-
Notifications
You must be signed in to change notification settings - Fork 6
Expand file tree
/
Copy pathbash-validator.ts
More file actions
627 lines (552 loc) · 18.1 KB
/
Copy pathbash-validator.ts
File metadata and controls
627 lines (552 loc) · 18.1 KB
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
/**
* Bash Command Validator
*
* Uses bash-parser to create a proper AST and validate commands in Plan mode.
* This enables compound commands like `git status && git log` to be allowed
* when all parts are safe, while still blocking dangerous constructs.
*
* AST Node Types:
* - Command: Simple command with name and args
* - LogicalExpression: && (and) or || (or) chains
* - Pipeline: Piped commands (|)
* - Subshell: Commands in parentheses (...)
* - Redirect: File redirections (>, >>, <)
* - CommandExpansion: $(...) substitution
*/
import bashParser from 'bash-parser';
import { debug } from '../utils/debug.ts';
import type { CompiledBashPattern } from './mode-types.ts';
// ============================================================
// Types
// ============================================================
/**
* Result of validating a bash command AST.
* Tracks which subcommands passed/failed for detailed error messages.
*/
export interface BashValidationResult {
allowed: boolean;
/** Primary reason for rejection (if not allowed) */
reason?: BashValidationReason;
/** Individual results for compound commands */
subcommandResults?: SubcommandResult[];
}
export interface SubcommandResult {
/** The command text that was validated */
command: string;
allowed: boolean;
reason?: string;
}
/**
* Detailed reason why validation failed.
* Used to generate helpful error messages.
*/
export type BashValidationReason =
| { type: 'pipeline'; explanation: string }
| { type: 'redirect'; op: string; explanation: string }
| { type: 'command_expansion'; explanation: string }
| { type: 'process_substitution'; explanation: string }
| { type: 'parameter_expansion'; explanation: string }
| { type: 'env_assignment'; explanation: string }
| { type: 'unsafe_command'; command: string; explanation: string }
| { type: 'parse_error'; error: string }
| { type: 'compound_partial_fail'; failedCommands: string[]; passedCommands: string[] }
| { type: 'background_execution'; explanation: string };
// ============================================================
// AST Node Types (from bash-parser)
// ============================================================
interface ASTNode {
type: string;
}
interface WordNode extends ASTNode {
type: 'Word';
text: string;
expansion?: ExpansionNode[];
}
interface CommandNode extends ASTNode {
type: 'Command';
name?: WordNode;
prefix?: ASTNode[];
suffix?: ASTNode[];
/** True if command runs in background with & operator */
async?: boolean;
}
interface LogicalExpressionNode extends ASTNode {
type: 'LogicalExpression';
op: 'and' | 'or';
left: ASTNode;
right: ASTNode;
}
interface PipelineNode extends ASTNode {
type: 'Pipeline';
commands: ASTNode[];
}
interface SubshellNode extends ASTNode {
type: 'Subshell';
list: CompoundListNode;
}
interface CompoundListNode extends ASTNode {
type: 'CompoundList';
commands: ASTNode[];
}
interface RedirectNode extends ASTNode {
type: 'Redirect';
op: { text: string; type: string };
file: WordNode;
}
interface ExpansionNode {
type: string;
command?: string;
commandAST?: ScriptNode;
}
interface ScriptNode extends ASTNode {
type: 'Script';
commands: ASTNode[];
}
// ============================================================
// Dangerous Argument Patterns
// ============================================================
/**
* Command arguments that execute subcommands or perform writes.
* These are program-level features (not shell constructs) that the AST parser
* cannot detect — e.g., `find -exec` runs arbitrary commands despite `find`
* being a read-only search tool.
*
* Checked BEFORE the regex allowlist pattern match in validateCommand().
