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