Browse zlib specs (37 of 62)

Proofs / zlib / Sizes and memory

res_memory_inflate

Nor does decompression: at most the window plus the exact size of its state (7160 bytes).

spec
87 lines of C
with its headers
179 lines
status
Proved
37 of 62
On this page

The spec

The spec is the C program harness/res_memory_inflate.c, 87 lines, shown whole as it is in the repository at 37189f4. It includes harness/laws_common.h (40 lines) and harness/laws_session.h (52 lines). Its first comment states the property in full, with every bound.

C
// Law res_memory_inflate: Counted through the zalloc and zfree it is given, inflate never holds more than zconf.h's
// (1 << w) bytes plus 7160 bytes, the size of struct inflate_state on this platform (x86_64, LP64, CompCert), w the
// window bits (windowBits without the raw sign or the 16 or 32 of gzip and detection, 15 for 0), for inflateInit2 with
// any windowBits in zlib.h's ranges and any number of inflate() calls on any input (any length the allocator provides)
// in any pieces below 2^32 bytes, each with any output space and any flush: inflateInit2 returns Z_OK, or Z_MEM_ERROR
// only when the zalloc has returned Z_NULL; inflate returns Z_MEM_ERROR only when the zalloc has returned Z_NULL; and
// after every call, the most it has held at any time is within that bound.
#include "laws_common.h"
#include "laws_session.h"

struct count {
	size_t now;
	size_t peak;
	int failed;
};
static voidpf counted_alloc(voidpf opaque, uInt items, uInt size) {
	struct count *count = opaque;
	size_t bytes = (size_t) items * size;
	size_t *block = malloc(sizeof (size_t) + bytes);
	if (block == NULL) {
		count->failed = 1;
		return Z_NULL;
	}
	block[0] = bytes;
	count->now += bytes;
	if (count->now > count->peak)
		count->peak = count->now;
	return block + 1;
}
static void counted_free(voidpf opaque, voidpf address) {
	struct count *count = opaque;
	size_t *block = (size_t *) address - 1;
	count->now -= block[0];
	free(block);
}
static void counted_stream(z_stream *strm, struct count *count) {
	count->now = 0;
	count->peak = 0;
	count->failed = 0;
	strm->zalloc = counted_alloc;
	strm->zfree = counted_free;
	strm->opaque = count;
	set_buffer(strm, Z_NULL, 0, Z_NULL, 0);
}

int main(void) {
	int window_bits = (int) nondet_u32();
	gp_assume(inflate_window_ok(window_bits));
	size_t input_len = upto(PTRDIFF_MAX);
	unsigned char *input = alloc_any_bytes(input_len);
	if (input == NULL)
		return 0;
	struct count count;
	z_stream strm;
	counted_stream(&strm, &count);

	int code = inflateInit2(&strm, window_bits);

	// zlib.h, inflateInit2: "Z_MEM_ERROR if there was not enough memory"
	gp_assert(code == Z_OK || (code == Z_MEM_ERROR && count.failed));
	if (code != Z_OK)
		return 0;
	int w = window_bits & 15;
	if (window_bits < 0)
		w = -window_bits;
	if (w == 0)
		w = 15;
	size_t read = 0;
	do {
		size_t take = upto(clip(input_len - read));
		size_t room = nondet_u32();
		unsigned char *out = malloc(room);
		if (out == NULL)
			return 0;
		set_buffer(&strm, input + read, take, out, room);

		code = inflate(&strm, (int) nondet_u32());

