aboutsummaryrefslogtreecommitdiff
path: root/libbb/appletlib.c
blob: fa19e848889938a0d625b94d9a31a77168705e10 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
/* 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 GPL.
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
/* We are trying to not use printf, this benefits the case when selected
 * applets are really simple. Example:
 *
 * $ ./busybox
 * ...
 * Currently defined functions:
 *         basename, false, true
 *
 * $ size busybox
 *    text    data     bss     dec     hex filename
 *    4473      52      72    4597    11f5 busybox
 *
 * FEATURE_INSTALLER or FEATURE_SUID will still link printf routines in. :(
 */
#include "busybox.h"

#if !(defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) \
    || defined(__APPLE__) \
    )
# include <malloc.h> /* for mallopt */
#endif

/* Declare <applet>_main() */
#define PROTOTYPES
#include "applets.h"
#undef PROTOTYPES

/* Include generated applet names, pointers to <applet>_main, etc */
#include "applet_tables.h"
/* ...and if applet_tables generator says we have only one applet... */
#ifdef SINGLE_APPLET_MAIN
# undef ENABLE_FEATURE_INDIVIDUAL
# define ENABLE_FEATURE_INDIVIDUAL 1
# undef IF_FEATURE_INDIVIDUAL
# define IF_FEATURE_INDIVIDUAL(...) __VA_ARGS__
#endif

#include "usage_compressed.h"

#if ENABLE_FEATURE_SH_EMBEDDED_SCRIPTS
# define DEFINE_SCRIPT_DATA 1
# include "embedded_scripts.h"
#else
# define NUM_SCRIPTS 0
#endif
#if NUM_SCRIPTS > 0
# include "bb_archive.h"
static const char packed_scripts[] ALIGN1 = { PACKED_SCRIPTS };
#endif

/* "Do not compress usage text if uncompressed text is small
 *  and we don't include bunzip2 code for other reasons"
 *
 * Useful for mass one-applet rebuild (bunzip2 code is ~2.7k).
 *
 * Unlike BUNZIP2, if FEATURE_SEAMLESS_BZ2 is on, bunzip2 code is built but
 * still may be unused if none of the selected applets calls open_zipped()
 * or its friends; we test for (FEATURE_SEAMLESS_BZ2 && <APPLET>) instead.
 * For example, only if TAR and FEATURE_SEAMLESS_BZ2 are both selected,
 * then bunzip2 code will be linked in anyway, and disabling help compression
 * would be not optimal:
 */
#if UNPACKED_USAGE_LENGTH < 4*1024 \
 && !(ENABLE_FEATURE_SEAMLESS_BZ2 && ENABLE_TAR) \
 && !(ENABLE_FEATURE_SEAMLESS_BZ2 && ENABLE_MODPROBE) \
 && !(ENABLE_FEATURE_SEAMLESS_BZ2 && ENABLE_INSMOD) \
 && !(ENABLE_FEATURE_SEAMLESS_BZ2 && ENABLE_DEPMOD) \
 && !(ENABLE_FEATURE_SEAMLESS_BZ2 && ENABLE_MAN) \
 && !ENABLE_BUNZIP2 \
 && !ENABLE_BZCAT
# undef  ENABLE_FEATURE_COMPRESS_USAGE
# define ENABLE_FEATURE_COMPRESS_USAGE 0
#endif


unsigned FAST_FUNC string_array_len(char **argv)
{
	char **start = argv;

	while (*argv)
		argv++;

	return argv - start;
}


#if ENABLE_SHOW_USAGE && !ENABLE_FEATURE_COMPRESS_USAGE
static const char usage_messages[] ALIGN1 = UNPACKED_USAGE;
#else
# define usage_messages 0
#endif

#if ENABLE_FEATURE_COMPRESS_USAGE

static const char packed_usage[] ALIGN1 = { PACKED_USAGE };
# include "bb_archive.h"
# define unpack_usage_messages() \
	unpack_bz2_data(packed_usage, sizeof(packed_usage), sizeof(UNPACKED_USAGE))
# define dealloc_usage_messages(s) free(s)

