shadow/src/newgidmap.c
Serge Hallyn 2b22a6909d libsubid: don't print error messages on stderr by default
Closes #325

Add a new subid_init() function which can be used to specify the
stream on which error messages should be printed.  (If you want to
get fancy you can redirect that to memory :)  If subid_init() is
not called, use stderr.  If NULL is passed, then /dev/null will
be used.

This patch also fixes up the 'Prog', which previously had to be
defined by any program linking against libsubid.  Now, by default
in libsubid it will show (subid).  Once subid_init() is called,
it will use the first variable passed to subid_init().

Signed-off-by: Serge Hallyn <serge@hallyn.com>
2021-05-15 12:38:55 -05:00

261 lines
7.4 KiB
C

/*
* Copyright (c) 2013 Eric Biederman
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the copyright holders or contributors may not be used to
* endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <config.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "defines.h"
#include "prototypes.h"
#include "subordinateio.h"
#include "getdef.h"
#include "idmapping.h"
/*
* Global variables
*/
const char *Prog;
FILE *shadow_logfd = NULL;
static bool verify_range(struct passwd *pw, struct map_range *range, bool *allow_setgroups)
{
/* An empty range is invalid */
if (range->count == 0)
return false;
/* Test /etc/subgid. If the mapping is valid then we allow setgroups. */
if (have_sub_gids(pw->pw_name, range->lower, range->count)) {
*allow_setgroups = true;
return true;
}
/* Allow a process to map its own gid. */
if ((range->count == 1) && (getgid() == range->lower)) {
/* noop -- if setgroups is enabled already we won't disable it. */
return true;
}
return false;
}
static void verify_ranges(struct passwd *pw, int ranges,
struct map_range *mappings, bool *allow_setgroups)
{
struct map_range *mapping;
int idx;
mapping = mappings;
for (idx = 0; idx < ranges; idx++, mapping++) {
if (!verify_range(pw, mapping, allow_setgroups)) {
fprintf(stderr, _( "%s: gid range [%lu-%lu) -> [%lu-%lu) not allowed\n"),
Prog,
mapping->upper,
mapping->upper + mapping->count,
mapping->lower,
mapping->lower + mapping->count);
exit(EXIT_FAILURE);
}
}
}
static void usage(void)
{
fprintf(stderr, _("usage: %s <pid> <gid> <lowergid> <count> [ <gid> <lowergid> <count> ] ... \n"), Prog);
exit(EXIT_FAILURE);
}
void write_setgroups(int proc_dir_fd, bool allow_setgroups)
{
int setgroups_fd;
char *policy, policy_buffer[4096];
/*
* Default is "deny", and any "allow" will out-rank a "deny". We don't
* forcefully write an "allow" here because the process we are writing
* mappings for may have already set themselves to "deny" (and "allow"
* is the default anyway). So allow_setgroups == true is a noop.
*/
policy = "deny\n";
if (allow_setgroups)
return;
setgroups_fd = openat(proc_dir_fd, "setgroups", O_RDWR|O_CLOEXEC);
if (setgroups_fd < 0) {
/*
* If it's an ENOENT then we are on too old a kernel for the setgroups
* code to exist. Emit a warning and bail on this.
*/
if (ENOENT == errno) {
fprintf(stderr, _("%s: kernel doesn't support setgroups restrictions\n"), Prog);
goto out;
}
fprintf(stderr, _("%s: couldn't open process setgroups: %s\n"),
Prog,
strerror(errno));
exit(EXIT_FAILURE);
}
/*
