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SubjectRe: [PATCH v3 3/3] selftests/seccomp: Test kernel catches garbage on SECCOMP_IOCTL_NOTIF_RECV
On Sat, Dec 28, 2019 at 10:24:51PM -0800, Sargun Dhillon wrote:
> Add a self-test to make sure that the kernel returns EINVAL, if any
> of the fields in seccomp_notif are set to non-null.
>
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> Suggested-by: Christian Brauner <christian.brauner@ubuntu.com>
> Cc: Kees Cook <keescook@chromium.org>
> ---
> tools/testing/selftests/seccomp/seccomp_bpf.c | 23 +++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index f53f14971bff..379391a7fa41 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -3601,6 +3601,29 @@ TEST(user_notification_continue)
> }
> }
>
> +TEST(user_notification_garbage)
> +{
> + /*
> + * intentionally set pid to a garbage value to make sure the kernel
> + * catches it
> + */
> + struct seccomp_notif req = {
> + .pid = 1,
> + };
> + int ret, listener;
> +
> + ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
> + ASSERT_EQ(0, ret) {
> + TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
> + }
> +
> + listener = user_trap_syscall(__NR_dup, SECCOMP_FILTER_FLAG_NEW_LISTENER);
> + ASSERT_GE(listener, 0);
> +
> + EXPECT_EQ(-1, ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req));
> + EXPECT_EQ(EINVAL, errno);

Does that even work if no dup() syscall has been made and trapped?
This looks like it would give you ENOENT...

If you want a simple solution just do:

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 6944b898bb53..4c73ae8679ea 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -3095,7 +3095,7 @@ TEST(user_notification_basic)
pid_t pid;
long ret;
int status, listener;
- struct seccomp_notif req = {};
+ struct seccomp_notif req;
struct seccomp_notif_resp resp = {};
struct pollfd pollfd;

@@ -3158,6 +3158,13 @@ TEST(user_notification_basic)
EXPECT_GT(poll(&pollfd, 1, -1), 0);
EXPECT_EQ(pollfd.revents, POLLIN);

+ /* Test that we can't pass garbage to the kernel. */
+ memset(&req, 0, sizeof(req));
+ req.pid = -1;
+ EXPECT_EQ(-1, ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req));
+ EXPECT_EQ(EINVAL, errno);
+
+ req.pid = 0;
EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);

pollfd.fd = listener

If you want a complete separate test then you can do:

TEST(user_notification_garbage_recv)
{
pid_t pid;
long ret;
int status, listener;
struct seccomp_notif req;
struct seccomp_notif_resp resp = {};
struct pollfd pollfd;
ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
ASSERT_EQ(0, ret) {
TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
}
listener = user_trap_syscall(__NR_getppid,
SECCOMP_FILTER_FLAG_NEW_LISTENER);
ASSERT_GE(listener, 0);

pid = fork();
ASSERT_GE(pid, 0);

if (pid == 0) {
ret = syscall(__NR_getppid);
exit(ret != USER_NOTIF_MAGIC);
}
pollfd.fd = listener;
pollfd.events = POLLIN | POLLOUT;
EXPECT_GT(poll(&pollfd, 1, -1), 0);
EXPECT_EQ(pollfd.revents, POLLIN);

memset(&req, 0, sizeof(req));
req.pid = -1;
EXPECT_EQ(-1, ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req));
EXPECT_EQ(EINVAL, errno);

req.pid = 0;
EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);

pollfd.fd = listener;
pollfd.events = POLLIN | POLLOUT;
EXPECT_GT(poll(&pollfd, 1, -1), 0);
EXPECT_EQ(pollfd.revents, POLLOUT);

EXPECT_EQ(req.data.nr, __NR_getppid);

memset(&resp, 0, sizeof(resp));
resp.id = req.id;
resp.error = 0;
resp.val = USER_NOTIF_MAGIC;
EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);

EXPECT_EQ(waitpid(pid, &status, 0), pid);
EXPECT_EQ(true, WIFEXITED(status));
EXPECT_EQ(0, WEXITSTATUS(status));
}
Christian

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