*/
const DANGEROUS_COMMAND_ARGS: Record<string, Set<string>> = {
find: new Set(['-exec', '-execdir', '-ok', '-okdir', '-delete']),
};
const AWK_COMMANDS = new Set(['awk', 'gawk', 'mawk', 'nawk']);
function getDangerousAwkReason(commandParts: string[]): string | null {
// commandParts[0] is awk/gawk/mawk/nawk - inspect script/args only
const scriptText = commandParts.slice(1).join(' ');
if (/\bsystem\s*\(/i.test(scriptText)) {
return 'awk system() executes arbitrary shell commands';
}
// command | getline executes an external command and reads from it
if (/\|\s*getline\b/i.test(scriptText)) {
return 'awk command pipes to getline execute external commands';
}
// print ... | "cmd" (or with quoted command forms) executes external commands
if (/\bprint\b[^\n]*\|\s*["'`]/i.test(scriptText)) {
return 'awk print-to-command pipes execute external commands';
}
return null;
}
// ============================================================
// Validation Logic
// ============================================================
/**
* Validate a bash command using AST analysis.
*
* @param command - The bash command string to validate
* @param patterns - Compiled regex patterns for allowed commands
* @returns Validation result with detailed reason if rejected
*/
export function validateBashCommand(
command: string,
patterns: CompiledBashPattern[]
): BashValidationResult {
// Parse the command into an AST
let ast: ScriptNode;
try {
ast = bashParser(command) as ScriptNode;
} catch (error) {
debug('[BashValidator] Parse error:', error);
return {
allowed: false,
reason: {
type: 'parse_error',
error: error instanceof Error ? error.message : String(error),
},
};
}
// Validate the AST recursively
const subcommandResults: SubcommandResult[] = [];
const result = validateNode(ast, patterns, subcommandResults);
return {
...result,
subcommandResults: subcommandResults.length > 0 ? subcommandResults : undefined,
};
}
/**
* Recursively validate an AST node.
*/
function validateNode(
node: ASTNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
switch (node.type) {
case 'Script':
return validateScript(node as ScriptNode, patterns, results);
case 'Command':
return validateCommand(node as CommandNode, patterns, results);
case 'LogicalExpression':
return validateLogicalExpression(node as LogicalExpressionNode, patterns, results);
case 'Pipeline':
// Validate each command in the pipeline individually.
// If all commands are in the allowlist, the pipeline is safe.
// e.g., `git log | head` is allowed because both commands are read-only.
return validatePipeline(node as PipelineNode, patterns, results);
case 'Subshell':
return validateSubshell(node as SubshellNode, patterns, results);
case 'CompoundList':
return validateCompoundList(node as CompoundListNode, patterns, results);
default:
// Unknown node type — fail closed. bash-parser may produce node types
// we don't explicitly handle (If, While, For, Case, Function, etc.).
// Block them rather than silently allowing arbitrary constructs.
debug('[BashValidator] Unknown node type (blocked):', node.type);
return {
allowed: false,
reason: {
type: 'parse_error',
error: `Unsupported shell construct: "${node.type}". Only simple commands, pipelines, logical expressions (&&/||), and subshells are supported in Plan mode`,
},
};
}
}
/**
* Validate a Script node (top-level).
*/
function validateScript(
node: ScriptNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
for (const cmd of node.commands) {
const result = validateNode(cmd, patterns, results);
if (!result.allowed) {
return result;
}
}
return { allowed: true };
}
/**
* Validate a simple Command node.
* Checks for:
* 1. Command name matches safe patterns
* 2. No redirects in suffix
* 3. No command expansions in any word
*/
function validateCommand(
node: CommandNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
// Check for background execution (&) - always blocked as it allows
// running commands asynchronously which could hide malicious activity
if (node.async) {
return {
allowed: false,
reason: {
type: 'background_execution',
explanation: 'Background execution (&) runs commands asynchronously which could hide malicious activity',
},
};
}
// Build the full command string for pattern matching
const commandParts: string[] = [];
// Add command name
if (node.name) {
// Check for expansions in command name
const expansionCheck = checkWordForExpansions(node.name);
if (expansionCheck) {
return { allowed: false, reason: expansionCheck };
}
commandParts.push(node.name.text);
}
// Add prefix (assignments, redirects before command)
if (node.prefix) {
for (const item of node.prefix) {
if (item.type === 'Redirect') {
const redirect = item as RedirectNode;
// Allow safe redirects (input redirects and output to /dev/null)
if (!isRedirectSafe(redirect)) {
return {
allowed: false,
reason: {
type: 'redirect',
op: redirect.op.text,
explanation: getRedirectExplanation(redirect.op.text),
},
};
}
}
// Block environment variable assignments in command prefix.
