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In io_write_buf() adjust the calculation of the multiplex message size
so that the loop works even for buffers bigger than 0xffffff. The code
does not produce such big buffers but better make the code correct.
Reported by Blago Dachev (blago (at) dachev (dot) com)
OK benno@

/*	$OpenBSD: io.c,v 1.21 2021/12/28 11:59:48 claudio Exp $ */
/*
 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <sys/stat.h>

#include <assert.h>
#include <endian.h>
#include <errno.h>
#include <poll.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

/*
 * A non-blocking check to see whether there's POLLIN data in fd.
 * Returns <0 on failure, 0 if there's no data, >0 if there is.
 */
int
io_read_check(int fd)
{
	struct pollfd	pfd;

	pfd.fd = fd;
	pfd.events = POLLIN;

	if (poll(&pfd, 1, 0) == -1) {
		ERR("poll");
		return -1;
	}
	return (pfd.revents & POLLIN);
}

/*
 * Write buffer to non-blocking descriptor.
 * Returns zero on failure, non-zero on success (zero or more bytes).
 * On success, fills in "sz" with the amount written.
 */
static int
io_write_nonblocking(int fd, const void *buf, size_t bsz,
    size_t *sz)
{
	struct pollfd	pfd;
	ssize_t		wsz;
	int		c;

	*sz = 0;

	if (bsz == 0)
		return 1;

	pfd.fd = fd;
	pfd.events = POLLOUT;

	/* Poll and check for all possible errors. */

	if ((c = poll(&pfd, 1, poll_timeout)) == -1) {
		ERR("poll");
		return 0;
	} else if (c == 0) {
		ERRX("poll: timeout");
		return 0;
	} else if ((pfd.revents & (POLLERR|POLLNVAL))) {
		ERRX("poll: bad fd");
		return 0;
	} else if ((pfd.revents & POLLHUP)) {
		ERRX("poll: hangup");
		return 0;
	} else if (!(pfd.revents & POLLOUT)) {
		ERRX("poll: unknown event");
		return 0;
	}

	/* Now the non-blocking write. */

	if ((wsz = write(fd, buf, bsz)) == -1) {
		ERR("write");
		return 0;
	}

	*sz = wsz;
	return 1;
}

/*
 * Blocking write of the full size of the buffer.
 * Returns 0 on failure, non-zero on success (all bytes written).
 */
static int
io_write_blocking(int fd, const void *buf, size_t sz)
{
	size_t		wsz;
	int		c;

	while (sz > 0) {
		c = io_write_nonblocking(fd, buf, sz, &wsz);
		if (!c) {
			ERRX1("io_write_nonblocking");
			return 0;
		} else if (wsz == 0) {
			ERRX("io_write_nonblocking: short write");
			return 0;
		}
		buf += wsz;
		sz -= wsz;
	}

	return 1;
}

/*
 * Write "buf" of size "sz" to non-blocking descriptor.
 * Returns zero on failure, non-zero on success (all bytes written to
 * the descriptor).
 */
int
io_write_buf(struct sess *sess, int fd, const void *buf, size_t sz)
{
	int32_t	 tag, tagbuf;
	size_t	 wsz;
	int	 c;

	if (!sess->mplex_writes) {
		c = io_write_blocking(fd, buf, sz);
		sess->total_write += sz;
		return c;
	}

	while (sz > 0) {
		wsz = (sz < 0xFFFFFF) ? sz : 0xFFFFFF;
		tag = (7 << 24) + wsz;
		tagbuf = htole32(tag);
		if (!io_write_blocking(fd, &tagbuf, sizeof(tagbuf))) {
			ERRX1("io_write_blocking");
			return 0;
		}
		if (!io_write_blocking(fd, buf, wsz)) {
			ERRX1("io_write_blocking");
			return 0;
		}
		sess->total_write += wsz;
		sz -= wsz;
		buf += wsz;
	}

	return 1;
}

/*
 * Write "line" (NUL-terminated) followed by a newline.
 * Returns zero on failure, non-zero on succcess.
 */
int
io_write_line(struct sess *sess, int fd, const char *line)
{

	if (!io_write_buf(sess, fd, line, strlen(line)))
		ERRX1("io_write_buf");
	else if (!io_write_byte(sess, fd, '\n'))
		ERRX1("io_write_byte");
	else
		return 1;

	return 0;
}

/*
 * Read buffer from non-blocking descriptor.
 * Returns zero on failure, non-zero on success (zero or more bytes).
 */
static int
io_read_nonblocking(int fd, void *buf, size_t bsz, size_t *sz)
{
	struct pollfd	pfd;
	ssize_t		rsz;
	int		c;

