Improve sandbox mode.

15 files changed, 750 insertions, 576 deletions

diff --git a/ChangeLog b/ChangeLog
index 51f9a336..403c72fd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2019-05-06         Arnold D. Robbins     <arnold@skeeve.com>
+
+	In sandbox mode, disallow assigning filenames that weren't
+	there initially. Thanks to Nolan Woods <nolan_w@sfu.ca> for
+	pointing out the gap.
+
+	* awk.h (init_argv_array): Add declaration.
+	* cint_array.c (argv_store): New vtable for ARGV.
+	(argv_shadow_array): New file static variable
+	(argv_store, init_argv_array): New functions.
+	* main.c (init_args): If in sandbox mode, build shadow array of
+	initial argv values. Call init_argv_array.
+
 2019-05-05         Arnold D. Robbins     <arnold@skeeve.com>
 
 	* ext.c (load_ext): Fix the message in the version for when
diff --git a/awk.h b/awk.h
index 19a5eb5f..8d87fc6a 100644
--- a/awk.h
+++ b/awk.h
@@ -1402,6 +1402,7 @@ extern NODE *do_asort(int nargs);
 extern NODE *do_asorti(int nargs);
 extern unsigned long (*hash)(const char *s, size_t len, unsigned long hsize, size_t *code);
 extern void init_env_array(NODE *env_node);
+extern void init_argv_array(NODE *argv_node, NODE *shadow_node);
 /* awkgram.c */
 extern NODE *variable(int location, char *name, NODETYPE type);
 extern int parse_program(INSTRUCTION **pcode, bool from_eval);
diff --git a/cint_array.c b/cint_array.c
index 08815e4e..417f27d5 100644
--- a/cint_array.c
+++ b/cint_array.c
@@ -73,6 +73,24 @@ const array_funcs_t cint_array_func = {
 	(afunc_t) 0,
 };
 
+
+static NODE **argv_store(NODE *symbol, NODE *subs);
+
+/* special case for ARGV in sandbox mode */
+const array_funcs_t argv_array_func = {
+	"argv",
+	cint_array_init,
+	is_uinteger,
+	cint_lookup,
+	cint_exists,
+	cint_clear,
+	cint_remove,
+	cint_list,
+	cint_copy,
+	cint_dump,
+	argv_store,
+};
+
 static inline int cint_hash(long k);
 static inline NODE **cint_find(NODE *symbol, long k, int h1);
 
@@ -1230,3 +1248,68 @@ leaf_print(NODE *array, size_t bi, int indent_level)
 			(unsigned long) array->table_size);
 }
 #endif
+
+static NODE *argv_shadow_array = NULL;
+
+/* argv_store --- post assign function for ARGV in sandbox mode */
+
+static NODE **
+argv_store(NODE *symbol, NODE *subs)
+{
+	NODE **val = cint_exists(symbol, subs);
+	NODE *newval = *val;
+	char *cp;
+
+	if (newval->stlen == 0)	// empty strings in ARGV are OK
+		return val;
+
+	if ((cp = strchr(newval->stptr, '=')) == NULL) {
+		if (! in_array(argv_shadow_array, newval))
+			fatal(_("cannot add a new file (%.*s) to ARGV in sandbox mode"),
+				(int) newval->stlen, newval->stptr);
+	} else {
+		// check if it's a valid variable assignment
+		bool badvar = false;
+		char *arg = newval->stptr;
+		char *cp2;
+
+		*cp = '\0';	// temporarily
+
+		if (! is_letter((unsigned char) arg[0]))
+			badvar = true;
+		else
+			for (cp2 = arg+1; *cp2; cp2++)
+				if (! is_identchar((unsigned char) *cp2) && *cp2 != ':') {
+					badvar = true;
+					break;
+				}
+
+		// further checks
+		if (! badvar) {
+			char *cp = strchr(arg, ':');
+			if (cp && (cp[1] != ':' || strchr(cp + 2, ':') != NULL))
+				badvar = true;
+		}
+		*cp = '=';	// restore the '='
+
+		if (badvar && ! in_array(argv_shadow_array, newval))
+			fatal(_("cannot add a new file (%.*s) to ARGV in sandbox mode"),
+				(int) newval->stlen, newval->stptr);
+
+		// otherwise, badvar is false, let it through as variable assignment
+	}
+	return val;
+}
+
+/* init_argv_array --- set up the pointers for ARGV in sandbox mode. A bit hacky. */
+
+void
+init_argv_array(NODE *argv_node, NODE *shadow_node)
+{
+	/* If POSIX simply don't reset the vtable and things work as before */
+	if (! do_sandbox)
+		return;
+
+	argv_node->array_funcs = & argv_array_func;
+	argv_shadow_array = shadow_node;
+}
diff --git a/doc/ChangeLog b/doc/ChangeLog
index 962656fb..6220648d 100644
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -2,6 +2,8 @@
 