// e.g., PATH=/evil ls, LD_PRELOAD=/evil/lib.so ls, FOO=bar cmd
// These modify the command's environment, potentially enabling
// PATH hijacking or library injection (LD_PRELOAD).
if (item.type === 'AssignmentWord') {
return {
allowed: false,
reason: {
type: 'env_assignment',
explanation: `Environment variable assignment "${(item as WordNode).text}" modifies command behavior (e.g., PATH hijacking, LD_PRELOAD injection)`,
},
};
}
}
}
// Add suffix (arguments, redirects after command)
if (node.suffix) {
for (const item of node.suffix) {
if (item.type === 'Redirect') {
const redirect = item as RedirectNode;
// Allow safe redirects (input redirects and output to /dev/null)
if (!isRedirectSafe(redirect)) {
return {
allowed: false,
reason: {
type: 'redirect',
op: redirect.op.text,
explanation: getRedirectExplanation(redirect.op.text),
},
};
}
} else if (item.type === 'Word') {
const word = item as WordNode;
// Check for command expansions in arguments
const expansionCheck = checkWordForExpansions(word);
if (expansionCheck) {
return { allowed: false, reason: expansionCheck };
}
commandParts.push(word.text);
}
}
}
// Check for command arguments that enable sub-command execution or writes.
// e.g., `find -exec touch file \;` — the `-exec` flag runs arbitrary commands.
// These are program-level features invisible to the shell AST.
const cmdName = node.name?.text;
if (cmdName) {
const normalizedCmd = cmdName.toLowerCase();
if (AWK_COMMANDS.has(normalizedCmd)) {
const awkReason = getDangerousAwkReason(commandParts);
if (awkReason) {
const subResult: SubcommandResult = {
command: commandParts.join(' '),
allowed: false,
reason: awkReason,
};
results.push(subResult);
return {
allowed: false,
reason: {
type: 'unsafe_command',
command: commandParts.join(' '),
explanation: awkReason,
},
};
}
}
if (DANGEROUS_COMMAND_ARGS[normalizedCmd]) {
const dangerousArgs = DANGEROUS_COMMAND_ARGS[normalizedCmd];
for (const part of commandParts) {
if (dangerousArgs.has(part)) {
const subResult: SubcommandResult = {
command: commandParts.join(' '),
allowed: false,
reason: `Argument "${part}" executes subcommands or performs writes`,
};
results.push(subResult);
return {
allowed: false,
reason: {
type: 'unsafe_command',
command: commandParts.join(' '),
explanation: `"${part}" allows arbitrary command execution or file modification within "${normalizedCmd}"`,
},
};
}
}
}
}
// Build the command string and check against patterns
const commandStr = commandParts.join(' ');
// Check if command matches any safe pattern
const matchesPattern = patterns.some(pattern => pattern.regex.test(commandStr));
const subResult: SubcommandResult = {
command: commandStr,
allowed: matchesPattern,
reason: matchesPattern ? undefined : 'Not in read-only allowlist',
};
results.push(subResult);
if (!matchesPattern) {
return {
allowed: false,
reason: {
type: 'unsafe_command',
command: commandStr,
explanation: 'Command is not in the read-only allowlist',
},
};
}
return { allowed: true };
}
/**
* Validate a LogicalExpression (&&, ||).
* Both sides must be valid for the expression to be allowed.
*/
function validateLogicalExpression(
node: LogicalExpressionNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
// Validate left side
const leftResult = validateNode(node.left, patterns, results);
if (!leftResult.allowed) {
return leftResult;
}
// Validate right side
const rightResult = validateNode(node.right, patterns, results);
if (!rightResult.allowed) {
return rightResult;
}
return { allowed: true };
}
/**
* Validate a Pipeline node (cmd1 | cmd2 | ...).