	*sz = 0;

	if (bsz == 0)
		return 1;

	pfd.fd = fd;
	pfd.events = POLLIN;

	/* Poll and check for all possible errors. */

	if ((c = poll(&pfd, 1, poll_timeout)) == -1) {
		ERR("poll");
		return 0;
	} else if (c == 0) {
		ERRX("poll: timeout");
		return 0;
	} else if ((pfd.revents & (POLLERR|POLLNVAL))) {
		ERRX("poll: bad fd");
		return 0;
	} else if (!(pfd.revents & (POLLIN|POLLHUP))) {
		ERRX("poll: unknown event");
		return 0;
	}

	/* Now the non-blocking read, checking for EOF. */

	if ((rsz = read(fd, buf, bsz)) == -1) {
		ERR("read");
		return 0;
	} else if (rsz == 0) {
		ERRX("unexpected end of file");
		return 0;
	}

	*sz = rsz;
	return 1;
}

/*
 * Blocking read of the full size of the buffer.
 * This can be called from either the error type message or a regular
 * message---or for that matter, multiplexed or not.
 * Returns 0 on failure, non-zero on success (all bytes read).
 */
static int
io_read_blocking(int fd, void *buf, size_t sz)
{
	size_t	 rsz;
	int	 c;

	while (sz > 0) {
		c = io_read_nonblocking(fd, buf, sz, &rsz);
		if (!c) {
			ERRX1("io_read_nonblocking");
			return 0;
		} else if (rsz == 0) {
			ERRX("io_read_nonblocking: short read");
			return 0;
		}
		buf += rsz;
		sz -= rsz;
	}

	return 1;
}

/*
 * When we do a lot of writes in a row (such as when the sender emits
 * the file list), the server might be sending us multiplexed log
 * messages.
 * If it sends too many, it clogs the socket.
 * This function looks into the read buffer and clears out any log
 * messages pending.
 * If called when there are valid data reads available, this function
 * does nothing.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_flush(struct sess *sess, int fd)
{
	int32_t	 tagbuf, tag;
	char	 mpbuf[1024];

	if (sess->mplex_read_remain)
		return 1;

	/*
	 * First, read the 4-byte multiplex tag.
	 * The first byte is the tag identifier (7 for normal
	 * data, !7 for out-of-band data), the last three are
	 * for the remaining data size.
	 */

	if (!io_read_blocking(fd, &tagbuf, sizeof(tagbuf))) {
		ERRX1("io_read_blocking");
		return 0;
	}
	tag = le32toh(tagbuf);
	sess->mplex_read_remain = tag & 0xFFFFFF;
	tag >>= 24;
	if (tag == 7)
		return 1;

	tag -= 7;

	if (sess->mplex_read_remain > sizeof(mpbuf)) {
		ERRX("multiplex buffer overflow");
		return 0;
	} else if (sess->mplex_read_remain == 0)
		return 1;

	if (!io_read_blocking(fd, mpbuf, sess->mplex_read_remain)) {
		ERRX1("io_read_blocking");
		return 0;
	}
	if (mpbuf[sess->mplex_read_remain - 1] == '\n')
		mpbuf[--sess->mplex_read_remain] = '\0';

	/*
	 * Always print the server's messages, as the server
	 * will control its own log levelling.
	 */

	LOG0("%.*s", (int)sess->mplex_read_remain, mpbuf);
	sess->mplex_read_remain = 0;

	/*
	 * I only know that a tag of one means an error.
	 * This means that we should exit.
	 */

	if (tag == 1) {
		ERRX1("error from remote host");
		return 0;
	}
	return 1;
}

/*
 * Read buffer from non-blocking descriptor, possibly in multiplex read
 * mode.
 * Returns zero on failure, non-zero on success (all bytes read from
 * the descriptor).
 */
int
io_read_buf(struct sess *sess, int fd, void *buf, size_t sz)
{
	size_t	 rsz;
	int	 c;

	/* If we're not multiplexing, read directly. */

	if (!sess->mplex_reads) {
		assert(sess->mplex_read_remain == 0);
		c = io_read_blocking(fd, buf, sz);
		sess->total_read += sz;
		return c;
	}

	while (sz > 0) {
		/*
		 * First, check to see if we have any regular data
		 * hanging around waiting to be read.
		 * If so, read the lesser of that data and whatever
		 * amount we currently want.
		 */

		if (sess->mplex_read_remain) {
			rsz = sess->mplex_read_remain < sz ?
				sess->mplex_read_remain : sz;
			if (!io_read_blocking(fd, buf, rsz)) {
				ERRX1("io_read_blocking");
				return 0;
			}
			sz -= rsz;
			sess->mplex_read_remain -= rsz;
			buf += rsz;
			sess->total_read += rsz;
			continue;
		}

		assert(sess->mplex_read_remain == 0);
		if (!io_read_flush(sess, fd)) {
			ERRX1("io_read_flush");
			return 0;
		}
	}

	return 1;
}

/*
 * Like io_write_buf(), but for a long (which is a composite type).
 * Returns zero on failure, non-zero on success.
 */
int
io_write_ulong(struct sess *sess, int fd, uint64_t val)
{
	uint64_t	nv;
	int64_t		sval = (int64_t)val;

