programs: add regression test for overread check

Update #157

programs/test_overread.c

@@ -0,0 +1,95 @@
+/*
+ * test_overread.c
+ *
+ * Test that the decompressor doesn't produce an unbounded amount of output if
+ * it runs out of input, even when implicit zeroes appended to the input would
+ * continue producing output (as is the case when the input ends during a
+ * DYNAMIC_HUFFMAN block where a literal has an all-zeroes codeword).
+ *
+ * This is a regression test for commit 3f21ec9d6121 ("deflate_decompress: error
+ * out if overread count gets too large").
+ */
+
+#include "test_util.h"
+
+static void
+generate_test_input(struct output_bitstream *os)
+{
+	int i;
+
+	put_bits(os, 0, 1);	/* BFINAL: 0 */
+	put_bits(os, 2, 2);	/* BTYPE: DYNAMIC_HUFFMAN */
+
+	/*
+	 * Write the Huffman codes.
+	 *
+	 * Litlen code:
+	 *	litlensym_0   (0)		len=1 codeword=0
+	 *	litlensym_256 (end-of-block)	len=1 codeword=1
+	 * Offset code:
+	 *	offsetsym_0 (unused)		len=1 codeword=0
+	 *
+	 * Litlen and offset codeword lengths:
+	 *	[0]	 = 1	presym_1
+	 *	[1..255] = 0	presym_{18,18}
+	 *	[256]	 = 1	presym_1
+	 *	[257]	 = 1	presym_1
+	 *
+	 * Precode:
+	 *	presym_1	len=1 codeword=0
+	 *	presym_18	len=1 codeword=1
+	 */
+	put_bits(os, 0, 5);	/* num_litlen_syms: 0 + 257 */
+	put_bits(os, 0, 5);	/* num_offset_syms: 0 + 1 */
+	put_bits(os, 14, 4);	/* num_explicit_precode_lens: 14 + 4 */
+	/*
+	 * Precode codeword lengths: order is
+	 * [16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15]
+	 */
+	put_bits(os, 0, 3);		/* presym_16: len=0 */
+	put_bits(os, 0, 3);		/* presym_17: len=0 */
+	put_bits(os, 1, 3);		/* presym_18: len=1 */
+	for (i = 0; i < 14; i++)	/* presym_{0,...,14}: len=0 */
+		put_bits(os, 0, 3);
+	put_bits(os, 1, 3);		/* presym_1: len=1 */
+
+	/* Litlen and offset codeword lengths */
+	put_bits(os, 0, 1);		/* presym_1 */
+	put_bits(os, 1, 1);		/* presym_18 ... */
+	put_bits(os, 117, 7);		/* ... 11 + 117 zeroes */
+	put_bits(os, 1, 1);		/* presym_18 ... */
+	put_bits(os, 116, 7);		/* ... 11 + 116 zeroes */
+	put_bits(os, 0, 1);		/* presym_1 */
+	put_bits(os, 0, 1);		/* presym_1 */
+
+	/* Implicit zeroes would generate endless literals from here. */
+
+	ASSERT(flush_bits(os));
+}
+
+int
+tmain(int argc, tchar *argv[])
+{
+	u8 cdata[16];
+	u8 udata[256];
+	struct output_bitstream os =
+		{ .next = cdata, .end = cdata + sizeof(cdata) };
+	struct libdeflate_decompressor *d;
+	enum libdeflate_result res;
+	size_t actual_out_nbytes;
+
+	begin_program(argv);
+
+	generate_test_input(&os);
+	d = libdeflate_alloc_decompressor();
+	ASSERT(d != NULL);
+
+	res = libdeflate_deflate_decompress(d, cdata, os.next - cdata,
+					    udata, sizeof(udata),
+					    &actual_out_nbytes);
+	/* Before the fix, the result was LIBDEFLATE_INSUFFICIENT_SPACE here. */
+	ASSERT(res == LIBDEFLATE_BAD_DATA);
+
+	libdeflate_free_decompressor(d);
+	return 0;
+}