[PATCH v8 7/9] selftests/landlock: Test FD passing from a Landlock-restricted to an unrestricted process
Mickaël Salaün
mic at digikod.net
Wed Oct 5 18:57:12 UTC 2022
Thanks for this refactoring.
We need a shorter subject though. ;)
On 01/10/2022 17:49, Günther Noack wrote:
> A file descriptor created in a restricted process carries Landlock
> restrictions with it which will apply even if the same opened file is
> used from an unrestricted process.
>
> This change extracts suitable FD-passing helpers from base_test.c and
> moves them to common.h. We use the fixture variants from the ftruncate
> fixture to exercise the same scenarios as in the open_and_ftruncate
> test, but doing the Landlock restriction and open() in a different
> process than the ftruncate() call.
>
> Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
> ---
> tools/testing/selftests/landlock/base_test.c | 36 +----------
> tools/testing/selftests/landlock/common.h | 67 ++++++++++++++++++++
> tools/testing/selftests/landlock/fs_test.c | 62 ++++++++++++++++++
> 3 files changed, 132 insertions(+), 33 deletions(-)
>
> diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
> index 72cdae277b02..6d1b6eedb432 100644
> --- a/tools/testing/selftests/landlock/base_test.c
> +++ b/tools/testing/selftests/landlock/base_test.c
> @@ -263,23 +263,6 @@ TEST(ruleset_fd_transfer)
> .allowed_access = LANDLOCK_ACCESS_FS_READ_DIR,
> };
> int ruleset_fd_tx, dir_fd;
> - union {
> - /* Aligned ancillary data buffer. */
> - char buf[CMSG_SPACE(sizeof(ruleset_fd_tx))];
> - struct cmsghdr _align;
> - } cmsg_tx = {};
> - char data_tx = '.';
> - struct iovec io = {
> - .iov_base = &data_tx,
> - .iov_len = sizeof(data_tx),
> - };
> - struct msghdr msg = {
> - .msg_iov = &io,
> - .msg_iovlen = 1,
> - .msg_control = &cmsg_tx.buf,
> - .msg_controllen = sizeof(cmsg_tx.buf),
> - };
> - struct cmsghdr *cmsg;
> int socket_fds[2];
> pid_t child;
> int status;
> @@ -298,33 +281,20 @@ TEST(ruleset_fd_transfer)
> &path_beneath_attr, 0));
> ASSERT_EQ(0, close(path_beneath_attr.parent_fd));
>
> - cmsg = CMSG_FIRSTHDR(&msg);
> - ASSERT_NE(NULL, cmsg);
> - cmsg->cmsg_len = CMSG_LEN(sizeof(ruleset_fd_tx));
> - cmsg->cmsg_level = SOL_SOCKET;
> - cmsg->cmsg_type = SCM_RIGHTS;
> - memcpy(CMSG_DATA(cmsg), &ruleset_fd_tx, sizeof(ruleset_fd_tx));
> -
> /* Sends the ruleset FD over a socketpair and then close it. */
> ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0,
> socket_fds));
> - ASSERT_EQ(sizeof(data_tx), sendmsg(socket_fds[0], &msg, 0));
> + ASSERT_EQ(0, send_fd(socket_fds[0], ruleset_fd_tx));
> ASSERT_EQ(0, close(socket_fds[0]));
> ASSERT_EQ(0, close(ruleset_fd_tx));
>
> child = fork();
> ASSERT_LE(0, child);
> if (child == 0) {
> - int ruleset_fd_rx;
> + int ruleset_fd_rx = recv_fd(socket_fds[1]);
We can now make it const.
>
> - *(char *)msg.msg_iov->iov_base = '\0';
> - ASSERT_EQ(sizeof(data_tx),
> - recvmsg(socket_fds[1], &msg, MSG_CMSG_CLOEXEC));
> - ASSERT_EQ('.', *(char *)msg.msg_iov->iov_base);
> + ASSERT_LE(0, ruleset_fd_rx);
> ASSERT_EQ(0, close(socket_fds[1]));
> - cmsg = CMSG_FIRSTHDR(&msg);
> - ASSERT_EQ(cmsg->cmsg_len, CMSG_LEN(sizeof(ruleset_fd_tx)));
> - memcpy(&ruleset_fd_rx, CMSG_DATA(cmsg), sizeof(ruleset_fd_tx));
>
> /* Enforces the received ruleset on the child. */
> ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
> diff --git a/tools/testing/selftests/landlock/common.h b/tools/testing/selftests/landlock/common.h
> index 7d34592471db..15149d34e43b 100644
> --- a/tools/testing/selftests/landlock/common.h
> +++ b/tools/testing/selftests/landlock/common.h
> @@ -10,6 +10,7 @@
> #include <errno.h>
> #include <linux/landlock.h>
> #include <sys/capability.h>
> +#include <sys/socket.h>
> #include <sys/syscall.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> @@ -189,3 +190,69 @@ static void __maybe_unused clear_cap(struct __test_metadata *const _metadata,
> {
> _effective_cap(_metadata, caps, CAP_CLEAR);
> }
> +
> +/* Receives an FD from a UNIX socket. Returns the received FD, -1 on error. */
> +static int __maybe_unused recv_fd(int usock)
> +{
> + int fd_rx;
> + union {
> + /* Aligned ancillary data buffer. */
> + char buf[CMSG_SPACE(sizeof(fd_rx))];
> + struct cmsghdr _align;
> + } cmsg_rx = {};
> + char data = '\0';
> + struct iovec io = {
> + .iov_base = &data,
> + .iov_len = sizeof(data),
> + };
> + struct msghdr msg = {
> + .msg_iov = &io,
> + .msg_iovlen = 1,
> + .msg_control = &cmsg_rx.buf,
> + .msg_controllen = sizeof(cmsg_rx.buf),
> + };
> + struct cmsghdr *cmsg;
> + int res;
> +
> + res = recvmsg(usock, &msg, MSG_CMSG_CLOEXEC);
> + if (res < 0)
> + return -1;
It could be useful to return -errno for recv_fd() and send_fd(), and
update the description accordingly. That would enable to quickly know
the error with the ASSERT_*() calls.