#else

# define unpack_usage_messages() usage_messages
# define dealloc_usage_messages(s) ((void)(s))

#endif /* FEATURE_COMPRESS_USAGE */


void FAST_FUNC bb_show_usage(void)
{
	if (ENABLE_SHOW_USAGE) {
#ifdef SINGLE_APPLET_STR
		/* Imagine that this applet is "true". Dont link in printf! */
		const char *usage_string = unpack_usage_messages();

		if (usage_string) {
			if (*usage_string == '\b') {
				full_write2_str("No help available\n");
			} else {
				full_write2_str("Usage: "SINGLE_APPLET_STR" ");
				full_write2_str(usage_string);
				full_write2_str("\n");
			}
			if (ENABLE_FEATURE_CLEAN_UP)
				dealloc_usage_messages((char*)usage_string);
		}
#else
		const char *p;
		const char *usage_string = p = unpack_usage_messages();
		int ap = find_applet_by_name(applet_name);

		if (ap < 0 || usage_string == NULL)
			xfunc_die();
		while (ap) {
			while (*p++) continue;
			ap--;
		}
		full_write2_str(bb_banner);
		full_write2_str(" multi-call binary.\n"); /* common string */
		if (*p == '\b')
			full_write2_str("\nNo help available\n");
		else {
			full_write2_str("\nUsage: ");
			full_write2_str(applet_name);
			if (p[0]) {
				if (p[0] != '\n')
					full_write2_str(" ");
				full_write2_str(p);
			}
			full_write2_str("\n");
		}
		if (ENABLE_FEATURE_CLEAN_UP)
			dealloc_usage_messages((char*)usage_string);
#endif
	}
	xfunc_die();
}

int FAST_FUNC find_applet_by_name(const char *name)
{
	unsigned i, max;
	int j;
	const char *p;

/* The commented-out word-at-a-time code is ~40% faster, but +160 bytes.
 * "Faster" here saves ~0.5 microsecond of real time - not worth it.
 */
#if 0 /*BB_UNALIGNED_MEMACCESS_OK && BB_LITTLE_ENDIAN*/
	uint32_t n32;

	/* Handle all names < 2 chars long early */
	if (name[0] == '\0')
		return -1; /* "" is not a valid applet name */
	if (name[1] == '\0') {
		if (!ENABLE_TEST)
			return -1; /* 1-char name is not valid */
		if (name[0] != ']')
			return -1; /* 1-char name which isn't "[" is not valid */
		/* applet "[" is always applet #0: */
		return 0;
	}
#endif

	p = applet_names;
	i = 0;
#if KNOWN_APPNAME_OFFSETS <= 0
	max = NUM_APPLETS;
#else
	max = NUM_APPLETS * KNOWN_APPNAME_OFFSETS;
	for (j = ARRAY_SIZE(applet_nameofs)-1; j >= 0; j--) {
		const char *pp = applet_names + applet_nameofs[j];
		if (strcmp(name, pp) >= 0) {
			//bb_error_msg("name:'%s' >= pp:'%s'", name, pp);
			p = pp;
			i = max - NUM_APPLETS;
			break;
		}
		max -= NUM_APPLETS;
	}
	max /= (unsigned)KNOWN_APPNAME_OFFSETS;
	i /= (unsigned)KNOWN_APPNAME_OFFSETS;
	//bb_error_msg("name:'%s' starting from:'%s' i:%u max:%u", name, p, i, max);
#endif

	/* Open-coded linear search without strcmp/strlen calls for speed */

#if 0 /*BB_UNALIGNED_MEMACCESS_OK && BB_LITTLE_ENDIAN*/
	/* skip "[\0" name, it's surely not it */
	if (ENABLE_TEST && LONE_CHAR(p, '['))
		i++, p += 2;
	/* All remaining applet names in p[] are at least 2 chars long */
	/* name[] is also at least 2 chars long */

	n32 = (name[0] << 0) | (name[1] << 8) | (name[2] << 16);
	while (i < max) {
		uint32_t p32;
		char ch;

		/* Quickly check match of the first 3 bytes */
		move_from_unaligned32(p32, p);
		p += 3;
		if ((p32 & 0x00ffffff) != n32) {
			/* Most likely case: 3 first bytes do not match */
			i++;
			if ((p32 & 0x00ff0000) == '\0')
				continue; // p[2] was NUL
			p++;
			if ((p32 & 0xff000000) == '\0')
				continue; // p[3] was NUL
			/* p[0..3] aren't matching and none is NUL, check the rest */
			while (*p++ != '\0')
				continue;
			continue;
		}

