; if not, write to the Free Software
 *		Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 */

#include <errno.h>
#include <limits.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>

extern char **environ;

/*
 * This list is used to authenticate the program running.
 * It is fixed at compile time to avoid a full class of 
 * dangers ...
 */
static struct {
    const char *prog;
    const char *run;
} *lp, list[] =
{   /* prog		run			*/
    { "mktexlsr",	"/usr/bin/mktexlsr"	},
    { "texhash",	"/usr/bin/mktexlsr"	},
    { "ls",		"/bin/ls"		},
    { "true",		"/bin/true"		},
    { "false",		"/bin/false"		},
    { "find",		"/usr/bin/find"		},
#ifdef DEBUG
    { "id",		"/usr/bin/id"		},
    { "printenv",	"/usr/bin/printenv"	},
#endif
    { 0,		0,			}};

static struct {
    const char *name;
    const char *value;
} *ep, envp[] =
{   { "TERM",		0			},
    { "PATH",		"/bin:/usr/bin"		},
    { "POSIXLY_CORRECT",0			},
    { "NLSPATH",	0			},
    { "LANG",		0			},
    { "LC_ALL",		0			},
    { "LC_CTYPE",	0			},
    { "LC_COLLATE",	0			},
    { "LC_MESSAGES",	0			},
    { "COLUMNS",	0			},
    { "TABSIZE",	0			},
    { "TIME_STYLE",	0			},
    { "LS_COLORS",	0			},
    { "LS_BLOCK_SIZE",	0			},
    { "BLOCK_SIZE",	0			},
    { "BLOCKSIZE",	0			},
    { 0,		0			}};

int main(int argc, char *argv[])
{
    char *program_name;
    struct passwd *pwd;
    uid_t ruid = getuid();
    uid_t euid = geteuid();
    gid_t rgid = getgid();

    if (argc > 1)
	program_name = argv[1];
    else
	program_name = "true";
    argv++;
    argc--;

    if (*program_name == '/') {
	for (lp = list; lp->run  && strcmp(program_name, lp->run ); lp++) ;
    } else {
	for (lp = list; lp->prog && strcmp(program_name, lp->prog); lp++) ;
    }

    if (!lp->prog) {
	errno = EBADRQC;
	fprintf(stderr, "nobody: Usage:\n");
	fprintf(stderr, "   nobody [");
	for (lp = list; lp->prog; lp++)
	    fprintf(stderr, "%s%c", lp->prog, (lp+1)->prog ? '|' : '\0');
	fprintf(stderr, "]\n");
	goto err;
    }

    if ((pwd = getpwnam("nobody")) == (struct passwd*)0)
	goto err;

    if (ruid != pwd->pw_uid || euid != pwd->pw_gid) {
	int initgrp = 0;

	if (ruid != pwd->pw_uid) {
	    initgrp = 1;
	    ruid = pwd->pw_uid;
	    rgid = pwd->pw_gid;
	} else {
	    pwd->pw_uid = ruid;
	    pwd->pw_gid = rgid;
	}

	if (setregid(rgid, pwd->pw_gid))
	    goto err;
	if (initgrp && initgroups(pwd->pw_name, rgid))
	    goto err;
	if (setreuid(ruid, pwd->pw_uid))
	    goto err;

	if (initgrp) {

	    for (ep = envp; ep->name; ep++) {
		if (ep->value)
		    continue;
		ep->value = getenv(ep->name);
	    }

	    clearenv();

	    if (setenv("HOME", pwd->pw_dir, 1) < 0)
		goto err;
	    if (setenv("USER", pwd->pw_name, 1) < 0)
		goto err;
	    if (setenv("LOGNAME", pwd->pw_name, 1) < 0)
		goto err;
	    if (setenv("GROUP", pwd->pw_name, 1) < 0)
		goto err;
	    if (setenv("SHELL", pwd->pw_shell, 1) < 0)
		goto err;

	    for (ep = envp; ep->name; ep++) {
		if (!ep->value)
		    continue;
		setenv(ep->name, ep->value, 1);
	    }

	    if (strcmp(lp->prog, "find") == 0) {
		int n;
		for (n = 0; n < argc; n++) {
		    if (!argv[n] || *argv[n] == '\0')
			continue;
		    if (strncmp(argv[n], "-exec", 5) == 0) {
			errno = ENOTSUP;
			goto err;
		    }
		    if (strncmp(argv[n], "-ok", 3) == 0) {
			errno = ENOTSUP;
			goto err;
		    }
		}
	    }
	    if (strcmp(lp->prog, "texhash") == 0 || strcmp(lp->prog, "mktexlsr") == 0) {
		int n;
		char buf[PATH_MAX+1], *lsr, *base;
		for (n = 1; n < argc; n++) {
		    if (!argv[n] || *argv[n] == '\0')
			continue;
		    if ((lsr = realpath(argv[n], buf)) == NULL)
			goto err;
		    if ((base = strrchr(lsr, '/')) == NULL) {
			errno = ENOTSUP;
			goto err;
		    }
		    if (strcmp(base, "/ls-R") != 0) {
			errno = ENOTSUP;
			goto err;
		    }
		    if (access(lsr, W_OK) != 0)
			goto err;
		}
	    }
	}
    }

    execve(lp->run, argv, environ);
err:
    fprintf(stderr, "nobody: ");
    perror(program_name);
    return 1;
}