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xfstests: add nsexec user namespace helper

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Add new program nsexec to facilitate creating/entering a user namespace. The
original source for the program is https://lwn.net/Articles/539940. I added
the -s option to become "root" in the user namespace.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Reviewed-by: <rjohnston@sgi.com>
Signed-off-by: <rjohnston@sgi.com>
This commit is contained in:
Dwight Engen
2013-06-27 16:03:28 +00:00
committed by Rich Johnston
parent 0150222d1c
commit 3f424be639
3 changed files with 241 additions and 1 deletions
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.gitignore
+1
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@@ -64,6 +64,7 @@
/src/mmapcat
/src/multi_open_unlink
/src/nametest
/src/nsexec
/src/permname
/src/preallo_rw_pattern_reader
/src/preallo_rw_pattern_writer
src/Makefile
+1 -1
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@@ -18,7 +18,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
locktest unwritten_mmap bulkstat_unlink_test t_stripealign \
bulkstat_unlink_test_modified t_dir_offset t_futimens t_immutable \
stale_handle pwrite_mmap_blocked t_dir_offset2 seek_sanity_test \
seek_copy_test t_readdir_1 t_readdir_2 fsync-tester
seek_copy_test t_readdir_1 t_readdir_2 fsync-tester nsexec
SUBDIRS =
src/nsexec.c
+239
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@@ -0,0 +1,239 @@
/* userns_child_exec.c
Copyright 2013, Michael Kerrisk
Licensed under GNU General Public License v2 or later
Create a child process that executes a shell command in new
namespace(s); allow UID and GID mappings to be specified when
creating a user namespace.
*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <sched.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <signal.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <errno.h>
/* A simple error-handling function: print an error message based
on the value in 'errno' and terminate the calling process */
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)
struct child_args {
char **argv; /* Command to be executed by child, with arguments */
int pipe_fd[2]; /* Pipe used to synchronize parent and child */
};
static int verbose, setid;
static void
usage(char *pname)
{
fprintf(stderr, "Usage: %s [options] cmd [arg...]\n\n", pname);
fprintf(stderr, "Create a child process that executes a shell command "
"in a new user namespace,\n"
"and possibly also other new namespace(s).\n\n");
fprintf(stderr, "Options can be:\n\n");
#define fpe(str) fprintf(stderr, " %s", str);
fpe("-i New IPC namespace\n");
fpe("-m New mount namespace\n");
fpe("-n New network namespace\n");
fpe("-p New PID namespace\n");
fpe("-u New UTS namespace\n");
fpe("-U New user namespace\n");
fpe("-M uid_map Specify UID map for user namespace\n");
fpe("-G gid_map Specify GID map for user namespace\n");
fpe(" If -M or -G is specified, -U is required\n");
fpe("-s Set uid/gid to 0 in the new user namespace\n");
fpe("-v Display verbose messages\n");
fpe("\n");
fpe("Map strings for -M and -G consist of records of the form:\n");
fpe("\n");
fpe(" ID-inside-ns ID-outside-ns len\n");
fpe("\n");
fpe("A map string can contain multiple records, separated by commas;\n");
fpe("the commas are replaced by newlines before writing to map files.\n");
exit(EXIT_FAILURE);
}
/* Update the mapping file 'map_file', with the value provided in
'mapping', a string that defines a UID or GID mapping. A UID or
GID mapping consists of one or more newline-delimited records
of the form:
ID_inside-ns ID-outside-ns length
Requiring the user to supply a string that contains newlines is
of course inconvenient for command-line use. Thus, we permit the
use of commas to delimit records in this string, and replace them
with newlines before writing the string to the file. */
static void
update_map(char *mapping, char *map_file)
{
int fd, j;
size_t map_len; /* Length of 'mapping' */
/* Replace commas in mapping string with newlines */
