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Error, rather than warn, once a number of invalid path operators are encountered in EvaluatorPreprocessor.read (bug 1443140)

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Incomplete path operators, in particular, can result in fairly chaotic rendering artifacts, as can be observed on page four of the referenced PDF file.

The initial (naive) solution that was attempted, was to simply throw a `FormatError` as soon as any invalid (i.e. too short) operator was found and rely on the existing `ignoreErrors` code-paths. However, doing so would have caused regressions in some files; see the existing `issue2391-1` test-case, which was promoted to an `eq` test to help prevent future bugs.
Hence this patch, which adds special handling for invalid path operators since those may cause quite bad rendering artifacts.

You could, in all fairness, argue that the patch is a handwavy solution and I wouldn't object. However, given that this only concerns *corrupt* PDF files, the way that PDF viewers (PDF.js included) try to gracefully deal with those could probably be described as a best-effort solution anyway.

This patch also adjusts the existing `warn`/`info` messages to print the command name according to the PDF specification, rather than an internal PDF.js enumeration value. The former should be much more useful for debugging purposes.

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1443140.
This commit is contained in:
Jonas Jenwald 2018-06-24 09:53:32 +02:00
parent e8b5088370
commit 7f21e38787
4 changed files with 57 additions and 7 deletions
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23
src/core/evaluator.js
View File

@ -2932,6 +2932,8 @@ var EvaluatorPreprocessor = (function EvaluatorPreprocessorClosure() {
t['null'] = null;
});
const MAX_INVALID_PATH_OPS = 20;
function EvaluatorPreprocessor(stream, xref, stateManager) {
this.opMap = getOPMap();
// TODO(mduan): pass array of knownCommands rather than this.opMap
@ -2939,6 +2941,7 @@ var EvaluatorPreprocessor = (function EvaluatorPreprocessorClosure() {
this.parser = new Parser(new Lexer(stream, this.opMap), false, xref);
this.stateManager = stateManager;
this.nonProcessedArgs = [];
this._numInvalidPathOPS = 0;
}
EvaluatorPreprocessor.prototype = {
@ -2976,7 +2979,7 @@ var EvaluatorPreprocessor = (function EvaluatorPreprocessorClosure() {
// Check that the command is valid
var opSpec = this.opMap[cmd];
if (!opSpec) {
warn('Unknown command "' + cmd + '"');
warn(`Unknown command "${cmd}".`);
continue;
}
@ -3002,18 +3005,28 @@ var EvaluatorPreprocessor = (function EvaluatorPreprocessorClosure() {
}
if (argsLength < numArgs) {
const partialMsg = `command ${cmd}: expected ${numArgs} args, ` +
`but received ${argsLength} args.`;
// Incomplete path operators, in particular, can result in fairly
// chaotic rendering artifacts. Hence the following heuristics is
// used to error, rather than just warn, once a number of invalid
// path operators have been encountered (fixes bug1443140.pdf).
if ((fn >= OPS.moveTo && fn <= OPS.endPath) && // Path operator
++this._numInvalidPathOPS > MAX_INVALID_PATH_OPS) {
throw new FormatError(`Invalid ${partialMsg}`);
}
// If we receive too few arguments, it's not possible to execute
// the command, hence we skip the command.
warn('Skipping command ' + fn + ': expected ' + numArgs +
' args, but received ' + argsLength + ' args.');
warn(`Skipping ${partialMsg}`);
if (args !== null) {
args.length = 0;
}
continue;
}
} else if (argsLength > numArgs) {
info('Command ' + fn + ': expected [0,' + numArgs +
'] args, but received ' + argsLength + ' args.');
info(`Command ${cmd}: expected [0, ${numArgs}] args, ` +
`but received ${argsLength} args.`);
}
// TODO figure out how to type-check vararg functions

1
test/pdfs/bug1443140.pdf.link Normal file
View File

@ -0,0 +1 @@
https://web.archive.org/web/20180324105403/https://engineering.purdue.edu/~chengkok/papers/2005/p507-li.pdf

12
test/test_manifest.json
View File

@ -126,8 +126,7 @@
"file": "pdfs/issue2391-1.pdf",
"md5": "25ae9cb959612e7b343b55da63af2716",
"rounds": 1,
"lastPage": 1,
"type": "load"
"type": "eq"
},
{ "id": "issue2391-2",
"file": "pdfs/issue2391-2.pdf",
@ -135,6 +134,15 @@
"rounds": 1,
"type": "eq"
},
{ "id": "bug1443140",
"file": "pdfs/bug1443140.pdf",
"md5": "8f9347b0d5620537850b24b8385b0982",
"rounds": 1,
"link": true,
"firstPage": 4,
"lastPage": 4,
"type": "eq"
},
{ "id": "issue2531",
"file": "pdfs/issue2531.pdf",
"md5": "c58e6642d8a6e2ddd5e07a543ef8f30d",

28
test/unit/evaluator_spec.js
View File

@ -216,6 +216,34 @@ describe('evaluator', function() {
done();
});
});
it('should error if (many) path operators have too few arguments ' +
'(bug 1443140)', function(done) {
const NUM_INVALID_OPS = 25;
const tempArr = new Array(NUM_INVALID_OPS + 1);
// Non-path operators, should be ignored.
const invalidMoveText = tempArr.join('10 Td\n');
const moveTextStream = new StringStream(invalidMoveText);
runOperatorListCheck(partialEvaluator, moveTextStream,
new ResourcesMock(), function(result) {
expect(result.argsArray).toEqual([]);
expect(result.fnArray).toEqual([]);
done();
});
// Path operators, should throw error.
const invalidLineTo = tempArr.join('20 l\n');
const lineToStream = new StringStream(invalidLineTo);
runOperatorListCheck(partialEvaluator, lineToStream, new ResourcesMock(),
function(error) {
expect(error instanceof FormatError).toEqual(true);
expect(error.message).toEqual(
'Invalid command l: expected 2 args, but received 1 args.');
done();
});
});
it('should close opened saves', function(done) {
var stream = new StringStream('qq');
runOperatorListCheck(partialEvaluator, stream, new ResourcesMock(),