 	* gawktexi.in: Fix some typos.  Thanks to Mark Krauze
 	<daburashka@ya.ru>, for pointing them out.
+	(Options): Document new feature in --sandbox, that you can't
+	add files that weren't there to start with.
 
 2019-05-05         Arnold D. Robbins     <arnold@skeeve.com>
 
diff --git a/doc/gawk.info b/doc/gawk.info
index a657dfcd..d68921c0 100644
--- a/doc/gawk.info
+++ b/doc/gawk.info
@@ -2784,10 +2784,11 @@ The following list describes options mandated by the POSIX standard:
 '--sandbox'
      Disable the 'system()' function, input redirections with 'getline',
      output redirections with 'print' and 'printf', and dynamic
-     extensions.  This is particularly useful when you want to run 'awk'
-     scripts from questionable sources and need to make sure the scripts
-     can't access your system (other than the specified input data
-     file).
+     extensions.  Also, disallow adding filenames to 'ARGV' that were
+     not there when 'gawk' started running.  This is particularly useful
+     when you want to run 'awk' scripts from questionable sources and
+     need to make sure the scripts can't access your system (other than
+     the specified input data file).
 
 '-t'
 '--lint-old'
@@ -29248,8 +29249,8 @@ Info file, in approximate chronological order:
 
    * Anders Wallin helped keep the VMS port going for several years.
 
-   * Assaf Gordon contributed the code to implement the '--sandbox'
-     option.
+   * Assaf Gordon contributed the initial code to implement the
+     '--sandbox' option.
 
    * John Haque made the following contributions:
 
