annotate contrib/fuzz/mpatch.cc @ 49275:c6a3243567b6

chg: replace mercurial.util.recvfds() by simpler pure Python implementation

On Python 3, we have socket.socket.recvmsg(). This makes it possible to receive
FDs in pure Python code. The new code behaves like the previous
implementations, except that it’s more strict about the format of the ancillary
data. This works because we know in which format the FDs are passed.

Because the code is (and always has been) specific to chg (payload is 1 byte,
number of passed FDs is limited) and we now have only one implementation and
the code is very short, I decided to stop exposing a function in
mercurial.util.

Note on terminology: The SCM_RIGHTS mechanism is used to share open file
descriptions to another process over a socket. The sending side passes an array
of file descriptors and the receiving side receives an array of file
descriptors. The file descriptors are different in general on both sides but
refer to the same open file descriptions. The two terms are often conflated,
even in the official documentation. That’s why I used “FD” above, which could
mean both “file descriptor” and “file description”.

/*
 * mpatch.cc - fuzzer harness for mpatch.c
 *
 * Copyright 2018, Google Inc.
 *
 * This software may be used and distributed according to the terms of
 * the GNU General Public License, incorporated herein by reference.
 */
#include <iostream>
#include <memory>
#include <stdint.h>
#include <stdlib.h>
#include <vector>

#include "fuzzutil.h"

extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv)
{
	return 0;
}

// To avoid having too many OOMs from the fuzzer infrastructure, we'll
// skip patch application if the resulting fulltext would be bigger
// than 10MiB.
#define MAX_OUTPUT_SIZE 10485760

extern "C" {
#include "bitmanipulation.h"
#include "mpatch.h"

struct mpatchbin {
	std::unique_ptr<char[]> data;
	size_t len;
};

static mpatch_flist *getitem(void *vbins, ssize_t pos)
{
	std::vector<mpatchbin> *bins = (std::vector<mpatchbin> *)vbins;
	const mpatchbin &bin = bins->at(pos + 1);
	struct mpatch_flist *res;
	LOG(2) << "mpatch_decode " << bin.len << std::endl;
	if (mpatch_decode(bin.data.get(), bin.len, &res) < 0)
		return NULL;
	return res;
}

// input format:
// u8 number of inputs
// one u16 for each input, its length
// the inputs
int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
{
	if (!Size) {
		return 0;
	}
	// First byte of data is how many texts we expect, first text
	// being the base the rest being the deltas.
	ssize_t numtexts = Data[0];
	if (numtexts < 2) {
		// No point if we don't have at least a base text and a delta...
		return 0;
	}
	// Each text will be described by a byte for how long it
	// should be, so give up if we don't have enough.
	if ((Size - 1) < (numtexts * 2)) {
		return 0;
	}
	size_t consumed = 1 + (numtexts * 2);
	LOG(2) << "input contains " << Size << std::endl;
	LOG(2) << numtexts << " texts, consuming " << consumed << std::endl;
	std::vector<mpatchbin> bins;
	bins.reserve(numtexts);
	for (int i = 0; i < numtexts; ++i) {
		mpatchbin bin;
		size_t nthsize = getbeuint16((char *)Data + 1 + (2 * i));
		LOG(2) << "text " << i << " is " << nthsize << std::endl;
		char *start = (char *)Data + consumed;
		consumed += nthsize;
		if (consumed > Size) {
			LOG(2) << "ran out of data, consumed " << consumed
			       << " of " << Size << std::endl;
			return 0;
		}
		bin.len = nthsize;
		bin.data.reset(new char[nthsize]);
		memcpy(bin.data.get(), start, nthsize);
		bins.push_back(std::move(bin));
	}
	LOG(2) << "mpatch_flist" << std::endl;
	struct mpatch_flist *patch =
	    mpatch_fold(&bins, getitem, 0, numtexts - 1);
	if (!patch) {
		return 0;
	}
	LOG(2) << "mpatch_calcsize" << std::endl;
	ssize_t outlen = mpatch_calcsize(bins[0].len, patch);
	LOG(2) << "outlen " << outlen << std::endl;
	if (outlen < 0 || outlen > MAX_OUTPUT_SIZE) {
		goto cleanup;
	}
	{
		char *dest = (char *)malloc(outlen);
		LOG(2) << "expecting " << outlen << " total bytes at "
		       << (void *)dest << std::endl;
		mpatch_apply(dest, bins[0].data.get(), bins[0].len, patch);
		free(dest);
		LOG(1) << "applied a complete patch" << std::endl;
	}
cleanup:
	mpatch_lfree(patch);
	return 0;
}

} // extern "C"