iolog_openat.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 <sys/stat.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 <unistd.h>

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

/*
 * Wrapper for openat(2) that sets umask and retries as iolog_uid/iolog_gid
 * if openat(2) returns EACCES.
 */
int
iolog_openat(int dfd, const char *path, int flags)
{
    const mode_t iolog_filemode = iolog_get_file_mode();
    const mode_t iolog_dirmode = iolog_get_dir_mode();
    mode_t omask = S_IRWXG|S_IRWXO;
    int fd;
    debug_decl(iolog_openat, SUDO_DEBUG_UTIL);

    if (ISSET(flags, O_CREAT)) {
	/* umask must not be more restrictive than the file modes. */
	omask = umask(ACCESSPERMS & ~(iolog_filemode|iolog_dirmode));
    }
    fd = openat(dfd, path, flags, iolog_filemode);
    if (fd == -1 && errno == EACCES) {
	/* Enable write bit if it is missing. */
	struct stat sb;
	if (fstatat(dfd, path, &sb, 0) == 0) {
	    mode_t write_bits = iolog_filemode & (S_IWUSR|S_IWGRP|S_IWOTH);
	    if ((sb.st_mode & write_bits) != write_bits) {
		if (fchmodat(dfd, path, iolog_filemode, 0) == 0)
		    fd = openat(dfd, path, flags, iolog_filemode);
	    }
	}
    }
    if (fd == -1 && errno == EACCES) {
	/* Try again as the I/O log owner (for NFS). */
	if (iolog_swapids(false)) {
	    fd = openat(dfd, path, flags, iolog_filemode);
	    if (!iolog_swapids(true)) {
		/* iolog_swapids() warns on error. */
		if (fd != -1) {
		    close(fd);
		    fd = -1;
		}
	    }
	}
    }
    if (ISSET(flags, O_CREAT))
	umask(omask);
    debug_return_int(fd);
}