@@ -33685,7 +33686,7 @@ Index
 * --include option:                      Options.             (line 181)
 * --lint option:                         Command Line.        (line  20)
 * --lint option <1>:                     Options.             (line 210)
-* --lint-old option:                     Options.             (line 324)
+* --lint-old option:                     Options.             (line 325)
 * --load option:                         Options.             (line 198)
 * --no-optimize option:                  Options.             (line 310)
 * --non-decimal-data option:             Options.             (line 235)
@@ -33709,7 +33710,7 @@ Index
 * --traditional option:                  Options.             (line  86)
 * --traditional option, --posix option and: Options.          (line 297)
 * --use-lc-numeric option:               Options.             (line 244)
-* --version option:                      Options.             (line 329)
+* --version option:                      Options.             (line 330)
 * -b option:                             Options.             (line  73)
 * -c option:                             Options.             (line  86)
 * -C option:                             Options.             (line  93)
@@ -33717,20 +33718,20 @@ Index
 * -D option:                             Options.             (line 112)
 * -e option:                             Options.             (line 121)
 * -E option:                             Options.             (line 147)
-* -e option <1>:                         Options.             (line 365)
+* -e option <1>:                         Options.             (line 366)
 * -f option:                             Long.                (line  12)
 * -F option:                             Options.             (line  21)
 * -f option <1>:                         Options.             (line  25)
-* -F option, -Ft sets FS to TAB:         Options.             (line 337)
+* -F option, -Ft sets FS to TAB:         Options.             (line 338)
 * -F option, command-line:               Command Line Field Separator.
                                                               (line   6)
-* -f option, multiple uses:              Options.             (line 342)
+* -f option, multiple uses:              Options.             (line 343)
 * -g option:                             Options.             (line 169)
 * -h option:                             Options.             (line 176)
 * -i option:                             Options.             (line 181)
 * -l option:                             Options.             (line 198)
 * -l option <1>:                         Options.             (line 210)
-* -L option:                             Options.             (line 324)
+* -L option:                             Options.             (line 325)
 * -M option:                             Options.             (line 229)
 * -n option:                             Options.             (line 235)
 * -N option:                             Options.             (line 244)
@@ -33742,7 +33743,7 @@ Index
 * -s option:                             Options.             (line 310)
 * -S option:                             Options.             (line 315)
 * -v option:                             Options.             (line  36)
-* -V option:                             Options.             (line 329)
+* -V option:                             Options.             (line 330)
 * -v option <1>:                         Assignment Options.  (line  12)
 * -W option:                             Options.             (line  51)
 * . (period), regexp operator:           Regexp Operator Details.
@@ -33971,6 +33972,7 @@ Index
 * arguments, command-line, invoking awk: Command Line.        (line   6)
 * arguments, in function calls:          Function Calls.      (line  18)
 * arguments, processing:                 Getopt Function.     (line   6)
+* ARGV array:                            Options.             (line 315)
 * ARGV array, indexing into:             Other Arguments.     (line  15)
 * arithmetic operators:                  Arithmetic Ops.      (line   6)
 * array manipulation in extensions:      Array Manipulation.  (line   6)
@@ -34491,7 +34493,7 @@ Index
 * cosine:                                Numeric Functions.   (line  16)
 * counting:                              Wc Program.          (line   6)
 * csh utility:                           Statements/Lines.    (line  43)
-* csh utility, POSIXLY_CORRECT environment variable: Options. (line 386)
+* csh utility, POSIXLY_CORRECT environment variable: Options. (line 387)
 * csh utility, |& operator, comparison with: Two-way I/O.     (line  27)
 * ctime() user-defined function:         Function Example.    (line  74)
 * Curreli, Marco:                        Contributors.        (line 147)
@@ -35339,7 +35341,7 @@ Index
 * gawk, TEXTDOMAIN variable in:          User-modified.       (line 155)
 * gawk, timestamps:                      Time Functions.      (line   6)
 * gawk, uses for:                        Preface.             (line  34)
-* gawk, versions of, information about, printing: Options.    (line 329)
+* gawk, versions of, information about, printing: Options.    (line 330)
 * gawk, VMS version of:                  VMS Installation.    (line   6)
