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https://github.com/shadow-maint/shadow.git
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215 lines
6.5 KiB
C
215 lines
6.5 KiB
C
/*
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* SPDX-FileCopyrightText: 2013 Eric Biederman
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <config.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <strings.h>
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#include "alloc/calloc.h"
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#include "alloc/x/xmalloc.h"
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#include "atoi/a2i/a2u.h"
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#include "prototypes.h"
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#include "string/sprintf/stpeprintf.h"
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#include "idmapping.h"
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#if HAVE_SYS_CAPABILITY_H
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#include <sys/prctl.h>
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#include <sys/capability.h>
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#endif
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#include "shadowlog.h"
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#include "sizeof.h"
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struct map_range *
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get_map_ranges(int ranges, int argc, char **argv)
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{
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struct map_range *mappings, *m;
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if (ranges < 0 || argc < 0) {
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fprintf(log_get_logfd(), "%s: error calculating number of arguments\n", log_get_progname());
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return NULL;
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}
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if (ranges * 3 != argc) {
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fprintf(log_get_logfd(), "%s: ranges: %u is wrong for argc: %d\n", log_get_progname(), ranges, argc);
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return NULL;
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}
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mappings = CALLOC(ranges, struct map_range);
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if (!mappings) {
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fprintf(log_get_logfd(), _( "%s: Memory allocation failure\n"),
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log_get_progname());
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return NULL;
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}
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/* Gather up the ranges from the command line */
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m = mappings;
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for (int i = 0; i < ranges * 3; i+=3, m++) {
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if (a2ul(&m->upper, argv[i + 0], NULL, 0, 0, UINT_MAX) == -1) {
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if (errno == ERANGE)
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fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
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free(mappings);
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return NULL;
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}
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if (a2ul(&m->lower, argv[i + 1], NULL, 0, 0, UINT_MAX) == -1) {
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if (errno == ERANGE)
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fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
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free(mappings);
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return NULL;
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}
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if (a2ul(&m->count, argv[i + 2], NULL, 0, 0,
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MIN(MIN(UINT_MAX, ULONG_MAX - 1) - m->lower,
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MIN(UINT_MAX, ULONG_MAX - 1) - m->upper))
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== -1)
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{
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if (errno == ERANGE)
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fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
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free(mappings);
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return NULL;
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}
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}
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return mappings;
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}
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/* Number of ascii digits needed to print any unsigned long in decimal.
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* There are approximately 10 bits for every 3 decimal digits.
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* So from bits to digits the formula is roundup((Number of bits)/10) * 3.
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* For common sizes of integers this works out to:
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* 2bytes --> 6 ascii estimate -> 65536 (5 real)
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* 4bytes --> 12 ascii estimated -> 4294967296 (10 real)
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* 8bytes --> 21 ascii estimated -> 18446744073709551616 (20 real)
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* 16bytes --> 39 ascii estimated -> 340282366920938463463374607431768211456 (39 real)
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*/
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#define ULONG_DIGITS (((WIDTHOF(unsigned long) + 9)/10)*3)
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#if HAVE_SYS_CAPABILITY_H
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static inline bool maps_lower_root(int cap, int ranges, const struct map_range *mappings)
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{
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int idx;
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const struct map_range *mapping;
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if (cap != CAP_SETUID)
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return false;
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mapping = mappings;
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for (idx = 0; idx < ranges; idx++, mapping++) {
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if (mapping->lower == 0)
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return true;
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}
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return false;
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}
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#endif
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/*
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* The ruid refers to the caller's uid and is used to reset the effective uid
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* back to the callers real uid.
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* This clutch mainly exists for setuid-based new{g,u}idmap binaries that are
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* called in contexts where all capabilities other than the necessary
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* CAP_SET{G,U}ID capabilities are dropped. Since the kernel will require
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* assurance that the caller holds CAP_SYS_ADMIN over the target user namespace
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* the only way it can confirm is in this case is if the effective uid is
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* equivalent to the uid owning the target user namespace.