> +
> + cmsg = CMSG_FIRSTHDR(&msg);
> + if (cmsg->cmsg_len != CMSG_LEN(sizeof(fd_rx)))
> + return -1;
> +
> + memcpy(&fd_rx, CMSG_DATA(cmsg), sizeof(fd_rx));
> + return fd_rx;
> +}
> +
> +/* Sends an FD on a UNIX socket. Returns 0 on success or -1 on error. */
> +static int __maybe_unused send_fd(int usock, int fd_tx)
> +{
> + union {
> + /* Aligned ancillary data buffer. */
> + char buf[CMSG_SPACE(sizeof(fd_tx))];
> + struct cmsghdr _align;
> + } cmsg_tx = {};
> + char data_tx = '.';
> + struct iovec io = {
> + .iov_base = &data_tx,
> + .iov_len = sizeof(data_tx),
> + };
> + struct msghdr msg = {
> + .msg_iov = &io,
> + .msg_iovlen = 1,
> + .msg_control = &cmsg_tx.buf,
> + .msg_controllen = sizeof(cmsg_tx.buf),
> + };
> + struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
> +
> + cmsg->cmsg_len = CMSG_LEN(sizeof(fd_tx));
> + cmsg->cmsg_level = SOL_SOCKET;
> + cmsg->cmsg_type = SCM_RIGHTS;
> + memcpy(CMSG_DATA(cmsg), &fd_tx, sizeof(fd_tx));
> +
> + if (sendmsg(usock, &msg, 0) < 0)
> + return -1;
> + return 0;
> +}
> diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
> index 308f6f36e8c0..93ed80a25a74 100644
> --- a/tools/testing/selftests/landlock/fs_test.c
> +++ b/tools/testing/selftests/landlock/fs_test.c
> @@ -3541,6 +3541,68 @@ TEST_F_FORK(ftruncate, open_and_ftruncate)
> }
> }
>
> +TEST_F_FORK(ftruncate, open_and_ftruncate_in_different_processes)
> +{
> + int child, fd, status;
> + int socket_fds[2];
> +
> + ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0,
> + socket_fds));
> +
> + child = fork();
> + ASSERT_LE(0, child);
> + if (child == 0) {
> + /*
> + * Enable Landlock in the child process, open a file descriptor
"Enables"…
> + * where truncation is forbidden and send it to the
> + * non-landlocked parent process.
> + */
> + const char *const path = file1_s1d1;
> + const struct rule rules[] = {
> + {
> + .path = path,
> + .access = variant->permitted,
> + },
> + {},
> + };
> + int fd, ruleset_fd;
> +
> + /* Enable Landlock. */
This comment is not necessary.
> + ruleset_fd = create_ruleset(_metadata, variant->handled, rules);
> + ASSERT_LE(0, ruleset_fd);
> + enforce_ruleset(_metadata, ruleset_fd);
> + ASSERT_EQ(0, close(ruleset_fd));
> +
> + fd = open(path, O_WRONLY);
> + ASSERT_EQ(variant->expected_open_result, (fd < 0 ? errno : 0));
> +
> + if (fd >= 0) {
> + ASSERT_EQ(0, send_fd(socket_fds[0], fd));
> + ASSERT_EQ(0, close(fd));
> + }
> +
> + ASSERT_EQ(0, close(socket_fds[0]));
> +
> + _exit(_metadata->passed ? EXIT_SUCCESS : EXIT_FAILURE);
You might want to add a "return" here to help the compiler (and the reader).
> + }
> +
> + if (variant->expected_open_result == 0) {
> + fd = recv_fd(socket_fds[1]);
> + ASSERT_LE(0, fd);
> +
> + EXPECT_EQ(variant->expected_ftruncate_result,
> + test_ftruncate(fd));
> + ASSERT_EQ(0, close(fd));
> + }
> +
> + ASSERT_EQ(child, waitpid(child, &status, 0));
> + ASSERT_EQ(1, WIFEXITED(status));
> + ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
> +
> + ASSERT_EQ(0, close(socket_fds[0]));
> + ASSERT_EQ(0, close(socket_fds[1]));
> +}
> +
> /* clang-format off */
> FIXTURE(layout1_bind) {};
> /* clang-format on */
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