 * gawk, word-boundary operator:          GNU Regexp Operators.
                                                               (line  66)
@@ -35673,7 +35675,7 @@ Index
 * lint checking, empty programs:         Command Line.        (line  16)
 * lint checking, issuing warnings:       Options.             (line 210)
 * lint checking, POSIXLY_CORRECT environment variable: Options.
-                                                              (line 371)
+                                                              (line 372)
 * lint checking, undefined functions:    Function Caveats.    (line  23)
 * LINT variable:                         User-modified.       (line  90)
 * Linux:                                 Manual History.      (line  28)
@@ -36035,7 +36037,7 @@ Index
 * portability, NF variable, decrementing: Changing Fields.    (line 115)
 * portability, operators:                Increment Ops.       (line  60)
 * portability, operators, not in POSIX awk: Precedence.       (line  97)
-* portability, POSIXLY_CORRECT environment variable: Options. (line 391)
+* portability, POSIXLY_CORRECT environment variable: Options. (line 392)
 * portability, substr() function:        String Functions.    (line 518)
 * portable object files:                 Explaining gettext.  (line  37)
 * portable object files <1>:             Translator i18n.     (line   6)
@@ -36087,11 +36089,11 @@ Index
 * POSIX awk, timestamps and:             Time Functions.      (line   6)
 * POSIX awk, | I/O operator and:         Getline/Pipe.        (line  56)
 * POSIX mode:                            Options.             (line 282)
-* POSIX mode <1>:                        Options.             (line 371)
+* POSIX mode <1>:                        Options.             (line 372)
 * POSIX, awk and:                        Preface.             (line  21)
 * POSIX, gawk extensions not included in: POSIX/GNU.          (line   6)
 * POSIX, programs, implementing in awk:  Clones.              (line   6)
-* POSIXLY_CORRECT environment variable:  Options.             (line 371)
+* POSIXLY_CORRECT environment variable:  Options.             (line 372)
 * PREC variable:                         User-modified.       (line 127)
 * precedence:                            Increment Ops.       (line  60)
 * precedence <1>:                        Precedence.          (line   6)
@@ -36936,557 +36938,557 @@ Node: Intro Summary116293
 Node: Invoking Gawk117177
 Node: Command Line118691
 Node: Options119489
-Ref: Options-Footnote-1136754
-Ref: Options-Footnote-2136985
-Node: Other Arguments137010
-Node: Naming Standard Input139957
-Node: Environment Variables141167
-Node: AWKPATH Variable141725
-Ref: AWKPATH Variable-Footnote-1145137
-Ref: AWKPATH Variable-Footnote-2145171
-Node: AWKLIBPATH Variable145432
-Node: Other Environment Variables147090
-Node: Exit Status150911
-Node: Include Files151588
-Node: Loading Shared Libraries155278
-Node: Obsolete156706
-Node: Undocumented157398
-Node: Invoking Summary157695
-Node: Regexp159355
-Node: Regexp Usage160809
-Node: Escape Sequences162846
-Node: Regexp Operators169078
-Node: Regexp Operator Details169563
-Ref: Regexp Operator Details-Footnote-1175685
-Node: Interval Expressions175832
-Ref: Interval Expressions-Footnote-1177267
-Node: Bracket Expressions177365
-Ref: table-char-classes179841
-Node: Leftmost Longest183167
-Node: Computed Regexps184470
-Node: GNU Regexp Operators187897
-Node: Case-sensitivity191576
-Ref: Case-sensitivity-Footnote-1194442
-Ref: Case-sensitivity-Footnote-2194677
-Node: Regexp Summary194785
-Node: Reading Files196251
-Node: Records198520
-Node: awk split records199595
-Node: gawk split records204870
-Ref: gawk split records-Footnote-1209456
-Node: Fields209493
-Node: Nonconstant Fields212234
-Ref: Nonconstant Fields-Footnote-1214470
-Node: Changing Fields214674
-Node: Field Separators220705
-Node: Default Field Splitting223403
-Node: Regexp Field Splitting224521
-Node: Single Character Fields227874
-Node: Command Line Field Separator228934
-Node: Full Line Fields232152
-Ref: Full Line Fields-Footnote-1233674
-Ref: Full Line Fields-Footnote-2233720
-Node: Field Splitting Summary233821
-Node: Constant Size235895
-Node: Fixed width data236627
-Node: Skipping intervening240094
-Node: Allowing trailing data240892
-Node: Fields with fixed data241929
-Node: Splitting By Content243447
-Ref: Splitting By Content-Footnote-1247097
-Node: Testing field creation247260
-Node: Multiple Line248885
-Node: Getline255162
-Node: Plain Getline257631
-Node: Getline/Variable260272
-Node: Getline/File261423
-Node: Getline/Variable/File262811
-Ref: Getline/Variable/File-Footnote-1264416
-Node: Getline/Pipe264504
-Node: Getline/Variable/Pipe267211
-Node: Getline/Coprocess268346
-Node: Getline/Variable/Coprocess269613
-Node: Getline Notes270355
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-Ref: table-getline-variants273576
-Node: Read Timeout274324
-Ref: Read Timeout-Footnote-1278230
-Node: Retrying Input278288
-Node: Command-line directories279487
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-Node: Input Exercises283565
-Node: Printing284293
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-Node: Print Examples287584
-Node: Output Separators290364
