Merge pull request #977 from richardmaw-codethink/machinectl-userns-login-v2

Fix machinectl login with containers in user namespaces (v2)

1 files changed, 38 insertions, 7 deletions

diff --git a/src/basic/util.c b/src/basic/util.c
index ebfc6c6a72..9571f0ab12 100644
--- a/src/basic/util.c
+++ b/src/basic/util.c
@@ -4950,8 +4950,8 @@ int container_get_leader(const char *machine, pid_t *pid) {
         return 0;
 }
 
-int namespace_open(pid_t pid, int *pidns_fd, int *mntns_fd, int *netns_fd, int *root_fd) {
-        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, netnsfd = -1;
+int namespace_open(pid_t pid, int *pidns_fd, int *mntns_fd, int *netns_fd, int *userns_fd, int *root_fd) {
+        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, netnsfd = -1, usernsfd = -1;
         int rfd = -1;
 
         assert(pid >= 0);
@@ -4983,6 +4983,15 @@ int namespace_open(pid_t pid, int *pidns_fd, int *mntns_fd, int *netns_fd, int *
                         return -errno;
         }
 
+        if (userns_fd) {
+                const char *userns;
+
+                userns = procfs_file_alloca(pid, "ns/user");
+                usernsfd = open(userns, O_RDONLY|O_NOCTTY|O_CLOEXEC);
+                if (usernsfd < 0 && errno != ENOENT)
+                        return -errno;
+        }
+
         if (root_fd) {
                 const char *root;
 
@@ -5001,15 +5010,33 @@ int namespace_open(pid_t pid, int *pidns_fd, int *mntns_fd, int *netns_fd, int *
         if (netns_fd)
                 *netns_fd = netnsfd;
 
+        if (userns_fd)
+                *userns_fd = usernsfd;
+
         if (root_fd)
                 *root_fd = rfd;
 
-        pidnsfd = mntnsfd = netnsfd = -1;
+        pidnsfd = mntnsfd = netnsfd = usernsfd = -1;
 
         return 0;
 }
 
-int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int root_fd) {
+int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int userns_fd, int root_fd) {
+        if (userns_fd >= 0) {
+                /* Can't setns to your own userns, since then you could
+                 * escalate from non-root to root in your own namespace, so
+                 * check if namespaces equal before attempting to enter. */
+                _cleanup_free_ char *userns_fd_path = NULL;
+                int r;
+                if (asprintf(&userns_fd_path, "/proc/self/fd/%d", userns_fd) < 0)
+                        return -ENOMEM;
+
+                r = files_same(userns_fd_path, "/proc/self/ns/user");
+                if (r < 0)
+                        return r;
+                if (r)
+                        userns_fd = -1;
+        }
 
         if (pidns_fd >= 0)
                 if (setns(pidns_fd, CLONE_NEWPID) < 0)
@@ -5023,6 +5050,10 @@ int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int root_fd) {
                 if (setns(netns_fd, CLONE_NEWNET) < 0)
                         return -errno;
 
+        if (userns_fd >= 0)
+                if (setns(userns_fd, CLONE_NEWUSER) < 0)
+                        return -errno;
+
         if (root_fd >= 0) {
                 if (fchdir(root_fd) < 0)
                         return -errno;
@@ -6038,7 +6069,7 @@ int ptsname_malloc(int fd, char **ret) {
 }
 
 int openpt_in_namespace(pid_t pid, int flags) {
-        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, rootfd = -1;
+        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1;
         _cleanup_close_pair_ int pair[2] = { -1, -1 };
         union {
                 struct cmsghdr cmsghdr;
@@ -6055,7 +6086,7 @@ int openpt_in_namespace(pid_t pid, int flags) {
 
         assert(pid > 0);
 
-        r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &rootfd);
+        r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &usernsfd, &rootfd);
         if (r < 0)
                 return r;
 
@@ -6071,7 +6102,7 @@ int openpt_in_namespace(pid_t pid, int flags) {
 
                 pair[0] = safe_close(pair[0]);
 
-                r = namespace_enter(pidnsfd, mntnsfd, -1, rootfd);
+                r = namespace_enter(pidnsfd, mntnsfd, -1, usernsfd, rootfd);
                 if (r < 0)
                         _exit(EXIT_FAILURE);