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std.compress.xz: Avoid possible integer overflow in a few places #14521

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std.compress.xz: Avoid possible integer overflow in a few places #14521

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2 changes: 1 addition & 1 deletion lib/std/compress/xz.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -118,7 +118,7 @@ pub fn Decompress(comptime ReaderType: type) type {
var hasher = std.compress.hashedReader(self.in_reader, Crc32.init());
const hashed_reader = hasher.reader();

const backward_size = (try hashed_reader.readIntLittle(u32) + 1) * 4;
const backward_size = (@as(u64, try hashed_reader.readIntLittle(u32)) + 1) * 4;
if (backward_size != index_size)
return error.CorruptInput;

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4 changes: 2 additions & 2 deletions lib/std/compress/xz/block.zig
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Expand Up @@ -98,7 +98,7 @@ pub fn Decoder(comptime ReaderType: type) type {
var header_hasher = std.compress.hashedReader(block_reader, Crc32.init());
const header_reader = header_hasher.reader();

const header_size = try header_reader.readByte() * 4;
const header_size = @as(u64, try header_reader.readByte()) * 4;
if (header_size == 0)
return error.EndOfStreamWithNoError;

Expand Down Expand Up @@ -217,7 +217,7 @@ pub fn Decoder(comptime ReaderType: type) type {
if (status == 1)
try self.accum.reset(self.allocator);

const size = try packed_reader.readIntBig(u16) + 1;
const size = @as(u17, try packed_reader.readIntBig(u16)) + 1;
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Note that this will be superseded by/conflict with #14518 (comment)

Let me know if it'd be better to defer this fix to that PR

try self.accum.ensureUnusedCapacity(self.allocator, size);

var i: usize = 0;
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20 changes: 20 additions & 0 deletions lib/std/compress/xz/test.zig
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Expand Up @@ -78,3 +78,23 @@ test "unsupported" {
);
}
}

fn testDontPanic(data: []const u8) !void {
const buf = decompress(data) catch |err| switch (err) {
error.OutOfMemory => |e| return e,
else => return,
};
defer testing.allocator.free(buf);
}

test "size fields: integer overflow avoidance" {
// These cases were found via fuzz testing and each previously caused
// an integer overflow when decoding. We just want to ensure they no longer
// cause a panic
const header_size_overflow = "\xfd7zXZ\x00\x00\x01i\"\xde6z";
try testDontPanic(header_size_overflow);
const lzma2_chunk_size_overflow = "\xfd7zXZ\x00\x00\x01i\"\xde6\x02\x00!\x01\x08\x00\x00\x00\xd8\x0f#\x13\x01\xff\xff";
try testDontPanic(lzma2_chunk_size_overflow);
const backward_size_overflow = "\xfd7zXZ\x00\x00\x01i\"\xde6\x00\x00\x00\x00\x1c\xdfD!\x90B\x99\r\x01\x00\x00\xff\xff\x10\x00\x00\x00\x01DD\xff\xff\xff\x01";
try testDontPanic(backward_size_overflow);
}