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-Node: Special Caveats322322
-Node: Close Files And Pipes323271
-Ref: table-close-pipe-return-values330178
-Ref: Close Files And Pipes-Footnote-1330991
-Ref: Close Files And Pipes-Footnote-2331139
-Node: Nonfatal331291
-Node: Output Summary333629
-Node: Output Exercises334851
-Node: Expressions335530
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-Node: Scalar Constants338087
-Ref: Scalar Constants-Footnote-1340611
-Node: Nondecimal-numbers340861
-Node: Regexp Constants343862
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-Node: Standard Regexp Constants345010
-Node: Strong Regexp Constants348198
-Node: Variables351156
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-Ref: Strings And Numbers-Footnote-1359777
-Node: Locale influences conversions359886
-Ref: table-locale-affects362644
-Node: All Operators363262
-Node: Arithmetic Ops363891
-Node: Concatenation366397
-Ref: Concatenation-Footnote-1369244
-Node: Assignment Ops369351
-Ref: table-assign-ops374342
-Node: Increment Ops375655
-Node: Truth Values and Conditions379115
-Node: Truth Values380189
-Node: Typing and Comparison381237
-Node: Variable Typing382057
-Ref: Variable Typing-Footnote-1388520
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-Node: Conditional Exp399075
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-Node: Locales408347
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-Node: Patterns and Actions412552
-Node: Pattern Overview413672
-Node: Regexp Patterns415349
-Node: Expression Patterns415891
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-Ref: Egrep Program-Footnote-1735458
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-Ref: Split Program-Footnote-1742706
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-Node: Miscellaneous Programs757595
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-Ref: Controlling Array Traversal-Footnote-1828160
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-Node: TCP/IP Networking841555
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-Node: I18N and L10N857012
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-Ref: Explaining gettext-Footnote-1863591
-Ref: Explaining gettext-Footnote-2863776
-Node: Programmer i18n863941
-Ref: Programmer i18n-Footnote-1868890
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+Node: Extension Sample Fnmatch1118848
+Node: Extension Sample Fork1120335
+Node: Extension Sample Inplace1121553
+Node: Extension Sample Ord1124857
+Node: Extension Sample Readdir1125693
+Ref: table-readdir-file-types1126582
+Node: Extension Sample Revout1127387
+Node: Extension Sample Rev2way1127976
+Node: Extension Sample Read write array1128716
+Node: Extension Sample Readfile1130658
+Node: Extension Sample Time1131753
+Node: Extension Sample API Tests1133101
+Node: gawkextlib1133593
+Node: Extension summary1136511
+Node: Extension Exercises1140213
+Node: Language History1141455
+Node: V7/SVR3.11143111
+Node: SVR41145263
+Node: POSIX1146697
+Node: BTL1148077
+Node: POSIX/GNU1148806
+Node: Feature History1154584
+Node: Common Extensions1170630
+Node: Ranges and Locales1171913
+Ref: Ranges and Locales-Footnote-11176529
+Ref: Ranges and Locales-Footnote-21176556
+Ref: Ranges and Locales-Footnote-31176791
+Node: Contributors1177012
+Node: History summary1182965
+Node: Installation1184345
+Node: Gawk Distribution1185289
+Node: Getting1185773
+Node: Extracting1186736
+Node: Distribution contents1188374
+Node: Unix Installation1194854
+Node: Quick Installation1195536
+Node: Shell Startup Files1197950
+Node: Additional Configuration Options1199039
+Node: Configuration Philosophy1201354
+Node: Non-Unix Installation1203723
+Node: PC Installation1204183
+Node: PC Binary Installation1205021
+Node: PC Compiling1205456
+Node: PC Using1206573
+Node: Cygwin1210126
+Node: MSYS1211225
+Node: VMS Installation1211726
+Node: VMS Compilation1212517
+Ref: VMS Compilation-Footnote-11213746
+Node: VMS Dynamic Extensions1213804
+Node: VMS Installation Details1215489
+Node: VMS Running1217742
+Node: VMS GNV1222021
+Node: VMS Old Gawk1222756
+Node: Bugs1223227
+Node: Bug address1223890
+Node: Usenet1226872
+Node: Maintainers1227876
+Node: Other Versions1229137
+Node: Installation summary1236225
+Node: Notes1237427
+Node: Compatibility Mode1238221
+Node: Additions1239003
+Node: Accessing The Source1239928
+Node: Adding Code1241365
+Node: New Ports1247584
+Node: Derived Files1251959
+Ref: Derived Files-Footnote-11257619
+Ref: Derived Files-Footnote-21257654
+Ref: Derived Files-Footnote-31258252
+Node: Future Extensions1258366
+Node: Implementation Limitations1259024
+Node: Extension Design1260207
+Node: Old Extension Problems1261351
+Ref: Old Extension Problems-Footnote-11262869
+Node: Extension New Mechanism Goals1262926
+Ref: Extension New Mechanism Goals-Footnote-11266290
+Node: Extension Other Design Decisions1266479
+Node: Extension Future Growth1268592
+Node: Notes summary1269428
+Node: Basic Concepts1270586
+Node: Basic High Level1271267
+Ref: figure-general-flow1271549
+Ref: figure-process-flow1272234
+Ref: Basic High Level-Footnote-11275535
+Node: Basic Data Typing1275720
+Node: Glossary1279048
+Node: Copying1310886
+Node: GNU Free Documentation License1348429
+Node: Index1373549
 
