From f537377957f0f754fcc228c1a9fef40503812405 Mon Sep 17 00:00:00 2001 From: Justin Ridgewell Date: Fri, 24 Jan 2020 02:49:41 -0500 Subject: [PATCH] process: fix two overflow cases in SourceMap VLQ decoding These both have to do with extremely large numbers, so it's unlikely to cause a problem in practice. Still, correctness. First, encoding `-2147483648` in VLQ returns the value `"B"`. When decoding, we get the value `1` after reading the base64. We then check if the first bit is set (it is) to see if we should negate it, then we shift all bits right once. Now, `value` will be `0` and `negate` will be `true`. So, we'd return `-0`. Which is a bug! `-0` isn't `-2147483648`, and we've broken a round trip. Second, encoding any number with the 31st bit set, we'd return the opposite sign. Let's use `1073741824`. Encoding, we get `"ggggggC"`. When decoding, we get the value `-2147483648` after reading the base64. Notice, it's already negative (the 32nd bit is set, because the 31st was set and we shifted everything left once). We'd then check the first bit (it's not) and shift right. But we used `>>`, which does not shift the sign bit. We actually wanted `>>>`, which will. Because of that bug, we get back `-1073741824` instead of the positive `1073741824`. It's even worse if the 32nd and 31st bits are set, `-1610612736` becomes `536870912` after a round trip. I recently fixed the same two bugs in Closure Compiler: https://github.com/google/closure-compiler/commit/584418eb PR-URL: https://github.com/nodejs/node/pull/31490 Reviewed-By: Anna Henningsen Reviewed-By: Colin Ihrig Reviewed-By: Ben Coe Reviewed-By: David Carlier Reviewed-By: Rich Trott Reviewed-By: Gus Caplan --- lib/internal/source_map/source_map.js | 15 ++++++++-- test/parallel/test-source-map-api.js | 42 +++++++++++++++++++++++++++ 2 files changed, 55 insertions(+), 2 deletions(-) diff --git a/lib/internal/source_map/source_map.js b/lib/internal/source_map/source_map.js index 32fe43ac8f68cb..d66230ec37f312 100644 --- a/lib/internal/source_map/source_map.js +++ b/lib/internal/source_map/source_map.js @@ -303,8 +303,19 @@ function decodeVLQ(stringCharIterator) { // Fix the sign. const negative = result & 1; - result >>= 1; - return negative ? -result : result; + // Use unsigned right shift, so that the 32nd bit is properly shifted to the + // 31st, and the 32nd becomes unset. + result >>>= 1; + if (!negative) { + return result; + } + + // We need to OR here to ensure the 32nd bit (the sign bit in an Int32) is + // always set for negative numbers. If `result` were 1, (meaning `negate` is + // true and all other bits were zeros), `result` would now be 0. But -0 + // doesn't flip the 32nd bit as intended. All other numbers will successfully + // set the 32nd bit without issue, so doing this is a noop for them. + return -result | (1 << 31); } /** diff --git a/test/parallel/test-source-map-api.js b/test/parallel/test-source-map-api.js index e7704cf45cf68e..2bfbc08809e9a1 100644 --- a/test/parallel/test-source-map-api.js +++ b/test/parallel/test-source-map-api.js @@ -82,3 +82,45 @@ const { readFileSync } = require('fs'); assert.strictEqual(payload.sources[0], sourceMap.payload.sources[0]); assert.notStrictEqual(payload.sources, sourceMap.payload.sources); } + +// Test various known decodings to ensure decodeVLQ works correctly. +{ + function makeMinimalMap(column) { + return { + sources: ['test.js'], + // Mapping from the 0th line, 0th column of the output file to the 0th + // source file, 0th line, ${column}th column. + mappings: `AAA${column}`, + }; + } + const knownDecodings = { + 'A': 0, + 'B': -2147483648, + 'C': 1, + 'D': -1, + 'E': 2, + 'F': -2, + + // 2^31 - 1, maximum values + '+/////D': 2147483647, + '8/////D': 2147483646, + '6/////D': 2147483645, + '4/////D': 2147483644, + '2/////D': 2147483643, + '0/////D': 2147483642, + + // -2^31 + 1, minimum values + '//////D': -2147483647, + '9/////D': -2147483646, + '7/////D': -2147483645, + '5/////D': -2147483644, + '3/////D': -2147483643, + '1/////D': -2147483642, + }; + + for (const column in knownDecodings) { + const sourceMap = new SourceMap(makeMinimalMap(column)); + const { originalColumn } = sourceMap.findEntry(0, 0); + assert.strictEqual(originalColumn, knownDecodings[column]); + } +}