		/* Unlikely branch: first 3 bytes ([0..2]) match */
		if ((p32 & 0x00ff0000) == '\0') {
			/* name is 2-byte long, it is full match */
			//bb_error_msg("found:'%s' i:%u", name, i);
			return i;
		}
		/* Check remaining bytes [3..NUL] */
		ch = (p32 >> 24);
		j = 3;
		while (ch == name[j]) {
			if (ch == '\0') {
				//bb_error_msg("found:'%s' i:%u", name, i);
				return i;
			}
			ch = *++p;
			j++;
		}
		/* Not a match. Skip it, including NUL */
		while (ch != '\0')
			ch = *++p;
		p++;
		i++;
	}
	return -1;
#else
	while (i < max) {
		char ch;
		j = 0;
		/* Do we see "name\0" in applet_names[p] position? */
		while ((ch = *p) == name[j]) {
			if (ch == '\0') {
				//bb_error_msg("found:'%s' i:%u", name, i);
				return i; /* yes */
			}
			p++;
			j++;
		}
		/* No.
		 * p => 1st non-matching char in applet_names[],
		 * skip to and including NUL.
		 */
		while (ch != '\0')
			ch = *++p;
		p++;
		i++;
	}
	return -1;
#endif
}


void lbb_prepare(const char *applet
		IF_FEATURE_INDIVIDUAL(, char **argv))
				MAIN_EXTERNALLY_VISIBLE;
void lbb_prepare(const char *applet
		IF_FEATURE_INDIVIDUAL(, char **argv))
{
#ifdef __GLIBC__
	(*(int **)&bb_errno) = __errno_location();
	barrier();
#endif
	applet_name = applet;

	if (ENABLE_LOCALE_SUPPORT)
		setlocale(LC_ALL, "");

#if ENABLE_FEATURE_INDIVIDUAL
	/* Redundant for busybox (run_applet_and_exit covers that case)
	 * but needed for "individual applet" mode */
	if (argv[1]
	 && !argv[2]
	 && strcmp(argv[1], "--help") == 0
	 && !is_prefixed_with(applet, "busybox")
	) {
		/* Special case. POSIX says "test --help"
		 * should be no different from e.g. "test --foo".  */
		if (!ENABLE_TEST || strcmp(applet_name, "test") != 0)
			bb_show_usage();
	}
#endif
}

/* The code below can well be in applets/applets.c, as it is used only
 * for busybox binary, not "individual" binaries.
 * However, keeping it here and linking it into libbusybox.so
 * (together with remaining tiny applets/applets.o)
 * makes it possible to avoid --whole-archive at link time.
 * This makes (shared busybox) + libbusybox smaller.
 * (--gc-sections would be even better....)
 */

const char *applet_name;
#if !BB_MMU
bool re_execed;
#endif


/* If not built as a single-applet executable... */
#if !defined(SINGLE_APPLET_MAIN)

IF_FEATURE_SUID(static uid_t ruid;)  /* real uid */

# if ENABLE_FEATURE_SUID_CONFIG

static struct suid_config_t {
	/* next ptr must be first: this struct needs to be llist-compatible */
	struct suid_config_t *m_next;
	struct bb_uidgid_t m_ugid;
	int m_applet;
	mode_t m_mode;
} *suid_config;

static bool suid_cfg_readable;

/* libbb candidate */
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);
}

static void parse_config_file(void)
{
	/* Don't depend on the tools to combine strings. */
	static const char config_file[] ALIGN1 = "/etc/busybox.conf";

	struct suid_config_t *sct_head;
	int applet_no;
	FILE *f;
	const char *errmsg;
	unsigned lc;
	smallint section;
	struct stat st;

	ruid = getuid();
	if (ruid == 0) /* run by root - don't need to even read config file */
		return;

	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_for_read(config_file))  /* Cannot open? */
	) {
		return;
	}

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

	while (1) {
		char buffer[256];
		char *s;

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

		s = buffer;
		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)) {
			errmsg = "line too long";
			goto pe_label;
		}

