hush/applets/applets.c

/* vi: set sw=4 ts=4: */
/*
 * Utility routines.
 *
 * Copyright (C) tons of folks.  Tracking down who wrote what
 * isn't something I'm going to worry about...  If you wrote something
 * here, please feel free to acknowledge your work.
 *
 * Based in part on code from sash, Copyright (c) 1999 by David I. Bell
 * Permission has been granted to redistribute this code under the GPL.
 *
 * Licensed under GPLv2 or later, see file License in this tarball for details.
 */

#include <assert.h>
#include "busybox.h"

#define PROTOTYPES
#include "applets.h"
#undef PROTOTYPES


/* Apparently uclibc defines __GLIBC__ (compat trick?). Oh well. */
#if ENABLE_STATIC && defined(__GLIBC__) && !defined(__UCLIBC__)
#warning Static linking against glibc produces buggy executables
#warning (glibc does not cope well with ld --gc-sections).
#warning See sources.redhat.com/bugzilla/show_bug.cgi?id=3400
#warning Note that glibc is unsuitable for static linking anyway.
#warning If you still want to do it, remove -Wl,--gc-sections
#warning from top-level Makefile and remove this warning.
#endif

#if ENABLE_SHOW_USAGE && !ENABLE_FEATURE_COMPRESS_USAGE
static const char usage_messages[] =
#define MAKE_USAGE
#include "usage.h"
#include "applets.h"
;
#undef MAKE_USAGE
#else
#define usage_messages 0
#endif /* ENABLE_SHOW_USAGE */

#undef APPLET
#undef APPLET_NOUSAGE
#undef PROTOTYPES
#include "applets.h"

static struct BB_applet *applet_using;

/* The -1 arises because of the {0,NULL,0,-1} entry. */
const unsigned short NUM_APPLETS = (sizeof(applets) / sizeof(struct BB_applet) - 1);


#if ENABLE_FEATURE_SUID_CONFIG

#include <ctype.h>

/* applets [] is const, so we have to define this "override" structure */
static struct BB_suid_config
{
	struct BB_applet *m_applet;

	uid_t m_uid;
	gid_t m_gid;
	mode_t m_mode;

	struct BB_suid_config *m_next;
} *suid_config;

static int suid_cfg_readable;

/* check if u is member of group g */
static int ingroup(uid_t u, gid_t g)
{
	struct group *grp = getgrgid(g);

	if (grp) {
		char **mem;

		for (mem = grp->gr_mem; *mem; mem++) {
			struct passwd *pwd = getpwnam(*mem);

			if (pwd && (pwd->pw_uid == u))
				return 1;
		}
	}
	return 0;
}

/* This should probably be a libbb routine.  In that case,
 * I'd probably rename it to something like bb_trimmed_slice.
 */
static char *get_trimmed_slice(char *s, char *e)
{
	/* First, consider the value at e to be nul and back up until we
	 * reach a non-space char.  Set the char after that (possibly at
	 * the original e) to nul. */
	while (e-- > s) {
		if (!isspace(*e)) {
			break;
		}
	}
	e[1] = 0;

	/* Next, advance past all leading space and return a ptr to the
	 * first non-space char; possibly the terminating nul. */
	return skip_whitespace(s);
}


#define parse_error(x)  do { errmsg = x; goto pe_label; } while(0)

/* Don't depend on the tools to combine strings. */
static const char config_file[] = "/etc/busybox.conf";

/* There are 4 chars + 1 nul for each of user/group/other. */
static const char mode_chars[] = "Ssx-\0Ssx-\0Ttx-";

/* We don't supply a value for the nul, so an index adjustment is
 * necessary below.  Also, we use unsigned short here to save some
 * space even though these are really mode_t values. */
static const unsigned short mode_mask[] = {
	/*  SST         sst                 xxx   --- */
	S_ISUID,    S_ISUID|S_IXUSR,    S_IXUSR,    0,	/* user */
	S_ISGID,    S_ISGID|S_IXGRP,    S_IXGRP,    0,	/* group */
	0,          S_IXOTH,            S_IXOTH,    0	/* other */
};

static void parse_config_file(void)
{
	struct BB_suid_config *sct_head;
	struct BB_suid_config *sct;
	struct BB_applet *applet;
	FILE *f;
	const char *errmsg;
	char *s;
	char *e;
	int i, lc, section;
	char buffer[256];
	struct stat st;

	assert(!suid_config); /* Should be set to NULL by bss init. */

	if ((stat(config_file, &st) != 0)       /* No config file? */
	 || !S_ISREG(st.st_mode)                /* Not a regular file? */
	 || (st.st_uid != 0)                    /* Not owned by root? */
	 || (st.st_mode & (S_IWGRP | S_IWOTH))  /* Writable by non-root? */
	 || !(f = fopen(config_file, "r"))      /* Cannot open? */
	) {
		return;
	}

	suid_cfg_readable = 1;
	sct_head = NULL;
	section = lc = 0;

	do {
		s = buffer;