 End Tag Table
diff --git a/doc/gawk.texi b/doc/gawk.texi
index d56261b6..0844b80c 100644
--- a/doc/gawk.texi
+++ b/doc/gawk.texi
@@ -4271,10 +4271,13 @@ representation of the program.
 @cindex @option{-S} option
 @cindex @option{--sandbox} option
 @cindex sandbox mode
+@cindex @code{ARGV} array
 Disable the @code{system()} function,
 input redirections with @code{getline},
 output redirections with @code{print} and @code{printf},
 and dynamic extensions.
+Also, disallow adding filenames to @code{ARGV} that were
+not there when @command{gawk} started running.
 This is particularly useful when you want to run @command{awk} scripts
 from questionable sources and need to make sure the scripts
 can't access your system (other than the specified input @value{DF}).
@@ -39955,7 +39958,7 @@ Anders Wallin helped keep the VMS port going for several years.
 
 @item
 @cindex Gordon, Assaf
-Assaf Gordon contributed the code to implement the
+Assaf Gordon contributed the initial code to implement the
 @option{--sandbox} option.
 
 @item
diff --git a/doc/gawktexi.in b/doc/gawktexi.in
index 5487bb7f..80650513 100644
--- a/doc/gawktexi.in
+++ b/doc/gawktexi.in
@@ -4181,10 +4181,13 @@ representation of the program.
 @cindex @option{-S} option
 @cindex @option{--sandbox} option
 @cindex sandbox mode
+@cindex @code{ARGV} array
 Disable the @code{system()} function,
 input redirections with @code{getline},
 output redirections with @code{print} and @code{printf},
 and dynamic extensions.
+Also, disallow adding filenames to @code{ARGV} that were
+not there when @command{gawk} started running.
 This is particularly useful when you want to run @command{awk} scripts
 from questionable sources and need to make sure the scripts
 can't access your system (other than the specified input @value{DF}).
@@ -38928,7 +38931,7 @@ Anders Wallin helped keep the VMS port going for several years.
 
 @item
 @cindex Gordon, Assaf
-Assaf Gordon contributed the code to implement the
+Assaf Gordon contributed the initial code to implement the
 @option{--sandbox} option.
 
 @item
diff --git a/main.c b/main.c
index 8327cc74..1f23e57c 100644
--- a/main.c
+++ b/main.c
@@ -749,6 +749,7 @@ init_args(int argc0, int argc, const char *argv0, char **argv)
 {
 	int i, j;
 	NODE *sub, *val;
+	NODE *shadow_node = NULL;
 
 	ARGV_node = install_symbol(estrdup("ARGV", 4), Node_var_array);
 	sub = make_number(0.0);
@@ -756,15 +757,32 @@ init_args(int argc0, int argc, const char *argv0, char **argv)
 	val->flags |= USER_INPUT;
 	assoc_set(ARGV_node, sub, val);
 