		/* 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. */
			char *e = strchr(s, ']');
			if (!e   /* Missing right bracket? */
			 || e[1] /* Trailing characters? */
			 || !*(s = get_trimmed_slice(s+1, e)) /* Missing name? */
			) {
				errmsg = "section header";
				goto pe_label;
			}
			/* 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). */
			char *e = strchr(s, '=');
			if (e) {
				s = get_trimmed_slice(s, e);
			}
			if (!e || !*s) {	/* Missing '=' or empty key. */
				errmsg = "keyword";
				goto pe_label;
			}

			/* 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_no = find_applet_by_name(s);
			if (applet_no >= 0) {
				unsigned i;
				struct suid_config_t *sct;

				/* 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 = xzalloc(sizeof(*sct));
				sct->m_applet = applet_no;
				/*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++) {
					/* There are 4 chars for each of user/group/other.
					 * "x-xx" instead of "x-" are to make
					 * "idx > 3" check catch invalid chars.
					 */
					static const char mode_chars[] ALIGN1 = "Ssx-" "Ssx-" "x-xx";
					static const unsigned short mode_mask[] ALIGN2 = {
						S_ISUID, S_ISUID|S_IXUSR, S_IXUSR, 0, /* Ssx- */
						S_ISGID, S_ISGID|S_IXGRP, S_IXGRP, 0, /* Ssx- */
						                          S_IXOTH, 0  /*   x- */
					};
					const char *q = strchrnul(mode_chars + 4*i, *e);
					unsigned idx = q - (mode_chars + 4*i);
					if (idx > 3) {
						errmsg = "mode";
						goto pe_label;
					}
					sct->m_mode |= mode_mask[q - mode_chars];
					e++;
				}

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

				s = skip_whitespace(e);
				/* Default is 0.0, else parse USER.GROUP: */
				if (*s) {
					/* We require whitespace between mode and USER.GROUP */
					if ((s == e) || !(e = strchr(s, '.'))) {
						errmsg = "uid.gid";
						goto pe_label;
					}
					*e = ':'; /* get_uidgid needs USER:GROUP syntax */
					if (get_uidgid(&sct->m_ugid, s) == 0) {
						errmsg = "unknown user/group";
						goto pe_label;
					}
				}
			}
			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) {
			errmsg = "keyword outside section";
			goto pe_label;
		}
	} /* while (1) */

 pe_label:
	fclose(f);
	bb_error_msg("parse error in %s, line %u: %s", config_file, lc, errmsg);

	/* Release any allocated memory before returning. */
	llist_free((llist_t*)sct_head, NULL);
}
# else
static inline void parse_config_file(void)
{
	IF_FEATURE_SUID(ruid = getuid();)
}
# endif /* FEATURE_SUID_CONFIG */


# if ENABLE_FEATURE_SUID && NUM_APPLETS > 0
#  if ENABLE_FEATURE_SUID_CONFIG
/* 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;
}
#  endif

static void check_suid(int applet_no)
{
	gid_t rgid;  /* real gid */

	if (ruid == 0) /* set by parse_config_file() */
		return; /* run by root - no need to check more */
	rgid = getgid();

#  if ENABLE_FEATURE_SUID_CONFIG
	if (suid_cfg_readable) {
		uid_t uid;
		struct suid_config_t *sct;
		mode_t m;

		for (sct = suid_config; sct; sct = sct->m_next) {
			if (sct->m_applet == applet_no)
				goto found;
		}
		goto check_need_suid;
 found:
		/* Is this user allowed to run this applet? */
		m = sct->m_mode;
		if (sct->m_ugid.uid == ruid)
			/* same uid */
			m >>= 6;
		else if ((sct->m_ugid.gid == rgid) || ingroup(ruid, sct->m_ugid.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");

		/* We set effective AND saved ids. If saved-id is not set
		 * like we do below, seteuid(0) can still later succeed! */

		/* Are we directed to change gid
		 * (APPLET = *s* USER.GROUP or APPLET = *S* USER.GROUP)?
		 */
		if (sct->m_mode & S_ISGID)
			rgid = sct->m_ugid.gid;
		/* else: we will set egid = rgid, thus dropping sgid effect */
		if (setresgid(-1, rgid, rgid))
			bb_perror_msg_and_die("setresgid");