		if (!fgets(s, sizeof(buffer), f)) { /* Are we done? */
			if (ferror(f)) {   /* Make sure it wasn't a read error. */
				parse_error("reading");
			}
			fclose(f);
			suid_config = sct_head;	/* Success, so set the pointer. */
			return;
		}

		lc++;					/* Got a (partial) line. */

		/* If a line is too long for our buffer, we consider it an error.
		 * The following test does mistreat one corner case though.
		 * If the final line of the file does not end with a newline and
		 * yet exactly fills the buffer, it will be treated as too long
		 * even though there isn't really a problem.  But it isn't really
		 * worth adding code to deal with such an unlikely situation, and
		 * we do err on the side of caution.  Besides, the line would be
		 * too long if it did end with a newline. */
		if (!strchr(s, '\n') && !feof(f)) {
			parse_error("line too long");
		}

		/* Trim leading and trailing whitespace, ignoring comments, and
		 * check if the resulting string is empty. */
		s = get_trimmed_slice(s, strchrnul(s, '#'));
		if (!*s) {
			continue;
		}

		/* Check for a section header. */

		if (*s == '[') {
			/* Unlike the old code, we ignore leading and trailing
			 * whitespace for the section name.  We also require that
			 * there are no stray characters after the closing bracket. */
			e = strchr(s, ']');
			if (!e   /* Missing right bracket? */
			 || e[1] /* Trailing characters? */
			 || !*(s = get_trimmed_slice(s+1, e)) /* Missing name? */
			) {
				parse_error("section header");
			}
			/* Right now we only have one section so just check it.
			 * If more sections are added in the future, please don't
			 * resort to cascading ifs with multiple strcasecmp calls.
			 * That kind of bloated code is all too common.  A loop
			 * and a string table would be a better choice unless the
			 * number of sections is very small. */
			if (strcasecmp(s, "SUID") == 0) {
				section = 1;
				continue;
			}
			section = -1;	/* Unknown section so set to skip. */
			continue;
		}

		/* Process sections. */

		if (section == 1) {		/* SUID */
			/* Since we trimmed leading and trailing space above, we're
			 * now looking for strings of the form
			 *    <key>[::space::]*=[::space::]*<value>
			 * where both key and value could contain inner whitespace. */

			/* First get the key (an applet name in our case). */
			e = strchr(s, '=');
			if (e) {
				s = get_trimmed_slice(s, e);
			}
			if (!e || !*s) {	/* Missing '=' or empty key. */
				parse_error("keyword");
			}

			/* Ok, we have an applet name.  Process the rhs if this
			 * applet is currently built in and ignore it otherwise.
			 * Note: This can hide config file bugs which only pop
			 * up when the busybox configuration is changed. */
			applet = find_applet_by_name(s);
			if (applet) {
				/* Note: We currently don't check for duplicates!
				 * The last config line for each applet will be the
				 * one used since we insert at the head of the list.
				 * I suppose this could be considered a feature. */
				sct = xmalloc(sizeof(struct BB_suid_config));
				sct->m_applet = applet;
				sct->m_mode = 0;
				sct->m_next = sct_head;
				sct_head = sct;

				/* Get the specified mode. */

				e = skip_whitespace(e+1);

				for (i = 0; i < 3; i++) {
					const char *q;
					q = strchrnul(mode_chars + 5*i, *e++);
					if (!*q) {
						parse_error("mode");
					}
					/* Adjust by -i to account for nul. */
					sct->m_mode |= mode_mask[(q - mode_chars) - i];
				}

				/* Now get the the user/group info. */

				s = skip_whitespace(e);

				/* Note: We require whitespace between the mode and the
				 * user/group info. */
				if ((s == e) || !(e = strchr(s, '.'))) {
					parse_error("<uid>.<gid>");
				}
				*e++ = '\0';

				/* We can't use get_ug_id here since it would exit()
				 * if a uid or gid was not found.  Oh well... */
				sct->m_uid = bb_strtoul(s, NULL, 10);
				if (errno) {
					struct passwd *pwd = getpwnam(s);
					if (!pwd) {
						parse_error("user");
					}
					sct->m_uid = pwd->pw_uid;
				}

				sct->m_gid = bb_strtoul(e, NULL, 10);
				if (errno) {
					struct group *grp;
					grp = getgrnam(e);
					if (!grp) {
						parse_error("group");
					}
					sct->m_gid = grp->gr_gid;
				}
			}
			continue;
		}

		/* Unknown sections are ignored. */

		/* Encountering configuration lines prior to seeing a
		 * section header is treated as an error.  This is how
		 * the old code worked, but it may not be desirable.
		 * We may want to simply ignore such lines in case they
		 * are used in some future version of busybox. */
		if (!section) {
			parse_error("keyword outside section");
		}

	} while (1);

 pe_label:
	fprintf(stderr, "Parse error in %s, line %d: %s\n",
			config_file, lc, errmsg);

	fclose(f);
	/* Release any allocated memory before returning. */
	while (sct_head) {
		sct = sct_head->m_next;
		free(sct_head);
		sct_head = sct;
	}
}