	/* Short-circuit: send as an integer if possible. */

	if (sval <= INT32_MAX && sval >= 0) {
		if (!io_write_int(sess, fd, (int32_t)val)) {
			ERRX1("io_write_int");
			return 0;
		}
		return 1;
	}

	/* Otherwise, pad with -1 32-bit, then send 64-bit. */

	nv = htole64(val);

	if (!io_write_int(sess, fd, -1))
		ERRX1("io_write_int");
	else if (!io_write_buf(sess, fd, &nv, sizeof(int64_t)))
		ERRX1("io_write_buf");
	else
		return 1;

	return 0;
}

int
io_write_long(struct sess *sess, int fd, int64_t val)
{
	return io_write_ulong(sess, fd, (uint64_t)val);
}

/*
 * Like io_write_buf(), but for an unsigned integer.
 * Returns zero on failure, non-zero on success.
 */
int
io_write_uint(struct sess *sess, int fd, uint32_t val)
{
	uint32_t	nv;

	nv = htole32(val);

	if (!io_write_buf(sess, fd, &nv, sizeof(uint32_t))) {
		ERRX1("io_write_buf");
		return 0;
	}
	return 1;
}

/*
 * Like io_write_buf(), but for an integer.
 * Returns zero on failure, non-zero on success.
 */
int
io_write_int(struct sess *sess, int fd, int32_t val)
{
	return io_write_uint(sess, fd, (uint32_t)val);
}

/*
 * A simple assertion-protected memory copy from th einput "val" or size
 * "valsz" into our buffer "buf", full size "buflen", position "bufpos".
 * Increases our "bufpos" appropriately.
 * This has no return value, but will assert() if the size of the buffer
 * is insufficient for the new data.
 */
void
io_buffer_buf(void *buf, size_t *bufpos, size_t buflen, const void *val,
    size_t valsz)
{

	assert(*bufpos + valsz <= buflen);
	memcpy(buf + *bufpos, val, valsz);
	*bufpos += valsz;
}

/*
 * Like io_buffer_buf(), but also accomodating for multiplexing codes.
 * This should NEVER be passed to io_write_buf(), but instead passed
 * directly to a write operation.
 */
void
io_lowbuffer_buf(struct sess *sess, void *buf,
	size_t *bufpos, size_t buflen, const void *val, size_t valsz)
{
	int32_t	tagbuf;

	if (valsz == 0)
		return;

	if (!sess->mplex_writes) {
		io_buffer_buf(buf, bufpos, buflen, val, valsz);
		return;
	}

	assert(*bufpos + valsz + sizeof(int32_t) <= buflen);
	assert(valsz == (valsz & 0xFFFFFF));
	tagbuf = htole32((7 << 24) + valsz);

	io_buffer_int(buf, bufpos, buflen, tagbuf);
	io_buffer_buf(buf, bufpos, buflen, val, valsz);
}

/*
 * Allocate the space needed for io_lowbuffer_buf() and friends.
 * This should be called for *each* lowbuffer operation, so:
 *   io_lowbuffer_alloc(... sizeof(int32_t));
 *   io_lowbuffer_int(...);
 *   io_lowbuffer_alloc(... sizeof(int32_t));
 *   io_lowbuffer_int(...);
 * And not sizeof(int32_t) * 2 or whatnot.
 * Returns zero on failure, non-zero on succes.
 */
int
io_lowbuffer_alloc(struct sess *sess, void **buf,
	size_t *bufsz, size_t *bufmax, size_t sz)
{
	void	*pp;
	size_t	 extra;

	extra = sess->mplex_writes ? sizeof(int32_t) : 0;

	if (*bufsz + sz + extra > *bufmax) {
		pp = realloc(*buf, *bufsz + sz + extra);
		if (pp == NULL) {
			ERR("realloc");
			return 0;
		}
		*buf = pp;
		*bufmax = *bufsz + sz + extra;
	}
	*bufsz += sz + extra;
	return 1;
}