		/* Are we directed to change uid
		 * (APPLET = s** USER.GROUP or APPLET = S** USER.GROUP)?
		 */
		uid = ruid;
		if (sct->m_mode & S_ISUID)
			uid = sct->m_ugid.uid;
		/* else: we will set euid = ruid, thus dropping suid effect */
		if (setresuid(-1, uid, uid))
			bb_perror_msg_and_die("setresuid");

		goto ret;
	}
#   if !ENABLE_FEATURE_SUID_CONFIG_QUIET
	{
		static bool onetime = 0;

		if (!onetime) {
			onetime = 1;
			bb_error_msg("using fallback suid method");
		}
	}
#   endif
 check_need_suid:
#  endif
	if (APPLET_SUID(applet_no) == BB_SUID_REQUIRE) {
		/* Real uid is not 0. If euid isn't 0 too, suid bit
		 * is most probably not set on our executable */
		if (geteuid())
			bb_error_msg_and_die("must be suid to work properly");
	} else if (APPLET_SUID(applet_no) == BB_SUID_DROP) {
		/*
		 * Drop all privileges.
		 *
		 * Don't check for errors: in normal use, they are impossible,
		 * and in special cases, exiting is harmful. Example:
		 * 'unshare --user' when user's shell is also from busybox.
		 *
		 * 'unshare --user' creates a new user namespace without any
		 * uid mappings. Thus, busybox binary is setuid nobody:nogroup
		 * within the namespace, as that is the only user. However,
		 * since no uids are mapped, calls to setgid/setuid
		 * fail (even though they would do nothing).
		 */
		setgid(rgid);
		setuid(ruid);
	}
#  if ENABLE_FEATURE_SUID_CONFIG
 ret: ;
	llist_free((llist_t*)suid_config, NULL);
#  endif
}
# else
#  define check_suid(x) ((void)0)
# endif /* FEATURE_SUID */


# if ENABLE_FEATURE_INSTALLER
static const char usr_bin [] ALIGN1 = "/usr/bin/";
static const char usr_sbin[] ALIGN1 = "/usr/sbin/";
static const char *const install_dir[] = {
	&usr_bin [8], /* "/" */
	&usr_bin [4], /* "/bin/" */
	&usr_sbin[4]  /* "/sbin/" */
#  if !ENABLE_INSTALL_NO_USR
	,usr_bin
	,usr_sbin
#  endif
};

/* create (sym)links for each applet */
static void install_links(const char *busybox, int use_symbolic_links,
		char *custom_install_dir)
{
	/* directory table
	 * this should be consistent w/ the enum,
	 * busybox.h::bb_install_loc_t, or else... */
	int (*lf)(const char *, const char *);
	char *fpc;
	const char *appname = applet_names;
	unsigned i;
	int rc;

	lf = link;
	if (use_symbolic_links)
		lf = symlink;

	for (i = 0; i < ARRAY_SIZE(applet_main); i++) {
		fpc = concat_path_file(
				custom_install_dir ? custom_install_dir : install_dir[APPLET_INSTALL_LOC(i)],
				appname);
		// debug: bb_error_msg("%slinking %s to busybox",
		//		use_symbolic_links ? "sym" : "", fpc);
		rc = lf(busybox, fpc);
		if (rc != 0 && errno != EEXIST) {
			bb_simple_perror_msg(fpc);
		}
		free(fpc);
		while (*appname++ != '\0')
			continue;
	}
}
# elif ENABLE_BUSYBOX
static void install_links(const char *busybox UNUSED_PARAM,
		int use_symbolic_links UNUSED_PARAM,
		char *custom_install_dir UNUSED_PARAM)
{
}
# endif

static void run_applet_and_exit(const char *name, char **argv) NORETURN;

