"Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes:
> I would like to write code that discovers the namespace setup on a live
> system. The NS_GET_PARENT and NS_GET_USERNS ioctl() operations added in
> Linux 4.9 provide much of what I want, but there are still a couple of
> small pieces missing. Those pieces are added with this patch series.
So it looks like the -EOVERFLOW change broke your example program.
Causing it to abort if -EOVERFLOW is hit. Do we really want to return
-EOVERFLOW? Or do you want to fix your program?
Eric
> Here's an example program that makes use of the new ioctl() operations.
>
> 8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---
> /* ns_capable.c
>
> (C) 2016 Michael Kerrisk, <mtk.manpages@xxxxxxxxx>
>
> Licensed under the GNU General Public License v2 or later.
>
> Test whether a process (identified by PID) might (subject to LSM checks)
> have capabilities in a namespace (identified by a /proc/PID/ns/xxx file).
> */
> #define _GNU_SOURCE
> #include <sched.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <errno.h>
> #include <fcntl.h>
> #include <string.h>
> #include <sys/stat.h>
> #include <sys/ioctl.h>
> #include <limits.h>
> #include <sys/capability.h>
>
> #ifndef NS_GET_USERNS
> #define NSIO 0xb7
> #define NS_GET_USERNS _IO(NSIO, 0x1)
> #define NS_GET_PARENT _IO(NSIO, 0x2)
> #define NS_GET_NSTYPE _IO(NSIO, 0x3)
> #define NS_GET_OWNER_UID _IO(NSIO, 0x4)
> #endif
>
> #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
> } while (0)
>
> #define fatal(msg) do { fprintf(stderr, "%s\n", msg); \
> exit(EXIT_FAILURE); } while (0)
>
> /* Display capabilities sets of process with specified PID */
>
> static void
> show_cap(pid_t pid)
> {
> cap_t caps;
> char *cap_string;
>
> caps = cap_get_pid(pid);
> if (caps == NULL)
> errExit("cap_get_proc");
>
> cap_string = cap_to_text(caps, NULL);
> if (cap_string == NULL)
> errExit("cap_to_text");
>
> printf("Capabilities: %s\n", cap_string);
> }
>
> /* Obtain the effective UID pf the process 'pid' by
> scanning its /proc/PID/file */
>
> static uid_t
> get_euid_of_process(pid_t pid)
> {
> char path[PATH_MAX];
> char line[1024];
> int uid;
>
> snprintf(path, sizeof(path), "/proc/%ld/status", (long) pid);
>
> FILE *fp;
> fp = fopen(path, "r");
> if (fp == NULL)
> errExit("fopen-/proc/PID/status");
>
> for (;;) {
> if (fgets(line, sizeof(line), fp) == NULL) {
>
> /* Should never happen... */
>
> fprintf(stderr, "Failure scanning %s\n", path);
> exit(EXIT_FAILURE);
> }
>
> if (strstr(line, "Uid:") == line) {
> sscanf(line, "Uid: %*d %d %*d %*d", &uid);
> return uid;
> }
> }
> }
>
> int
> main(int argc, char *argv[])
> {
> int ns_fd, userns_fd, pid_userns_fd;
> int nstype;
> int next_fd;
> struct stat pid_stat;
> struct stat target_stat;
> char *pid_str;
> pid_t pid;
> char path[PATH_MAX];
>
> if (argc < 2) {
> fprintf(stderr, "Usage: %s PID [ns-file]\n", argv[0]);
> fprintf(stderr, "\t'ns-file' is a /proc/PID/ns/xxxx file; "
> "if omitted, use the namespace\n"
> "\treferred to by standard input "
> "(file descriptor 0)\n");
> exit(EXIT_FAILURE);
> }
>
> pid_str = argv[1];
> pid = atoi(pid_str);
>
> if (argc <= 2) {
> ns_fd = STDIN_FILENO;
> } else {
> ns_fd = open(argv[2], O_RDONLY);
> if (ns_fd == -1)
> errExit("open-ns-file");
> }
>
> /* Get the relevant user namespace FD, which is 'ns_fd' if 'ns_fd' refers
> to a user namespace, otherwise the user namespace that owns 'ns_fd' */
