On Mon, Jun 18, 2018 at 08:34:50PM -0700, Andrei Vagin wrote:

Hi David,

We run CRIU tests for vfs/for-next, and today a few of these test failed. I
found that the problem appears after this patch..

quoted

 int pid_ns_prepare_proc(struct pid_namespace *ns)
 {
+	struct proc_fs_context *ctx;
+	struct fs_context *fc;
 	struct vfsmount *mnt;
+	int ret;
+
+	fc = vfs_new_fs_context(&proc_fs_type, NULL, 0,
+				FS_CONTEXT_FOR_KERNEL_MOUNT);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+
+	ctx = container_of(fc, struct proc_fs_context, fc);
+	if (ctx->pid_ns != ns) {
+		put_pid_ns(ctx->pid_ns);
+		get_pid_ns(ns);
+		ctx->pid_ns = ns;
+	}
+
+	ret = vfs_get_tree(fc);
+	if (ret < 0) {
+		put_fs_context(fc);
+		return ret;
+	}
 
-	mnt = kern_mount_data(&proc_fs_type, ns, 0);

Here ns->user_ns and get_current_cred()->user_ns are not always equal

quoted

+	mnt = vfs_create_mount(fc);
+	put_fs_context(fc);
 	if (IS_ERR(mnt))
 		return PTR_ERR(mnt);
 

#define _GNU_SOURCE
#include <sys/types.h>
#include <sched.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/mount.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <grp.h>
#include <linux/limits.h>


#define NS_STACK_SIZE	4096

#define __stack_aligned__	__attribute__((aligned(16)))

/* All arguments should be above stack, because it grows down */
struct ns_exec_args {
	char stack[NS_STACK_SIZE] __stack_aligned__;
	char stack_ptr[0];
	int pfd[2];
};

static int ns_exec(void *_arg)
{
	struct ns_exec_args *args = (struct ns_exec_args *) _arg;
	int ret;

	close(args->pfd[1]);
	if (read(args->pfd[0], &ret, sizeof(ret)) != sizeof(ret))
		return -1;

	setsid();

	if (setuid(0) || setgid(0) || setgroups(0, NULL)) {
		fprintf(stderr, "set*id failed: %m\n");
		return -1;
	}

	if (mount("proc", "/mnt", "proc", MS_MGC_VAL | MS_NOSUID | MS_NOEXEC | MS_NODEV, NULL)) {
		fprintf(stderr, "mount(/proc) failed: %m\n");
		return -1;
	}

	return 0;
}

#define UID_MAP "0 100000 100000\n100000 200000 50000"
#define GID_MAP "0 400000 50000\n50000 500000 100000"
int main()
{
	pid_t pid;
	int ret, status;
	struct ns_exec_args args;
	int flags;
	char pname[PATH_MAX];
	int fd, pfd[2];

	if (pipe(pfd))
		return 1;

	args.pfd[0] = pfd[0];
	args.pfd[1] = pfd[1];

	flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWUTS |
		CLONE_NEWNET | CLONE_NEWIPC | CLONE_NEWUSER | SIGCHLD;

	pid = clone(ns_exec, args.stack_ptr, flags, &args);
	if (pid < 0) {
		fprintf(stderr, "clone() failed: %m\n");
		exit(1);
	}


	snprintf(pname, sizeof(pname), "/proc/%d/uid_map", pid);
	fd = open(pname, O_WRONLY);
	if (fd < 0) {
		fprintf(stderr, "open(%s): %m\n", pname);
		exit(1);
	}
	if (write(fd, UID_MAP, sizeof(UID_MAP)) < 0) {
		fprintf(stderr, "write(" UID_MAP "): %m\n");
		exit(1);
	}
	close(fd);

	snprintf(pname, sizeof(pname), "/proc/%d/gid_map", pid);
	fd = open(pname, O_WRONLY);
	if (fd < 0) {
		fprintf(stderr, "open(%s): %m\n", pname);
		exit(1);
	}
	if (write(fd, GID_MAP, sizeof(GID_MAP)) < 0) {
		fprintf(stderr, "write(" GID_MAP "): %m\n");
		exit(1);
	}
	close(fd);

	if (write(pfd[1], &ret, sizeof(ret)) != sizeof(ret))
		return 1;

	if (waitpid(pid, &status, 0) != pid)
		return 1;
	if (status)
		return 1;

	return 0;
}

--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html