map_len = strlen(mapping);
for (j = 0; j < map_len; j++)
if (mapping[j] == ',')
mapping[j] = '\n';
fd = open(map_file, O_RDWR);
if (fd == -1) {
fprintf(stderr, "open %s: %s\n", map_file, strerror(errno));
exit(EXIT_FAILURE);
}
if (write(fd, mapping, map_len) != map_len) {
fprintf(stderr, "write %s: %s\n", map_file, strerror(errno));
exit(EXIT_FAILURE);
}
close(fd);
}
static int /* Start function for cloned child */
childFunc(void *arg)
{
struct child_args *args = (struct child_args *) arg;
char ch;
/* Wait until the parent has updated the UID and GID mappings. See
the comment in main(). We wait for end of file on a pipe that will
be closed by the parent process once it has updated the mappings. */
close(args->pipe_fd[1]); /* Close our descriptor for the write end
of the pipe so that we see EOF when
parent closes its descriptor */
if (read(args->pipe_fd[0], &ch, 1) != 0) {
fprintf(stderr, "Failure in child: read from pipe returned != 0\n");
exit(EXIT_FAILURE);
}
if (setid) {
if (setgid(0) < 0)
fprintf(stderr, "Failure in child to setgid 0: %s\n", strerror(errno));
if (setuid(0) < 0)
fprintf(stderr, "Failure in child to setuid 0: %s\n", strerror(errno));
}
/* Execute a shell command */
execvp(args->argv[0], args->argv);
errExit("execvp");
}
#define STACK_SIZE (1024 * 1024)
static char child_stack[STACK_SIZE]; /* Space for child's stack */
int
main(int argc, char *argv[])
{
int flags, opt;
pid_t child_pid;
struct child_args args;
char *uid_map, *gid_map;
char map_path[PATH_MAX];
/* Parse command-line options. The initial '+' character in
the final getopt() argument prevents GNU-style permutation
of command-line options. That's useful, since sometimes
the 'command' to be executed by this program itself
has command-line options. We don't want getopt() to treat
those as options to this program. */
flags = 0;
verbose = 0;
setid = 0;
gid_map = NULL;
uid_map = NULL;
while ((opt = getopt(argc, argv, "+imnpuUM:G:vs")) != -1) {
switch (opt) {
case 'i': flags |= CLONE_NEWIPC; break;
case 'm': flags |= CLONE_NEWNS; break;
case 'n': flags |= CLONE_NEWNET; break;
case 'p': flags |= CLONE_NEWPID; break;
case 'u': flags |= CLONE_NEWUTS; break;
case 'v': verbose = 1; break;
case 'M': uid_map = optarg; break;
case 'G': gid_map = optarg; break;
case 'U': flags |= CLONE_NEWUSER; break;
case 's': setid = 1; break;
default: usage(argv[0]);
}
}
/* -M or -G without -U is nonsensical */
if ((uid_map != NULL || gid_map != NULL) &&
!(flags & CLONE_NEWUSER))
usage(argv[0]);
args.argv = &argv[optind];
/* We use a pipe to synchronize the parent and child, in order to
ensure that the parent sets the UID and GID maps before the child
calls execve(). This ensures that the child maintains its
capabilities during the execve() in the common case where we
want to map the child's effective user ID to 0 in the new user
namespace. Without this synchronization, the child would lose
its capabilities if it performed an execve() with nonzero
user IDs (see the capabilities(7) man page for details of the
transformation of a process's capabilities during execve()). */
if (pipe(args.pipe_fd) == -1)
errExit("pipe");
/* Create the child in new namespace(s) */
child_pid = clone(childFunc, child_stack + STACK_SIZE,
flags | SIGCHLD, &args);
if (child_pid == -1)
errExit("clone");
/* Parent falls through to here */
if (verbose)
printf("%s: PID of child created by clone() is %ld\n",
argv[0], (long) child_pid);
/* Update the UID and GID maps in the child */
if (uid_map != NULL) {
snprintf(map_path, PATH_MAX, "/proc/%ld/uid_map",
(long) child_pid);
update_map(uid_map, map_path);
}
if (gid_map != NULL) {
snprintf(map_path, PATH_MAX, "/proc/%ld/gid_map",
(long) child_pid);
update_map(gid_map, map_path);
}
/* Close the write end of the pipe, to signal to the child that we
have updated the UID and GID maps */
close(args.pipe_fd[1]);
if (waitpid(child_pid, NULL, 0) == -1) /* Wait for child */
errExit("waitpid");
if (verbose)
printf("%s: terminating\n", argv[0]);
exit(EXIT_SUCCESS);
}