[PATCH 4/4 v5 RESEND] selftests: add devpts selftests

Christian Brauner
2018-03-13T16:55:27Z

This adds tests to check:
- bind-mounts from /dev/pts/ptmx to /dev/ptmx work
- non-standard mounts of devpts work
- bind-mounts of /dev/pts/ptmx to locations that do not resolve to a valid
slave pty path under the originating devpts mount fail

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---
ChangeLog v4->v5:
* extend tests to verify failure on ptmx devices located outside the
devpts mount without a common ancestor directory
ChangeLog v3->v4:
* patch unchanged
ChangeLog v2->v3:
* extend test for non-standard devpts mounts such as
mount -t devpts e devpts /mnt
ChangeLog v1->v2:
* patch added
ChangeLog v0->v1:
* patch not present
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/filesystems/.gitignore | 1 +
tools/testing/selftests/filesystems/Makefile | 2 +-
tools/testing/selftests/filesystems/devpts_pts.c | 313 +++++++++++++++++++++++
4 files changed, 316 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/filesystems/devpts_pts.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 7442dfb73b7f..dbda89c9d9b9 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -7,6 +7,7 @@ TARGETS += cpufreq
TARGETS += cpu-hotplug
TARGETS += efivarfs
TARGETS += exec
+TARGETS += filesystems
TARGETS += firmware
TARGETS += ftrace
TARGETS += futex
diff --git a/tools/testing/selftests/filesystems/.gitignore b/tools/testing/selftests/filesystems/.gitignore
index 31d6e426b6d4..8449cf6716ce 100644
--- a/tools/testing/selftests/filesystems/.gitignore
+++ b/tools/testing/selftests/filesystems/.gitignore
@@ -1 +1,2 @@
dnotify_test
+devpts_pts
diff --git a/tools/testing/selftests/filesystems/Makefile b/tools/testing/selftests/filesystems/Makefile
index 13a73bf725b5..4e6d09fb166f 100644
--- a/tools/testing/selftests/filesystems/Makefile
+++ b/tools/testing/selftests/filesystems/Makefile
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
-TEST_PROGS := dnotify_test
+TEST_PROGS := dnotify_test devpts_pts
all: $(TEST_PROGS)