>
> nstype = ioctl(ns_fd, NS_GET_NSTYPE);
> if (nstype == -1)
> errExit("ioctl-NS_GET_NSTYPE");
>
> if (nstype == CLONE_NEWUSER) {
> userns_fd = ns_fd;
> } else {
> userns_fd = ioctl(ns_fd, NS_GET_USERNS);
> if (userns_fd == -1)
> errExit("ioctl-NS_GET_USERNS");
> }
>
> /* Obtain 'stat' info for the user namespace of the specified PID */
>
> snprintf(path, sizeof(path), "/proc/%s/ns/user", pid_str);
>
> pid_userns_fd = open(path, O_RDONLY);
> if (pid_userns_fd == -1)
> errExit("open-PID");
>
> if (fstat(pid_userns_fd, &pid_stat) == -1)
> errExit("fstat-PID");
>
> /* Get 'stat' info for the target user namesapce */
>
> if (fstat(userns_fd, &target_stat) == -1)
> errExit("fstat-PID");
>
> /* If the PID is in the target user namespace, then it has
> whatever capabilities are in its sets. */
>
> if (pid_stat.st_dev == target_stat.st_dev &&
> pid_stat.st_ino == target_stat.st_ino) {
> printf("PID is in target namespace\n");
> printf("Subject to LSM checks, it has the following capabilities\n");
>
> show_cap(pid);
>
> exit(EXIT_SUCCESS);
> }
>
> /* Otherwise, we need to walk through the ancestors of the target
> user namespace to see if PID is in an ancestor namespace */
>
> for (;;) {
> int f;
>
> next_fd = ioctl(userns_fd, NS_GET_PARENT);
>
> if (next_fd == -1) {
>
> /* The error here should be EPERM... */
>
> if (errno != EPERM)
> errExit("ioctl-NS_GET_PARENT");
>
> printf("PID is not in an ancestor namespace\n");
> printf("It has no capabilities in the target namespace\n");
>
> exit(EXIT_SUCCESS);
> }
>
> if (fstat(next_fd, &target_stat) == -1)
> errExit("fstat-PID");
>
> /* If the 'stat' info for this user namespace matches the 'stat'
> * info for 'next_fd', then the PID is in an ancestor namespace */
>
> if (pid_stat.st_dev == target_stat.st_dev &&
> pid_stat.st_ino == target_stat.st_ino)
> break;
>
> /* Next time round, get the next parent */
>
> f = userns_fd;
> userns_fd = next_fd;
> close(f);
> }
>
> /* At this point, we found that PID is in an ancestor of the target
> user namespace, and 'userns_fd' refers to the immediate descendant
> user namespace of PID in the chain of user namespaces from PID to
> the target user namespace. If the effective UID of PID matches the
> owner UID of descendant user namespace, then PID has all
> capabilities in the descendant namespace(s); otherwise, it just has
> the capabilities that are in its sets. */
>
> uid_t owner_uid, uid;
> if (ioctl(userns_fd, NS_GET_OWNER_UID, &owner_uid) == -1) {
> perror("ioctl-NS_GET_OWNER_UID");
> exit(EXIT_FAILURE);
> }
>
> uid = get_euid_of_process(pid);
>
> printf("PID is in an ancestor namespace\n");
> if (owner_uid == uid) {
> printf("And its effective UID matches the owner "
> "of the namespace\n");
> printf("Subject to LSM checks, PID has all capabilities in "
> "that namespace!\n");
> } else {
> printf("But its effective UID does not match the owner "
> "of the namespace\n");
> printf("Subject to LSM checks, it has the following capabilities\n");
> show_cap(pid);
> }
>
> exit(EXIT_SUCCESS);
> }
> 8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---8x---
>
> Michael Kerrisk (2):
> nsfs: Add an ioctl() to return the namespace type
> nsfs: Add an ioctl() to return owner UID of a userns
>
> fs/nsfs.c | 15 +++++++++++++++
> include/uapi/linux/nsfs.h | 9 +++++++--
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> --
> 2.5.5
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