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* Note, we only support this when a) new{g,u}idmap is not called by root and
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* b) if the caller's uid and the uid retrieved via system appropriate means
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* (shadow file or other) are identical. Specifically, this does not support
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* when the root user calls the new{g,u}idmap binary for an unprivileged user.
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* If this is wanted: use file capabilities!
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*/
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void write_mapping(int proc_dir_fd, int ranges, const struct map_range *mappings,
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const char *map_file, uid_t ruid)
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{
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int idx;
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const struct map_range *mapping;
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size_t bufsize;
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char *buf, *pos, *end;
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int fd;
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#if HAVE_SYS_CAPABILITY_H
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int cap;
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struct __user_cap_header_struct hdr = {_LINUX_CAPABILITY_VERSION_3, 0};
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struct __user_cap_data_struct data[2] = {{0}};
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if (strcmp(map_file, "uid_map") == 0) {
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cap = CAP_SETUID;
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} else if (strcmp(map_file, "gid_map") == 0) {
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cap = CAP_SETGID;
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} else {
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fprintf(log_get_logfd(), _("%s: Invalid map file %s specified\n"), log_get_progname(), map_file);
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exit(EXIT_FAILURE);
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}
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/* Align setuid- and fscaps-based new{g,u}idmap behavior. */
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if (geteuid() == 0 && geteuid() != ruid) {
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if (prctl(PR_SET_KEEPCAPS, 1L) == -1) {
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fprintf(log_get_logfd(), _("%s: Could not prctl(PR_SET_KEEPCAPS)\n"), log_get_progname());
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exit(EXIT_FAILURE);
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}
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if (seteuid(ruid) < 0) {
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fprintf(log_get_logfd(), _("%s: Could not seteuid to %d\n"), log_get_progname(), ruid);
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exit(EXIT_FAILURE);
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}
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}
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/* Lockdown new{g,u}idmap by dropping all unneeded capabilities. */
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bzero(data, sizeof(data));
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data[0].effective = CAP_TO_MASK(cap);
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/*
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* When uid 0 from the ancestor userns is supposed to be mapped into
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* the child userns we need to retain CAP_SETFCAP.
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*/
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if (maps_lower_root(cap, ranges, mappings))
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data[0].effective |= CAP_TO_MASK(CAP_SETFCAP);
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data[0].permitted = data[0].effective;
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if (capset(&hdr, data) < 0) {
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fprintf(log_get_logfd(), _("%s: Could not set caps\n"), log_get_progname());
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exit(EXIT_FAILURE);
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}
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#endif
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bufsize = (ULONG_DIGITS + 1) * 3 * ranges + 1;
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pos = buf = XMALLOC(bufsize, char);
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end = buf + bufsize;
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/* Build the mapping command */
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mapping = mappings;
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for (idx = 0; idx < ranges; idx++, mapping++) {
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/* Append this range to the string that will be written */
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pos = stpeprintf(pos, end, "%lu %lu %lu\n",
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mapping->upper,
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mapping->lower,
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mapping->count);
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}
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if (pos == end || pos == NULL) {
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fprintf(log_get_logfd(), _("%s: stpeprintf failed!\n"), log_get_progname());
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exit(EXIT_FAILURE);
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}
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/* Write the mapping to the mapping file */
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fd = openat(proc_dir_fd, map_file, O_WRONLY);
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if (fd < 0) {
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fprintf(log_get_logfd(), _("%s: open of %s failed: %s\n"),
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log_get_progname(), map_file, strerror(errno));
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exit(EXIT_FAILURE);
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}
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if (write_full(fd, buf, pos - buf) == -1) {
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fprintf(log_get_logfd(), _("%s: write to %s failed: %s\n"),
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log_get_progname(), map_file, strerror(errno));
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exit(EXIT_FAILURE);
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}
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if (close(fd) != 0 && errno != EINTR) {
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fprintf(log_get_logfd(), _("%s: closing %s failed: %s\n"),
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log_get_progname(), map_file, strerror(errno));
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exit(EXIT_FAILURE);
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}
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free(buf);
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}
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