* Each command in the pipeline must be valid for the whole pipeline to be allowed.
*/
function validatePipeline(
node: PipelineNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
for (const cmd of node.commands) {
const result = validateNode(cmd, patterns, results);
if (!result.allowed) {
return result;
}
}
return { allowed: true };
}
/**
* Validate a Subshell node (...).
* The inner commands must all be valid.
*/
function validateSubshell(
node: SubshellNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
return validateNode(node.list, patterns, results);
}
/**
* Validate a CompoundList (list of commands in subshell or similar).
*/
function validateCompoundList(
node: CompoundListNode,
patterns: CompiledBashPattern[],
results: SubcommandResult[]
): BashValidationResult {
for (const cmd of node.commands) {
const result = validateNode(cmd, patterns, results);
if (!result.allowed) {
return result;
}
}
return { allowed: true };
}
/**
* Check a Word node for dangerous expansions.
* Returns a rejection reason if found, null if safe.
*/
function checkWordForExpansions(word: WordNode): BashValidationReason | null {
if (!word.expansion) {
return null;
}
for (const exp of word.expansion) {
if (exp.type === 'CommandExpansion') {
return {
type: 'command_expansion',
explanation: `Command substitution $(...) executes embedded commands (found in: ${word.text})`,
};
}
// Process substitution <(...) or >(...)
// bash-parser may represent these differently, check for common patterns
if (exp.type === 'ProcessSubstitution') {
return {
type: 'process_substitution',
explanation: `Process substitution executes commands (found in: ${word.text})`,
};
}
// Parameter expansion ($VAR, ${VAR}, ${VAR:-default}) can make commands
// behave unpredictably based on environment state.
// e.g., `cat $HOME/.ssh/id_rsa` reads sensitive files via expansion.
if (exp.type === 'ParameterExpansion') {
return {
type: 'parameter_expansion',
explanation: `Variable expansion \${...} makes command behavior dependent on environment state (found in: ${word.text})`,
};
}
}
return null;
}
/**
* Safe input redirect operators that don't write to files.
*/
const SAFE_INPUT_REDIRECTS = new Set([
'<', // Input redirect - read-only
'<&', // Duplicate input file descriptor
]);
/**
* Check if a redirect is safe (read-only or to /dev/null).
*
* Safe redirects:
* - Input redirects: <, <&
* - Output redirects to /dev/null (e.g., >/dev/null, 2>/dev/null)
* - File descriptor duplication (e.g., 2>&1) - just duplicates, doesn't write to file
*/
function isRedirectSafe(redirect: RedirectNode): boolean {
const op = redirect.op.text;
// Input redirects are always safe (read-only)
if (SAFE_INPUT_REDIRECTS.has(op)) {
return true;
}
const target = redirect.file?.text;
// Output redirects to /dev/null are safe
if (target === '/dev/null') {
return true;
}
// File descriptor duplication (e.g., 2>&1) is safe - it just redirects to another fd
// These have targets like "1", "2" (file descriptor numbers)
if (op === '>&' && target && /^\d+$/.test(target)) {
return true;
}
return false;
}
/**
* Get explanation for a redirect operator.
*/
function getRedirectExplanation(op: string): string {
const explanations: Record<string, string> = {
'>': 'overwrites file contents',
'>>': 'appends to file',
'>&': 'redirects file descriptors',
'>|': 'forces overwrite (clobber)',
'<<': 'here-document could inject arbitrary content',
};
return explanations[op] || `redirect operator "${op}" modifies file I/O`;
}
/**
* Check if the command string contains dangerous control characters.
*
* Note: Newlines and carriage returns are NOT blocked here because bash-parser
* correctly parses them as command separators, and the AST validation will
* check each command individually. Only null bytes are blocked as they could
* cause issues at lower levels (C bindings, string handling).
*/
export function hasControlCharacters(command: string): { char: string; explanation: string } | null {
const dangerous: Record<string, string> = {
'\x00': 'Null byte can truncate strings unexpectedly',
};
for (const char of command) {
if (dangerous[char]) {
return { char: '\\0', explanation: dangerous[char] };
}
}
return null;
}