		// zconf.h: "The memory requirements for inflate are (in bytes) 1 << windowBits that is, 32K for
		// windowBits=15 (default value) plus about 7 kilobytes for small objects."
		gp_assert(code != Z_MEM_ERROR || count.failed);
		gp_assert(count.peak <= (1ul << w) + 7160);
		read += take - strm.avail_in;
		free(out);
	} while (nondet_u8() != 0);
	return 0;
}
harness/laws_common.h, 40 lines
C
// laws_common.h: trivial helpers shared by the zlib laws (each law includes it once). No models, no algorithms.
#include <limits.h>
#include <stdlib.h>
#include "quickproof.h"
#include "zlib.h"
static size_t upto(size_t max) {
	size_t value = nondet_size();
	return value < max ? value : max;
}
static uInt clip(size_t n) { return n < UINT_MAX ? (uInt) n : UINT_MAX; }
static unsigned char *alloc_any_bytes(size_t n) {
	unsigned char *bytes = malloc(n);
	if (bytes != NULL)
		nondet_bytes(bytes, n);
	return bytes;
}
static unsigned char *copy_of(const unsigned char *source, size_t n) {
	unsigned char *copy = malloc(n);
	for (size_t i = 0; copy != NULL && i < n; i++)
		copy[i] = source[i];
	return copy;
}
static int bytes_eq(const unsigned char *a, const unsigned char *b, size_t n) {
	for (size_t i = 0; i < n; i++)
		if (a[i] != b[i])
			return 0;
	return 1;
}
static void set_buffer(z_stream *strm, unsigned char *in, size_t in_len, unsigned char *out, size_t out_len) {
	strm->next_in = in;
	strm->avail_in = (uInt) in_len;
	strm->next_out = out;
	strm->avail_out = (uInt) out_len;
}
static void new_stream(z_stream *strm) {
	strm->zalloc = Z_NULL;
	strm->zfree = Z_NULL;
	strm->opaque = Z_NULL;
	set_buffer(strm, Z_NULL, 0, Z_NULL, 0);
}
harness/laws_session.h, 52 lines
C
// laws_session.h: helpers of the laws that drive a z_stream, included after laws_common.h. No models, no algorithms.
static int deflate_params_ok(int level, int window_bits, int mem_level, int strategy) {
	// zlib.h, deflateInit2: level "Z_DEFAULT_COMPRESSION, or between 0 and 9"; memLevel 1..MAX_MEM_LEVEL (9,
	// zconf.h); strategy Z_DEFAULT_STRATEGY (0) .. Z_FIXED (4); windowBits 8..15, "-8..-15 for raw deflate", "Add 16
	// to windowBits to write a simple gzip header", but "For raw deflate or gzip encoding, a request for a 256-byte
	// window is rejected as invalid"
	int zlib_window = window_bits >= 8 && window_bits <= 15;
	int raw_window = window_bits >= -15 && window_bits <= -9;
	int gzip_window = window_bits >= 16 + 9 && window_bits <= 16 + 15;
	int valid = level >= -1 && level <= 9 && mem_level >= 1 && mem_level <= 9 && strategy >= 0 && strategy <= Z_FIXED;
	return valid && (zlib_window || raw_window || gzip_window);
}
static int inflate_window_ok(int window_bits) {
	// zlib.h, inflateInit2: windowBits "should be in the range 8..15", "can also be zero to request that inflate
	// use the window size in the zlib header", "can also be -8..-15 for raw inflate", "Add 32 to windowBits to
	// enable zlib and gzip decoding with automatic header detection, or add 16 to decode only the gzip format"
	int low = window_bits & 15;
	int raw = window_bits >= -15 && window_bits <= -8;
	int wrapped = window_bits >= 0 && window_bits < 48 && (low == 0 || low >= 8);
	return raw || wrapped;
}
struct position {
	unsigned char *next_in;
	uInt avail_in;
	unsigned char *next_out;
	uInt avail_out;
	uLong total_in;
	uLong total_out;
};
static void position_of(z_stream *strm, struct position *at) {
	at->next_in = strm->next_in;
	at->avail_in = strm->avail_in;
	at->next_out = strm->next_out;
	at->avail_out = strm->avail_out;
	at->total_in = strm->total_in;
	at->total_out = strm->total_out;
}
static int unmoved(z_stream *strm, struct position *at) {
	int in = strm->next_in == at->next_in && strm->avail_in == at->avail_in && strm->total_in == at->total_in;
	int out = strm->next_out == at->next_out && strm->avail_out == at->avail_out && strm->total_out == at->total_out;
	return in && out;
}
static int accounted(z_stream *strm, struct position *at) {
	int in = strm->avail_in <= at->avail_in && strm->next_in + strm->avail_in == at->next_in + at->avail_in;
	int out = strm->avail_out <= at->avail_out && strm->next_out + strm->avail_out == at->next_out + at->avail_out;
	return in && out;
}
static int counted(z_stream *strm, struct position *at) {
	int in = strm->total_in == at->total_in + (at->avail_in - strm->avail_in);
	int out = strm->total_out == at->total_out + (at->avail_out - strm->avail_out);
	return in && out;
}

The theorem

QuickProof generated this statement from the spec, in src/contracts/res_memory_inflate.v:

Rocq
Theorem res_memory_inflate : harness_safe whole_prog.

src/contracts/laws.v states it on the spec's own program, whole_prog (the spec linked with the code under test), with its proof:

Rocq
Theorem res_memory_inflate : harness_safe Zlib.contracts.res_memory_inflate.whole_prog.
Proof. exact (proj1 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 Zlib.contracts.suite.suite)))))))))))))))))))))). Qed.

Read as a statement about runs, it says that no run of the program has undefined behaviour or a failing check, for every value the spec can draw. That reading rests on VST's adequacy theorem, which is not yet instantiated in Rocq (formerly Coq) for QuickProof's environment.

The C files (units) its program links
  • adler32.c
  • crc32.c
  • inflate.c
  • inffast.c
  • inftrees.c
  • zutil.c
  • quickproof/libc/libc.c

What it leaves out

  • What the first comment of the spec excludes, and its bounds.
  • Like every spec of this proof: termination (a run that never returns is not a counterexample), and binaries built by a compiler (the theorem is about the code as CompCert defines C for x86_64, LP64), one thread.
  • Where zlib reports Z_MEM_ERROR, most specs end the run and claim nothing about it; the first comment of the spec says so.
  • The edits to zlib's code, listed in the repository, are tested, not proved.

The summary page says what the proof as a whole covers.

How it was proved

AI agents wrote the proof, and Rocq checks it. qp verify passes on this repository: this statement is the one generated from the spec at the contract commit, and its proof uses only Rocq's standard axioms and VST's abstract malloc library.