#else
#define parse_config_file() ((void)0)
#endif /* CONFIG_FEATURE_SUID_CONFIG */

#if ENABLE_FEATURE_SUID
static void check_suid(struct BB_applet *applet)
{
	uid_t ruid = getuid();               /* real [ug]id */
	uid_t rgid = getgid();

#if ENABLE_FEATURE_SUID_CONFIG
	if (suid_cfg_readable) {
		struct BB_suid_config *sct;
		mode_t m;

		for (sct = suid_config; sct; sct = sct->m_next) {
			if (sct->m_applet == applet)
				goto found;
		}
		/* default: drop all privileges */
		xsetgid(rgid);
		xsetuid(ruid);
		return;
 found:
		m = sct->m_mode;
		if (sct->m_uid == ruid)
			/* same uid */
			m >>= 6;
		else if ((sct->m_gid == rgid) || ingroup(ruid, sct->m_gid))
			/* same group / in group */
			m >>= 3;

		if (!(m & S_IXOTH))           /* is x bit not set ? */
			bb_error_msg_and_die("you have no permission to run this applet!");

		if (sct->m_gid != 0) {
			/* _both_ have to be set for sgid */
			if ((sct->m_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
				xsetgid(sct->m_gid);
			} else xsetgid(rgid); /* no sgid -> drop */
		}
		if (sct->m_uid != 0) {
			if (sct->m_mode & S_ISUID) xsetuid(sct->m_uid);
			else xsetuid(ruid); /* no suid -> drop */
		}
		return;
	}
#if !ENABLE_FEATURE_SUID_CONFIG_QUIET
	{
		static smallint onetime = 0;

		if (!onetime) {
			onetime = 1;
			fprintf(stderr, "Using fallback suid method\n");
		}
	}
#endif
#endif

	if (applet->need_suid == _BB_SUID_ALWAYS) {
		if (geteuid())
			bb_error_msg_and_die("applet requires root privileges!");
	} else if (applet->need_suid == _BB_SUID_NEVER) {
		xsetgid(rgid);                          /* drop all privileges */
		xsetuid(ruid);
	}
}
#else
#define check_suid(x)
#endif /* CONFIG_FEATURE_SUID */



#if ENABLE_FEATURE_COMPRESS_USAGE

#include "usage_compressed.h"
#include "unarchive.h"

static const char *unpack_usage_messages(void)
{
	int input[2], output[2], pid;
	char *buf;

	if (pipe(input) < 0 || pipe(output) < 0)
		exit(1);

	pid = fork();
	switch (pid) {
	case -1: /* error */
		exit(1);
	case 0: /* child */
		close(input[1]);
		close(output[0]);
		uncompressStream(input[0], output[1]);
		exit(0);
	}
	/* parent */

	close(input[0]);
	close(output[1]);
	pid = fork();
	switch (pid) {
	case -1: /* error */
		exit(1);
	case 0: /* child */
		full_write(input[1], packed_usage, sizeof(packed_usage));
		exit(0);
	}
	/* parent */
	close(input[1]);

	buf = xmalloc(SIZEOF_usage_messages);
	full_read(output[0], buf, SIZEOF_usage_messages);
	return buf;
}

#else
#define unpack_usage_messages() usage_messages
#endif /* ENABLE_FEATURE_COMPRESS_USAGE */

void bb_show_usage(void)
{
	if (ENABLE_SHOW_USAGE) {
		const char *format_string;
		const char *usage_string = unpack_usage_messages();
		int i;

		for (i = applet_using - applets; i > 0;)
			if (!*usage_string++) --i;

		format_string = "%s\n\nUsage: %s %s\n\n";
		if (*usage_string == '\b')
			format_string = "%s\n\nNo help available.\n\n";
		fprintf(stderr, format_string, bb_msg_full_version,
			applet_using->name, usage_string);
	}

	exit(xfunc_error_retval);
}

static int applet_name_compare(const void *name, const void *vapplet)
{
	const struct BB_applet *applet = vapplet;

	return strcmp(name, applet->name);
}

struct BB_applet *find_applet_by_name(const char *name)
{
	return bsearch(name, applets, NUM_APPLETS, sizeof(struct BB_applet),
				applet_name_compare);
}

void run_applet_by_name(const char *name, int argc, char **argv)
{
	if (ENABLE_FEATURE_SUID_CONFIG)
		parse_config_file();

	/* Do a binary search to find the applet entry given the name. */
	applet_using = find_applet_by_name(name);
	if (applet_using) {
		applet_name = applet_using->name;
		if (argc == 2 && !strcmp(argv[1], "--help"))
			bb_show_usage();
		if (ENABLE_FEATURE_SUID)
			check_suid(applet_using);
		exit(applet_using->main(argc, argv));
	}
	if (!strncmp(name, "busybox", 7))
		exit(busybox_main(argc, argv));
}