* Check whether the policy is already what we want. /proc/self/setgroups
* is write-once, so attempting to write after it's already written to will
* fail.
*/
if (read(setgroups_fd, policy_buffer, sizeof(policy_buffer)) < 0) {
fprintf(stderr, _("%s: failed to read setgroups: %s\n"),
Prog,
strerror(errno));
exit(EXIT_FAILURE);
}
if (!strncmp(policy_buffer, policy, strlen(policy)))
goto out;
/* Write the policy. */
if (lseek(setgroups_fd, 0, SEEK_SET) < 0) {
fprintf(stderr, _("%s: failed to seek setgroups: %s\n"),
Prog,
strerror(errno));
exit(EXIT_FAILURE);
}
if (dprintf(setgroups_fd, "%s", policy) < 0) {
fprintf(stderr, _("%s: failed to setgroups %s policy: %s\n"),
Prog,
policy,
strerror(errno));
exit(EXIT_FAILURE);
}
out:
close(setgroups_fd);
}
/*
* newgidmap - Set the gid_map for the specified process
*/
int main(int argc, char **argv)
{
char proc_dir_name[32];
char *target_str;
pid_t target;
int proc_dir_fd;
int ranges;
struct map_range *mappings;
struct stat st;
struct passwd *pw;
int written;
bool allow_setgroups = false;
Prog = Basename (argv[0]);
shadow_logfd = stderr;
/*
* The valid syntax are
* newgidmap target_pid
*/
if (argc < 2)
usage();
/* Find the process that needs its user namespace
* gid mapping set.
*/
target_str = argv[1];
if (!get_pid(target_str, &target))
usage();
/* max string length is 6 + 10 + 1 + 1 = 18, allocate 32 bytes */
written = snprintf(proc_dir_name, sizeof(proc_dir_name), "/proc/%u/",
target);
if ((written <= 0) || (written >= sizeof(proc_dir_name))) {
fprintf(stderr, "%s: snprintf of proc path failed: %s\n",
Prog, strerror(errno));
}
proc_dir_fd = open(proc_dir_name, O_DIRECTORY);
if (proc_dir_fd < 0) {
fprintf(stderr, _("%s: Could not open proc directory for target %u\n"),
Prog, target);
return EXIT_FAILURE;
}
/* Who am i? */
pw = get_my_pwent ();
if (NULL == pw) {
fprintf (stderr,
_("%s: Cannot determine your user name.\n"),
Prog);
SYSLOG ((LOG_WARN, "Cannot determine the user name of the caller (UID %lu)",
(unsigned long) getuid ()));
return EXIT_FAILURE;
}
/* Get the effective uid and effective gid of the target process */
if (fstat(proc_dir_fd, &st) < 0) {
fprintf(stderr, _("%s: Could not stat directory for target %u\n"),
Prog, target);
return EXIT_FAILURE;
}
/* Verify real user and real group matches the password entry
* and the effective user and group of the program whose
* mappings we have been asked to set.
*/
if ((getuid() != pw->pw_uid) ||
(!getdef_bool("GRANT_AUX_GROUP_SUBIDS") && (getgid() != pw->pw_gid)) ||
(pw->pw_uid != st.st_uid) ||
(getgid() != st.st_gid)) {
fprintf(stderr, _( "%s: Target %u is owned by a different user: uid:%lu pw_uid:%lu st_uid:%lu, gid:%lu pw_gid:%lu st_gid:%lu\n" ),
Prog, target,
(unsigned long int)getuid(), (unsigned long int)pw->pw_uid, (unsigned long int)st.st_uid,
(unsigned long int)getgid(), (unsigned long int)pw->pw_gid, (unsigned long int)st.st_gid);
return EXIT_FAILURE;
}
if (!sub_gid_open(O_RDONLY)) {
return EXIT_FAILURE;
}
ranges = ((argc - 2) + 2) / 3;
mappings = get_map_ranges(ranges, argc - 2, argv + 2);
if (!mappings)
usage();
verify_ranges(pw, ranges, mappings, &allow_setgroups);
write_setgroups(proc_dir_fd, allow_setgroups);
write_mapping(proc_dir_fd, ranges, mappings, "gid_map", pw->pw_uid);
sub_gid_close();
return EXIT_SUCCESS;
}