+	if (do_sandbox) {
+		shadow_node = make_array();
+		sub = make_string(argv0, strlen(argv0));
+		val = make_number(0.0);
+		assoc_set(shadow_node, sub, val);
+	}
+
+
 	for (i = argc0, j = 1; i < argc; i++, j++) {
 		sub = make_number((AWKNUM) j);
 		val = make_string(argv[i], strlen(argv[i]));
 		val->flags |= USER_INPUT;
 		assoc_set(ARGV_node, sub, val);
+
+		if (do_sandbox) {
+			sub = make_string(argv[i], strlen(argv[i]));
+			val = make_number(0.0);
+			assoc_set(shadow_node, sub, val);
+		}
 	}
 
 	ARGC_node = install_symbol(estrdup("ARGC", 4), Node_var);
 	ARGC_node->var_value = make_number((AWKNUM) j);
+
+	if (do_sandbox)
+		init_argv_array(ARGV_node, shadow_node);
 }
 
 
diff --git a/test/ChangeLog b/test/ChangeLog
index e5b9dce2..c3d7475f 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,6 +1,13 @@
+2019-05-06         Arnold D. Robbins     <arnold@skeeve.com>
+
+	* Makefile.am (EXTRA_DIST): New test: sandbox1.
+	(NEED_SANDBOX): New list of tests.
+	* Gentests: Handle NEED_SANDBOX.
+	* sandbox1.awk, sandbox1.ok: New files.
+
 2019-02-22         Andrew J. Schorr     <aschorr@telemetry-investments.com>
 
-	* Makefile.am (EXTRA_DIST): New test assignnumfield2.
+	* Makefile.am (EXTRA_DIST): New test: assignnumfield2.
 	* assignnumfield2.awk, assignnumfield2.ok: New files.
 
 2019-04-21         Arnold D. Robbins     <arnold@skeeve.com>
diff --git a/test/Gentests b/test/Gentests
index cf4ba908..9f51b927 100755
--- a/test/Gentests
+++ b/test/Gentests
@@ -94,6 +94,13 @@ BEGIN {
 	next
 }
 
+/^NEED_SANDBOX *=/,/[^\\]$/ {
+	gsub(/(^NEED_SANDBOX *=|\\$)/,"")
+	for (i = 1; i <= NF; i++)
+		sandbox[$i]
+	next
+}
+
 /^GENTESTS_UNUSED *=/,/[^\\]$/ {
 	gsub(/(^GENTESTS_UNUSED *=|\\$)/,"")
 	for (i = 1; i <= NF; i++)
@@ -204,6 +211,10 @@ function generate(x,	s, i, locale_string)
 		s = s " --traditional"
 		delete traditional[x]
 	}
+	if (x in sandbox) {
+		s = s " --sandbox"
+		delete sandbox[x]
+	}
 	if (x in pretty) {
 		s = s " --pretty-print=_$@"
 		delete pretty[x]
diff --git a/test/Makefile.am b/test/Makefile.am
index 4a5ab2d2..3db7c04d 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -1067,6 +1067,8 @@ EXTRA_DIST = \
 	rwarray.awk \
 	rwarray.in \
 	rwarray.ok \
+	sandbox1.awk \
+	sandbox1.ok \
 	scalar.awk \
 	scalar.ok \
 	sclforin.awk \
@@ -1354,7 +1356,8 @@ GAWK_EXT_TESTS = \
 	profile7 profile8 profile9 profile10 profile11 profile12 pty1 pty2 \
 	rebuf regnul1 regnul2 regx8bit reginttrad reint reint2 rsgetline rsglstdin \
 	rsstart1 rsstart2 rsstart3 rstest6 \
-	shadow shadowbuiltin sortfor sortfor2 sortu sourcesplit split_after_fpat \
+	sandbox1 shadow shadowbuiltin sortfor sortfor2 sortu \
+	sourcesplit split_after_fpat \
 	splitarg4 strftfld strftime strtonum strtonum1 switch2 symtab1 symtab2 \
 	symtab3 symtab4 symtab5 symtab6 symtab7 symtab8 symtab9 symtab10 \
 	timeout typedregex1 typedregex2 typedregex3 typedregex4 \
@@ -1414,6 +1417,9 @@ NEED_PRETTY = nsprof1 nsprof2 \
 # List of tests that need --re-interval
 NEED_RE_INTERVAL = gsubtst3 reint reint2
 