/*
 * Like io_lowbuffer_buf(), but for a single integer.
 */
void
io_lowbuffer_int(struct sess *sess, void *buf,
	size_t *bufpos, size_t buflen, int32_t val)
{
	int32_t	nv = htole32(val);

	io_lowbuffer_buf(sess, buf, bufpos, buflen, &nv, sizeof(int32_t));
}

/*
 * Like io_buffer_buf(), but for a single integer.
 */
void
io_buffer_int(void *buf, size_t *bufpos, size_t buflen, int32_t val)
{
	int32_t	nv = htole32(val);

	io_buffer_buf(buf, bufpos, buflen, &nv, sizeof(int32_t));
}

/*
 * Like io_read_buf(), but for a long >=0.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_long(struct sess *sess, int fd, int64_t *val)
{
	uint64_t	uoval;

	if (!io_read_ulong(sess, fd, &uoval)) {
		ERRX1("io_read_long");
		return 0;
	}
	*val = (int64_t)uoval;
	if (*val < 0) {
		ERRX1("io_read_long negative");
		return 0;
	}
	return 1;
}

/*
 * Like io_read_buf(), but for a long.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_ulong(struct sess *sess, int fd, uint64_t *val)
{
	uint64_t	 oval;
	int32_t		 sval;

	/* Start with the short-circuit: read as an int. */

	if (!io_read_int(sess, fd, &sval)) {
		ERRX1("io_read_int");
		return 0;
	} else if (sval != -1) {
		*val = (uint64_t)le32toh(sval);
		return 1;
	}

	/* If the int is -1, read as 64 bits. */

	if (!io_read_buf(sess, fd, &oval, sizeof(uint64_t))) {
		ERRX1("io_read_buf");
		return 0;
	}

	*val = le64toh(oval);
	return 1;
}

/*
 * One thing we often need to do is read a size_t.
 * These are transmitted as int32_t, so make sure that the value
 * transmitted is not out of range.
 * FIXME: I assume that size_t can handle int32_t's max.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_size(struct sess *sess, int fd, size_t *val)
{
	int32_t	oval;

	if (!io_read_int(sess, fd, &oval)) {
		ERRX1("io_read_int");
		return 0;
	} else if (oval < 0) {
		ERRX("io_read_size: negative value");
		return 0;
	}

	*val = oval;
	return 1;
}

/*
 * Like io_read_buf(), but for an integer.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_uint(struct sess *sess, int fd, uint32_t *val)
{
	uint32_t	oval;

	if (!io_read_buf(sess, fd, &oval, sizeof(uint32_t))) {
		ERRX1("io_read_buf");
		return 0;
	}

	*val = le32toh(oval);
	return 1;
}

int
io_read_int(struct sess *sess, int fd, int32_t *val)
{
	return io_read_uint(sess, fd, (uint32_t *)val);
}

/*
 * Copies "valsz" from "buf", full size "bufsz" at position" bufpos",
 * into "val".
 * Calls assert() if the source doesn't have enough data.
 * Increases "bufpos" to the new position.
 */
void
io_unbuffer_buf(const void *buf, size_t *bufpos, size_t bufsz, void *val,
    size_t valsz)
{

	assert(*bufpos + valsz <= bufsz);
	memcpy(val, buf + *bufpos, valsz);
	*bufpos += valsz;
}

/*
 * Calls io_unbuffer_buf() and converts.
 */
void
io_unbuffer_int(const void *buf, size_t *bufpos, size_t bufsz, int32_t *val)
{
	int32_t	oval;

	io_unbuffer_buf(buf, bufpos, bufsz, &oval, sizeof(int32_t));
	*val = le32toh(oval);
}

/*
 * Calls io_unbuffer_buf() and converts.
 */
int
io_unbuffer_size(const void *buf, size_t *bufpos, size_t bufsz, size_t *val)
{
	int32_t	oval;

	io_unbuffer_int(buf, bufpos, bufsz, &oval);
	if (oval < 0) {
		ERRX("io_unbuffer_size: negative value");
		return 0;
	}
	*val = oval;
	return 1;
}

/*
 * Like io_read_buf(), but for a single byte >=0.
 * Returns zero on failure, non-zero on success.
 */
int
io_read_byte(struct sess *sess, int fd, uint8_t *val)
{

	if (!io_read_buf(sess, fd, val, sizeof(uint8_t))) {
		ERRX1("io_read_buf");
		return 0;
	}
	return 1;
}

/*
 * Like io_write_buf(), but for a single byte.
 * Returns zero on failure, non-zero on success.
 */
int
io_write_byte(struct sess *sess, int fd, uint8_t val)
{

	if (!io_write_buf(sess, fd, &val, sizeof(uint8_t))) {
		ERRX1("io_write_buf");
		return 0;
	}
	return 1;
}