# if NUM_SCRIPTS > 0
static int find_script_by_name(const char *name)
{
	int i;
	int applet = find_applet_by_name(name);

	if (applet >= 0) {
		for (i = 0; i < NUM_SCRIPTS; ++i)
			if (applet_numbers[i] == applet)
				return i;
	}
	return -1;
}

int scripted_main(int argc UNUSED_PARAM, char **argv) MAIN_EXTERNALLY_VISIBLE;
int scripted_main(int argc UNUSED_PARAM, char **argv)
{
	int script = find_script_by_name(applet_name);
	if (script >= 0)
#if ENABLE_ASH || ENABLE_SH_IS_ASH || ENABLE_BASH_IS_ASH
		exit(ash_main(-script - 1, argv));
#elif ENABLE_HUSH || ENABLE_SH_IS_HUSH || ENABLE_BASH_IS_HUSH
		exit(hush_main(-script - 1, argv));
#else
		return 1;
#endif
	return 0;
}

char* FAST_FUNC
get_script_content(unsigned n)
{
	char *t = unpack_bz2_data(packed_scripts, sizeof(packed_scripts),
					UNPACKED_SCRIPTS_LENGTH);
	if (t) {
		while (n != 0) {
			while (*t++ != '\0')
				continue;
			n--;
		}
	}
	return t;
}
# endif /* NUM_SCRIPTS > 0 */

# if ENABLE_BUSYBOX
#  if ENABLE_FEATURE_SH_STANDALONE && ENABLE_FEATURE_TAB_COMPLETION
    /*
     * Insert "busybox" into applet table as well.
     * This makes standalone shell tab-complete this name too.
     * (Otherwise having "busybox" in applet table is not necessary,
     * there is other code which routes "busyboxANY_SUFFIX" name
     * to busybox_main()).
     */
//usage:#define busybox_trivial_usage NOUSAGE_STR
//usage:#define busybox_full_usage ""
//applet:IF_BUSYBOX(IF_FEATURE_SH_STANDALONE(IF_FEATURE_TAB_COMPLETION(APPLET(busybox, BB_DIR_BIN, BB_SUID_MAYBE))))
int busybox_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
#  else
#   define busybox_main(argc,argv) busybox_main(argv)
static
#  endif
int busybox_main(int argc UNUSED_PARAM, char **argv)
{
	if (!argv[1]) {
		/* Called without arguments */
		const char *a;
		int col;
		unsigned output_width;
 help:
		output_width = get_terminal_width(2);

		dup2(1, 2);
		full_write2_str(bb_banner); /* reuse const string */
		full_write2_str(" multi-call binary.\n"); /* reuse */
		full_write2_str(
			"BusyBox is copyrighted by many authors between 1998-2015.\n"
			"Licensed under GPLv2. See source distribution for detailed\n"
			"copyright notices.\n"
			"\n"
			"Usage: busybox [function [arguments]...]\n"
			"   or: busybox --list"IF_FEATURE_INSTALLER("[-full]")"\n"
#  if ENABLE_FEATURE_SHOW_SCRIPT && NUM_SCRIPTS > 0
			"   or: busybox --show SCRIPT\n"
#  endif
			IF_FEATURE_INSTALLER(
			"   or: busybox --install [-s] [DIR]\n"
			)
			"   or: function [arguments]...\n"
			"\n"
			IF_NOT_FEATURE_SH_STANDALONE(
			"\tBusyBox is a multi-call binary that combines many common Unix\n"
			"\tutilities into a single executable.  Most people will create a\n"
			"\tlink to busybox for each function they wish to use and BusyBox\n"
			"\twill act like whatever it was invoked as.\n"
			)
			IF_FEATURE_SH_STANDALONE(
			"\tBusyBox is a multi-call binary that combines many common Unix\n"
			"\tutilities into a single executable.  The shell in this build\n"
			"\tis configured to run built-in utilities without $PATH search.\n"
			"\tYou don't need to install a link to busybox for each utility.\n"
			"\tTo run external program, use full path (/sbin/ip instead of ip).\n"
			)
			"\n"
			"Currently defined functions:\n"
		);
		col = 0;
		/* prevent last comma to be in the very last pos */
		output_width--;
		a = applet_names;
		while (*a) {
			int len2 = strlen(a) + 2;
			if (col >= (int)output_width - len2) {
				full_write2_str(",\n");
				col = 0;
			}
			if (col == 0) {
				col = 6;
				full_write2_str("\t");
			} else {
				full_write2_str(", ");
			}
			full_write2_str(a);
			col += len2;
			a += len2 - 1;
		}
		full_write2_str("\n");
		return 0;
	}