+# List of tests that need --sandbox
+NEED_SANDBOX = sandbox1
+
 # List of tests that need --traditional
 NEED_TRADITIONAL = litoct tradanch rscompat
 
diff --git a/test/Makefile.in b/test/Makefile.in
index bd261a5b..5496d3cf 100644
--- a/test/Makefile.in
+++ b/test/Makefile.in
@@ -1326,6 +1326,8 @@ EXTRA_DIST = \
 	rwarray.awk \
 	rwarray.in \
 	rwarray.ok \
+	sandbox1.awk \
+	sandbox1.ok \
 	scalar.awk \
 	scalar.ok \
 	sclforin.awk \
@@ -1613,7 +1615,8 @@ GAWK_EXT_TESTS = \
 	profile7 profile8 profile9 profile10 profile11 profile12 pty1 pty2 \
 	rebuf regnul1 regnul2 regx8bit reginttrad reint reint2 rsgetline rsglstdin \
 	rsstart1 rsstart2 rsstart3 rstest6 \
-	shadow shadowbuiltin sortfor sortfor2 sortu sourcesplit split_after_fpat \
+	sandbox1 shadow shadowbuiltin sortfor sortfor2 sortu \
+	sourcesplit split_after_fpat \
 	splitarg4 strftfld strftime strtonum strtonum1 switch2 symtab1 symtab2 \
 	symtab3 symtab4 symtab5 symtab6 symtab7 symtab8 symtab9 symtab10 \
 	timeout typedregex1 typedregex2 typedregex3 typedregex4 \
@@ -1673,6 +1676,9 @@ NEED_PRETTY = nsprof1 nsprof2 \
 # List of tests that need --re-interval
 NEED_RE_INTERVAL = gsubtst3 reint reint2
 
+# List of tests that need --sandbox
+NEED_SANDBOX = sandbox1
+
 # List of tests that need --traditional
 NEED_TRADITIONAL = litoct tradanch rscompat
 
@@ -4591,6 +4597,11 @@ rstest6:
 	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  < "$(srcdir)"/$@.in >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
 	@-$(CMP) "$(srcdir)"/$@.ok _$@ && rm -f _$@
 
+sandbox1:
+	@echo $@
+	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  --sandbox >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
+	@-$(CMP) "$(srcdir)"/$@.ok _$@ && rm -f _$@
+
 shadow:
 	@echo $@
 	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  --lint >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
diff --git a/test/Maketests b/test/Maketests
index ccce4f54..cf85ef8d 100644
--- a/test/Maketests
+++ b/test/Maketests
@@ -1846,6 +1846,11 @@ rstest6:
 	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  < "$(srcdir)"/$@.in >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
 	@-$(CMP) "$(srcdir)"/$@.ok _$@ && rm -f _$@
 
+sandbox1:
+	@echo $@
+	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  --sandbox >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
+	@-$(CMP) "$(srcdir)"/$@.ok _$@ && rm -f _$@
+
 shadow:
 	@echo $@
 	@AWKPATH="$(srcdir)" $(AWK) -f $@.awk  --lint >_$@ 2>&1 || echo EXIT CODE: $$? >>_$@
diff --git a/test/sandbox1.awk b/test/sandbox1.awk
new file mode 100644
index 00000000..e84894d7
--- /dev/null
+++ b/test/sandbox1.awk
@@ -0,0 +1,7 @@
+BEGIN {
+	ARGV[ARGC++] = ARGV[1]	# should be ok
+	ARGV[ARGC++] = ""	# empty string, should be ok
+	ARGV[ARGC++] = "foo=bar"	# assignment, should be ok
+	ARGV[ARGC++] = "junk::foo=bar"	# assignment, should be ok
+	ARGV[ARGC++] = "/dev/null"	# should fatal here
+}
diff --git a/test/sandbox1.ok b/test/sandbox1.ok
new file mode 100644
index 00000000..210b7261
--- /dev/null
+++ b/test/sandbox1.ok
@@ -0,0 +1,2 @@
+gawk: sandbox1.awk:6: fatal: cannot add a new file (/dev/null) to ARGV in sandbox mode
+EXIT CODE: 2