include ../lib.mk
diff --git a/tools/testing/selftests/filesystems/devpts_pts.c b/tools/testing/selftests/filesystems/devpts_pts.c
new file mode 100644
index 000000000000..b9055e974289
--- /dev/null
+++ b/tools/testing/selftests/filesystems/devpts_pts.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <sys/wait.h>
+
+static bool terminal_dup2(int duplicate, int original)
+{
+ int ret;
+
+ ret = dup2(duplicate, original);
+ if (ret < 0)
+ return false;
+
+ return true;
+}
+
+static int terminal_set_stdfds(int fd)
+{
+ int i;
+
+ if (fd < 0)
+ return 0;
+
+ for (i = 0; i < 3; i++)
+ if (!terminal_dup2(fd, (int[]){STDIN_FILENO, STDOUT_FILENO,
+ STDERR_FILENO}[i]))
+ return -1;
+
+ return 0;
+}
+
+static int login_pty(int fd)
+{
+ int ret;
+
+ setsid();
+
+ ret = ioctl(fd, TIOCSCTTY, NULL);
+ if (ret < 0)
+ return -1;
+
+ ret = terminal_set_stdfds(fd);
+ if (ret < 0)
+ return -1;
+
+ if (fd > STDERR_FILENO)
+ close(fd);
+
+ return 0;
+}
+
+static int wait_for_pid(pid_t pid)
+{
+ int status, ret;
+
+again:
+ ret = waitpid(pid, &status, 0);
+ if (ret == -1) {
+ if (errno == EINTR)
+ goto again;
+ return -1;
+ }
+ if (ret != pid)
+ goto again;
+
+ if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
+ return -1;
+
+ return 0;
+}
+
+static int resolve_procfd_symlink(int fd, char *buf, size_t buflen)
+{
+ int ret;
+ char procfd[4096];
+
+ ret = snprintf(procfd, 4096, "/proc/self/fd/%d", fd);
+ if (ret < 0 || ret >= 4096)
+ return -1;
+
+ ret = readlink(procfd, buf, buflen);
+ if (ret < 0 || (size_t)ret >= buflen)
+ return -1;
+
+ buf[ret] = '\0';
+
+ return 0;
+}
+
+static int do_tiocgptpeer(char *ptmx, char *expected_procfd_contents)
+{
+ int ret;
+ int master = -1, slave = -1, fret = -1;
+
+ master = open(ptmx, O_RDWR | O_NOCTTY | O_CLOEXEC);
+ if (master < 0) {
+ fprintf(stderr, "Failed to open \"%s\": %s\n", ptmx,
+ strerror(errno));
+ return -1;
+ }
+
+ /*
+ * grantpt() makes assumptions about /dev/pts/ so ignore it. It's also
+ * not really needed.
+ */
+ ret = unlockpt(master);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to unlock terminal\n");
+ goto do_cleanup;
+ }
+
+#ifdef TIOCGPTPEER
+ slave = ioctl(master, TIOCGPTPEER, O_RDWR | O_NOCTTY | O_CLOEXEC);
+#endif
+ if (slave < 0) {
+ if (errno == EINVAL) {
+ fprintf(stderr, "TIOCGPTPEER is not supported. "
+ "Skipping test.\n");
+ fret = EXIT_SUCCESS;
+ }
+
+ fprintf(stderr, "Failed to perform TIOCGPTPEER ioctl\n");
+ goto do_cleanup;
+ }
+
+ pid_t pid = fork();
+ if (pid < 0)
+ goto do_cleanup;
+
+ if (pid == 0) {
+ char buf[4096];
+
+ ret = login_pty(slave);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to setup terminal\n");
+ _exit(EXIT_FAILURE);
+ }
+
+ ret = resolve_procfd_symlink(STDIN_FILENO, buf, sizeof(buf));
+ if (ret < 0) {
+ fprintf(stderr, "Failed to retrieve pathname of pts "
+ "slave file descriptor\n");
+ _exit(EXIT_FAILURE);
+ }
+
+ if (strncmp(expected_procfd_contents, buf,
+ strlen(expected_procfd_contents)) != 0) {
+ fprintf(stderr, "Received invalid contents for "
+ "\"/proc/<pid>/fd/%d\" symlink: %s\n",
+ STDIN_FILENO, buf);
+ _exit(-1);
+ }
+
+ fprintf(stderr, "Contents of \"/proc/<pid>/fd/%d\" "
+ "symlink are valid: %s\n", STDIN_FILENO, buf);
+
+ _exit(EXIT_SUCCESS);
+ }
+
+ ret = wait_for_pid(pid);
+ if (ret < 0)
+ goto do_cleanup;
+
+ fret = EXIT_SUCCESS;
+
+do_cleanup:
+ if (master >= 0)
+ close(master);
+ if (slave >= 0)
+ close(slave);
+
+ return fret;
+}
+
+static int verify_non_standard_devpts_mount(void)
+{
+ char *mntpoint;
+ int ret = -1;
+ char devpts[] = P_tmpdir "/devpts_fs_XXXXXX";
+ char ptmx[] = P_tmpdir "/devpts_fs_XXXXXX/ptmx";
+
+ ret = umount("/dev/pts");
+ if (ret < 0) {
+ fprintf(stderr, "Failed to unmount \"/dev/pts\": %s\n",
+ strerror(errno));
+ return -1;
+ }
+
+ (void)umount("/dev/ptmx");
+
+ mntpoint = mkdtemp(devpts);
+ if (!mntpoint) {
+ fprintf(stderr, "Failed to create temporary mountpoint: %s\n",
+ strerror(errno));
+ return -1;
+ }
+
+ ret = mount("devpts", mntpoint, "devpts", MS_NOSUID | MS_NOEXEC,
+ "newinstance,ptmxmode=0666,mode=0620,gid=5");
+ if (ret < 0) {
+ fprintf(stderr, "Failed to mount devpts fs to \"%s\" in new "
+ "mount namespace: %s\n", mntpoint,
+ strerror(errno));
+ unlink(mntpoint);
+ return -1;
+ }
+
+ ret = snprintf(ptmx, sizeof(ptmx), "%s/ptmx", devpts);
+ if (ret < 0 || (size_t)ret >= sizeof(ptmx)) {
+ unlink(mntpoint);
+ return -1;
+ }
+
+ ret = do_tiocgptpeer(ptmx, mntpoint);
+ unlink(mntpoint);
+ if (ret < 0)
+ return -1;
+
+ return 0;
+}
+
+static int verify_ptmx_bind_mount(void)
+{
+ int ret;
+
+ ret = mount("/dev/pts/ptmx", "/dev/ptmx", NULL, MS_BIND, NULL);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to bind mount \"/dev/pts/ptmx\" to "
+ "\"/dev/ptmx\" mount namespace\n");
+ return -1;
+ }
+
+ ret = do_tiocgptpeer("/dev/ptmx", "/dev/pts/");
+ if (ret < 0)
+ return -1;
+
+ return 0;
+}
+
+static int verify_invalid_ptmx_bind_mount(void)
+{
+ int ret;
+ char mntpoint_fd;
+ char ptmx[] = P_tmpdir "/devpts_ptmx_XXXXXX";
+
+ mntpoint_fd = mkstemp(ptmx);
+ if (mntpoint_fd < 0) {
+ fprintf(stderr, "Failed to create temporary directory: %s\n",
+ strerror(errno));
+ return -1;
+ }
+
+ ret = mount("/dev/pts/ptmx", ptmx, NULL, MS_BIND, NULL);
+ close(mntpoint_fd);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to bind mount \"/dev/pts/ptmx\" to "
+ "\"%s\" mount namespace\n", ptmx);
+ return -1;
+ }
+
+ ret = do_tiocgptpeer(ptmx, "/dev/pts/");
+ if (ret == 0)
+ return -1;
+
+ return 0;
+}
+
+int main(int argc, char *argv[])
+{
+ int ret;
+
+ if (!isatty(STDIN_FILENO)) {
+ fprintf(stderr, "Standard input file desciptor is not attached "
+ "to a terminal. Skipping test\n");
+ exit(EXIT_FAILURE);
+ }
+
+ ret = unshare(CLONE_NEWNS);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to unshare mount namespace\n");
+ exit(EXIT_FAILURE);
+ }
+
+ ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to make \"/\" MS_PRIVATE in new mount "
+ "namespace\n");
+ exit(EXIT_FAILURE);
+ }
+
+ ret = verify_ptmx_bind_mount();
+ if (ret < 0)
+ exit(EXIT_FAILURE);
+
+ ret = verify_invalid_ptmx_bind_mount();
+ if (ret < 0)
+ exit(EXIT_FAILURE);
+
+ ret = verify_non_standard_devpts_mount();
+ if (ret < 0)
+ exit(EXIT_FAILURE);
+
+ exit(EXIT_SUCCESS);
+}
--
2.15.1