#  if ENABLE_FEATURE_SHOW_SCRIPT && NUM_SCRIPTS > 0
	if (strcmp(argv[1], "--show") == 0) {
		int n;
		if (!argv[2])
			bb_error_msg_and_die(bb_msg_requires_arg, "--show");
		n = find_script_by_name(argv[2]);
		if (n < 0)
			bb_error_msg_and_die("script '%s' not found", argv[2]);
		full_write1_str(get_script_content(n));
		return 0;
	}
#  endif

	if (is_prefixed_with(argv[1], "--list")) {
		unsigned i = 0;
		const char *a = applet_names;
		dup2(1, 2);
		while (*a) {
#  if ENABLE_FEATURE_INSTALLER
			if (argv[1][6]) /* --list-full? */
				full_write2_str(install_dir[APPLET_INSTALL_LOC(i)] + 1);
#  endif
			full_write2_str(a);
			full_write2_str("\n");
			i++;
			while (*a++ != '\0')
				continue;
		}
		return 0;
	}

	if (ENABLE_FEATURE_INSTALLER && strcmp(argv[1], "--install") == 0) {
		int use_symbolic_links;
		const char *busybox;

		busybox = xmalloc_readlink(bb_busybox_exec_path);
		if (!busybox) {
			/* bb_busybox_exec_path is usually "/proc/self/exe".
			 * In chroot, readlink("/proc/self/exe") usually fails.
			 * In such case, better use argv[0] as symlink target
			 * if it is a full path name.
			 */
			if (argv[0][0] != '/')
				bb_error_msg_and_die("'%s' is not an absolute path", argv[0]);
			busybox = argv[0];
		}
		/* busybox --install [-s] [DIR]:
		 * -s: make symlinks
		 * DIR: directory to install links to
		 */
		use_symbolic_links = (argv[2] && strcmp(argv[2], "-s") == 0 && ++argv);
		install_links(busybox, use_symbolic_links, argv[2]);
		return 0;
	}

	if (strcmp(argv[1], "--help") == 0) {
		/* "busybox --help [<applet>]" */
		if (!argv[2])
			goto help;
		/* convert to "<applet> --help" */
		argv[0] = argv[2];
		argv[2] = NULL;
	} else {
		/* "busybox <applet> arg1 arg2 ..." */
		argv++;
	}
	/* We support "busybox /a/path/to/applet args..." too. Allows for
	 * "#!/bin/busybox"-style wrappers */
	applet_name = bb_get_last_path_component_nostrip(argv[0]);
	run_applet_and_exit(applet_name, argv);
}
# endif

# if NUM_APPLETS > 0
void FAST_FUNC run_applet_no_and_exit(int applet_no, const char *name, char **argv)
{
	int argc = string_array_len(argv);

	/*
	 * We do not use argv[0]: do not want to repeat massaging of
	 * "-/sbin/halt" -> "halt", for example.
	 */
	applet_name = name;

	/* Special case. POSIX says "test --help"
	 * should be no different from e.g. "test --foo".
	 * Thus for "test", we skip --help check.
	 * "true" and "false" are also special.
	 */
	if (1
#  if defined APPLET_NO_test
	 && applet_no != APPLET_NO_test
#  endif
#  if defined APPLET_NO_true
	 && applet_no != APPLET_NO_true
#  endif
#  if defined APPLET_NO_false
	 && applet_no != APPLET_NO_false
#  endif
	) {
		if (argc == 2 && strcmp(argv[1], "--help") == 0) {
			/* Make "foo --help" exit with 0: */
			xfunc_error_retval = 0;
			bb_show_usage();
		}
	}
	if (ENABLE_FEATURE_SUID)
		check_suid(applet_no);
	xfunc_error_retval = applet_main[applet_no](argc, argv);
	/* Note: applet_main() may also not return (die on a xfunc or such) */
	xfunc_die();
}
# endif /* NUM_APPLETS > 0 */

# if ENABLE_BUSYBOX || NUM_APPLETS > 0
static NORETURN void run_applet_and_exit(const char *name, char **argv)
{
#  if ENABLE_BUSYBOX
	if (is_prefixed_with(name, "busybox"))
		exit(busybox_main(/*unused:*/ 0, argv));
#  endif
#  if NUM_APPLETS > 0
	/* find_applet_by_name() search is more expensive, so goes second */
	{
		int applet = find_applet_by_name(name);
		if (applet >= 0)
			run_applet_no_and_exit(applet, name, argv);
	}
#  endif

