iolog_open.c

/*
 * SPDX-License-Identifier: ISC
 *
 * Copyright (c) 2009-2021 Todd C. Miller <[email protected]>
 *
 * 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 <config.h>

#include <stdio.h>
#include <stdlib.h>
#ifdef HAVE_STDBOOL_H
# include <stdbool.h>
#else
# include <compat/stdbool.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>

#include <sudo_compat.h>
#include <sudo_debug.h>
#include <sudo_iolog.h>
#include <sudo_util.h>

static unsigned char const gzip_magic[2] = {0x1f, 0x8b};

/*
 * Open the specified I/O log file and store in iol.
 * Stores the open file handle which has the close-on-exec flag set.
 * Also locks the file if iofd is IOFD_TIMING and mode is writable.
 * The "r+" and "w+" modes are not supported for compressed logs
 * so the "+" will be stripped before calling gzdopen().
 */
bool
iolog_open(struct iolog_file *iol, int dfd, int iofd, const char *mode)
{
    int flags;
    const char *file;
    bool lockit = false;
    unsigned char magic[2];
    const uid_t iolog_uid = iolog_get_uid();
    const gid_t iolog_gid = iolog_get_gid();
    debug_decl(iolog_open, SUDO_DEBUG_UTIL);

    if (mode[0] == 'r') {
	flags = mode[1] == '+' ? O_RDWR : O_RDONLY;
    } else if (mode[0] == 'w') {
	flags = O_CREAT|O_TRUNC;
	flags |= mode[1] == '+' ? O_RDWR : O_WRONLY;
    } else {
	sudo_debug_printf(SUDO_DEBUG_ERROR,
	    "%s: invalid I/O mode %s", __func__, mode);
	debug_return_bool(false);
    }
    if ((file = iolog_fd_to_name(iofd)) == NULL) {
	sudo_debug_printf(SUDO_DEBUG_ERROR,
	    "%s: invalid iofd %d", __func__, iofd);
	debug_return_bool(false);
    }

    /* Lock the timing file if opening for writing. */
    if (iofd == IOFD_TIMING && (mode[0] == 'w' || mode[1] == '+')) {
	lockit = true;
    }

    iol->writable = false;
    iol->compressed = false;
    iol->locked = false;
    if (iol->enabled) {
	int fd = iolog_openat(dfd, file, flags);
	if (lockit && fd != -1) {
	    if (sudo_lock_file(fd, SUDO_TLOCK)) {
		iol->locked = true;
	    } else {
		sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
		    "%s: unable to lock %s", __func__, file);
		close(fd);
		fd = -1;
	    }
	}
	if (fd != -1) {
	    if (*mode == 'w') {
		if (fchown(fd, iolog_uid, iolog_gid) != 0) {
		    sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_ERRNO,
			"%s: unable to fchown %d:%d %s", __func__,
			(int)iolog_uid, (int)iolog_gid, file);
		}
		iol->compressed = iolog_get_compress();
	    } else {
		/* check for gzip magic number */
		if (pread(fd, magic, sizeof(magic), 0) == ssizeof(magic)) {
		    if (magic[0] == gzip_magic[0] && magic[1] == gzip_magic[1])
			iol->compressed = true;
		}
	    }
	    /*
	     * Compressed logs don't support random access, gzdopen() will
	     * fail for mode "r+".  Caller must check the compressed flag.
	     */
	    if (iol->compressed)
		mode = *mode == 'r' ? "r" : "w";
	    if (fcntl(fd, F_SETFD, FD_CLOEXEC) != -1) {
#ifdef HAVE_ZLIB_H
		if (iol->compressed)
		    iol->fd.g = gzdopen(fd, mode);
		else
#endif
		    iol->fd.f = fdopen(fd, mode);
	    }
	    if (iol->fd.v != NULL) {
		switch ((flags & O_ACCMODE)) {
		case O_WRONLY:
		case O_RDWR:
		    iol->writable = true;
		    break;
		}
	    } else {
		int save_errno = errno;
		close(fd);
		errno = save_errno;
		fd = -1;
	    }
	}
	if (fd == -1) {
	    iol->enabled = false;
	    debug_return_bool(false);
	}
    } else {
	if (*mode == 'w') {
	    /* Remove old log file in case we recycled sequence numbers. */
	    (void)unlinkat(dfd, file, 0);
	}
    }
    debug_return_bool(true);
}