Fixes for seccomp_notify_ioctl uapi sanity

- Fix samples and selftests to zero passed-in buffer (Sargun Dhillon)
 - Enforce zeroed buffer checking (Sargun Dhillon)
 - Verify buffer sanity check in selftest (Sargun Dhillon)
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 Comment: Kees Cook <kees@outflux.net>
 
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Merge tag 'seccomp-v5.5-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull seccomp fixes from Kees Cook:
 "Fixes for seccomp_notify_ioctl uapi sanity from Sargun Dhillon.

  The bulk of this is fixing the surrounding samples and selftests so
  that seccomp can correctly validate the seccomp_notify_ioctl buffer as
  being initially zeroed.

  Summary:

   - Fix samples and selftests to zero passed-in buffer

   - Enforce zeroed buffer checking

   - Verify buffer sanity check in selftest"

* tag 'seccomp-v5.5-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  selftests/seccomp: Catch garbage on SECCOMP_IOCTL_NOTIF_RECV
  seccomp: Check that seccomp_notif is zeroed out by the user
  selftests/seccomp: Zero out seccomp_notif
  samples/seccomp: Zero out members based on seccomp_notif_sizes

kernel/seccomp.c

@@ -1026,6 +1026,13 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
 	struct seccomp_notif unotif;
 	ssize_t ret;
 
+	/* Verify that we're not given garbage to keep struct extensible. */
+	ret = check_zeroed_user(buf, sizeof(unotif));
+	if (ret < 0)
+		return ret;
+	if (!ret)
+		return -EINVAL;
+
 	memset(&unotif, 0, sizeof(unotif));
 
 	ret = down_interruptible(&filter->notif->request);

samples/seccomp/user-trap.c

@@ -298,14 +298,14 @@ int main(void)
 		req = malloc(sizes.seccomp_notif);
 		if (!req)
 			goto out_close;
-		memset(req, 0, sizeof(*req));
 
 		resp = malloc(sizes.seccomp_notif_resp);
 		if (!resp)
 			goto out_req;
-		memset(resp, 0, sizeof(*resp));
+		memset(resp, 0, sizes.seccomp_notif_resp);
 
 		while (1) {
+			memset(req, 0, sizes.seccomp_notif);
 			if (ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, req)) {
 				perror("ioctl recv");
 				goto out_resp;

tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -3158,7 +3158,18 @@ TEST(user_notification_basic)
 	EXPECT_GT(poll(&pollfd, 1, -1), 0);
 	EXPECT_EQ(pollfd.revents, POLLIN);
 
-	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	/* Test that we can't pass garbage to the kernel. */
+	memset(&req, 0, sizeof(req));
+	req.pid = -1;
+	errno = 0;
+	ret = ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req);
+	EXPECT_EQ(-1, ret);
+	EXPECT_EQ(EINVAL, errno);
+
+	if (ret) {
+		req.pid = 0;
+		EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
+	}
 
 	pollfd.fd = listener;
 	pollfd.events = POLLIN | POLLOUT;
@@ -3278,6 +3289,7 @@ TEST(user_notification_signal)
 
 	close(sk_pair[1]);
 
+	memset(&req, 0, sizeof(req));
 	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
 
 	EXPECT_EQ(kill(pid, SIGUSR1), 0);
@@ -3296,6 +3308,7 @@ TEST(user_notification_signal)
 	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), -1);
 	EXPECT_EQ(errno, ENOENT);
 
+	memset(&req, 0, sizeof(req));
 	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, &req), 0);
 
 	resp.id = req.id;