	/*bb_error_msg_and_die("applet not found"); - links in printf */
	full_write2_str(applet_name);
	full_write2_str(": applet not found\n");
	/* POSIX: "If a command is not found, the exit status shall be 127" */
	exit(127);
}
# endif

#endif /* !defined(SINGLE_APPLET_MAIN) */


#if ENABLE_BUILD_LIBBUSYBOX
int lbb_main(char **argv)
#else
int main(int argc UNUSED_PARAM, char **argv)
#endif
{
#if 0
	/* TODO: find a use for a block of memory between end of .bss
	 * and end of page. For example, I'm getting "_end:0x812e698 2408 bytes"
	 * - more than 2k of wasted memory (in this particular build)
	 * *per each running process*!
	 * (If your linker does not generate "_end" name, weak attribute
	 * makes &_end == NULL, end_len == 0 here.)
	 */
	extern char _end[] __attribute__((weak));
	unsigned end_len = (-(int)_end) & 0xfff;
	printf("_end:%p %u bytes\n", &_end, end_len);
#endif

	/* Tweak malloc for reduced memory consumption */
#ifdef M_TRIM_THRESHOLD
	/* M_TRIM_THRESHOLD is the maximum amount of freed top-most memory
	 * to keep before releasing to the OS
	 * Default is way too big: 256k
	 */
	mallopt(M_TRIM_THRESHOLD, 8 * 1024);
#endif
#ifdef M_MMAP_THRESHOLD
	/* M_MMAP_THRESHOLD is the request size threshold for using mmap()
	 * Default is too big: 256k
	 */
	mallopt(M_MMAP_THRESHOLD, 32 * 1024 - 256);
#endif
#if 0 /*def M_TOP_PAD*/
	/* When the program break is increased, then M_TOP_PAD bytes are added
	 * to the sbrk(2) request. When the heap is trimmed because of free(3),
	 * this much free space is preserved at the top of the heap.
	 * glibc default seems to be way too big: 128k, but need to verify.
	 */
	mallopt(M_TOP_PAD, 8 * 1024);
#endif

#if !BB_MMU
	/* NOMMU re-exec trick sets high-order bit in first byte of name */
	if (argv[0][0] & 0x80) {
		re_execed = 1;
		argv[0][0] &= 0x7f;
	}
#endif

#if defined(SINGLE_APPLET_MAIN)

	/* Only one applet is selected in .config */
	if (argv[1] && is_prefixed_with(argv[0], "busybox")) {
		/* "busybox <applet> <params>" should still work as expected */
		argv++;
	}
	/* applet_names in this case is just "applet\0\0" */
	lbb_prepare(applet_names IF_FEATURE_INDIVIDUAL(, argv));
# if ENABLE_BUILD_LIBBUSYBOX
	return SINGLE_APPLET_MAIN(string_array_len(argv), argv);
# else
	return SINGLE_APPLET_MAIN(argc, argv);
# endif

#elif !ENABLE_BUSYBOX && NUM_APPLETS == 0

	full_write2_str(bb_basename(argv[0]));
	full_write2_str(": no applets enabled\n");
	exit(127);

#else

	lbb_prepare("busybox" IF_FEATURE_INDIVIDUAL(, argv));
# if !ENABLE_BUSYBOX
	if (argv[1] && is_prefixed_with(bb_basename(argv[0]), "busybox"))
		argv++;
# endif
	applet_name = argv[0];
	if (applet_name[0] == '-')
		applet_name++;
	applet_name = bb_basename(applet_name);

	/* If we are a result of execv("/proc/self/exe"), fix ugly comm of "exe" */
	if (ENABLE_FEATURE_SH_STANDALONE
	 || ENABLE_FEATURE_PREFER_APPLETS
	 || !BB_MMU
	) {
		if (NUM_APPLETS > 1)
			set_task_comm(applet_name);
	}

	parse_config_file(); /* ...maybe, if FEATURE_SUID_CONFIG */
	run_applet_and_exit(applet_name, argv);

#endif
}