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buffer: do not affect memory after target for utf16 write #26432

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buffer: do not affect memory after target for utf16 write #26432

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11 changes: 6 additions & 5 deletions src/string_bytes.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -287,18 +287,19 @@ size_t StringBytes::WriteUCS2(Isolate* isolate,
CHECK_EQ(reinterpret_cast<uintptr_t>(aligned_dst) % sizeof(*dst), 0);

// Write all but the last char
max_chars = std::min(max_chars, static_cast<size_t>(str->Length()));
if (max_chars == 0) return 0;
nchars = str->Write(isolate, aligned_dst, 0, max_chars - 1, flags);
CHECK_EQ(nchars, max_chars - 1);

// Shift everything to unaligned-left
memmove(dst, aligned_dst, nchars * sizeof(*dst));

// One more char to be written
uint16_t last;
if (nchars == max_chars - 1 &&
str->Write(isolate, &last, nchars, 1, flags) != 0) {
memcpy(buf + nchars * sizeof(*dst), &last, sizeof(last));
nchars++;
}
CHECK_EQ(str->Write(isolate, &last, nchars, 1, flags), 1);
memcpy(buf + nchars * sizeof(*dst), &last, sizeof(last));
nchars++;

*chars_written = nchars;
return nchars * sizeof(*dst);
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8 changes: 8 additions & 0 deletions test/parallel/test-buffer-write.js
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Expand Up @@ -91,3 +91,11 @@ assert.strictEqual(Buffer.compare(z, Buffer.alloc(4, 0)), 0);
// Large overrun could corrupt the process
assert.strictEqual(Buffer.alloc(4)
.write('ыыыыыы'.repeat(100), 3, 'utf16le'), 0);

{
// .write() does not affect the byte after the written-to slice of the Buffer.
// Refs: https://github.com/nodejs/node/issues/26422
const buf = Buffer.alloc(8);
assert.strictEqual(buf.write('ыы', 1, 'utf16le'), 4);
assert.deepStrictEqual([...buf], [0, 0x4b, 0x04, 0x4b, 0x04, 0, 0, 0]);
}