Assorted hardening issues flagged by kres (#42802)

src/basic/env-util.c

@@ -948,6 +948,8 @@ int replace_env_argv(
                         }
 
                         k += q;
+                        /* reallocarray() does not zero-initialize the grown tail, add NUL termination */
+                        n[k] = NULL;
                         continue;
                 }
 

src/shared/libfido2-util.c

@@ -622,6 +622,8 @@ static int fido2_use_hmac_hash_specific_token(
                 return log_error_errno(SYNTHETIC_ERRNO(EIO), "Failed to retrieve HMAC secret.");
 
         hmac_size = sym_fido_assert_hmac_secret_len(a, 0);
+        /* Should never be zero, sanity check */
+        assert(hmac_size > 0);
 
         hmac_copy = memdup(hmac, hmac_size);
         if (!hmac_copy)
@@ -1160,6 +1162,8 @@ int fido2_generate_hmac_hash(
                 return log_error_errno(SYNTHETIC_ERRNO(EIO), "Failed to retrieve HMAC secret.");
 
         secret_size = sym_fido_assert_hmac_secret_len(a, 0);
+        /* Should never be zero, sanity check */
+        assert(secret_size > 0);
 
         secret_copy = memdup(secret, secret_size);
         if (!secret_copy)

src/shared/ptyfwd.c

@@ -889,19 +889,16 @@ static int on_sigwinch_event(sd_event_source *e, const struct signalfd_siginfo *
 
 static int on_exit_event(sd_event_source *e, void *userdata) {
         PTYForward *f = ASSERT_PTR(userdata);
-        int r;
 
         assert(e);
         assert(e == f->exit_event_source);
 
-        if (!pty_forward_drain(f)) {
-                /* If not drained, try to drain the buffer. */
-                r = shovel_force(f);
-                if (r < 0)
-                        return r;
-        }
-
-        return pty_forward_done(f, 0);
+        /* The event loop is exiting while the forwarder is still active. Force a final synchronous drain of
+         * whatever is still buffered. shovel() may complete the drain and call pty_forward_done(), which
+         * can free f via the hangup handler, so we must not touch f afterwards, only propagate the return
+         * value, exactly like on_master_event() does. */
+        f->drain = true;
+        return shovel_force(f);
 }
 
 static int on_defer_event(sd_event_source *s, void *userdata) {

src/test/test-env-util.c

@@ -590,4 +590,28 @@ TEST(strv_env_get_merged) {
         ASSERT_TRUE(strv_equal(m, expected));
 }
 
+TEST(replace_env_argv_unterminated) {
+        /* A bare unset "$VAR" token expands to nothing and advances neither the write index nor writes a
+         * terminator, so the output strv must still be NUL-terminated when such a token leads or is the
+         * only word. */
+
+        _cleanup_strv_free_ char **a = NULL, **b = NULL, **c = NULL, **d = NULL;
+
+        /* Single bare unset variable: result must be a properly terminated empty strv. */
+        ASSERT_OK(replace_env_argv(STRV_MAKE("$THIS_IS_UNSET"), STRV_MAKE("FOO=BAR"), &a, NULL, NULL));
+        ASSERT_TRUE(strv_isempty(a));
+
+        /* Only unset variables. */
+        ASSERT_OK(replace_env_argv(STRV_MAKE("$THIS_IS_UNSET", "$ALSO_UNSET"), STRV_MAKE("FOO=BAR"), &b, NULL, NULL));
+        ASSERT_TRUE(strv_isempty(b));
+
+        /* Trailing bare unset variable after an expanded one. */
+        ASSERT_OK(replace_env_argv(STRV_MAKE("$FOO", "$THIS_IS_UNSET"), STRV_MAKE("FOO=BAR"), &c, NULL, NULL));
+        ASSERT_TRUE(strv_equal(c, STRV_MAKE("BAR")));
+
+        /* Trailing bare unset variable after a literal word. */
+        ASSERT_OK(replace_env_argv(STRV_MAKE("hello", "$THIS_IS_UNSET"), STRV_MAKE("FOO=BAR"), &d, NULL, NULL));
+        ASSERT_TRUE(strv_equal(d, STRV_MAKE("hello")));
+}
+
 DEFINE_TEST_MAIN(LOG_DEBUG);

test/units/TEST-74-AUX-UTILS.run.sh

@@ -314,3 +314,19 @@ fi
 
 # Tests whether intermediate disconnects corrupt us (modified testcase from https://github.com/systemd/systemd/issues/27204)
 assert_rc "37" timeout 300 systemd-run --unit=disconnecttest --wait --pipe --user -M testuser@.host bash -ec 'systemctl --user daemon-reexec; sleep 3; exit 37'
+
+# Trigger on_exit_event(): SIGINT makes systemd-run leave the event loop
+# while PTY forwarding is active. coproc gives us a pollable stdout and exec
+# makes $PTY_FWD_PID point at systemd-run
+coproc PTY_FWD { exec systemd-run --quiet --pty -- bash -c 'echo PTY_FORWARD_READY; exec sleep 60'; }
+PTY_FWD_PID_SAVED="$PTY_FWD_PID"
+read -r -t 30 -u "${PTY_FWD[0]}" PTY_FWD_LINE || true
+[[ "$PTY_FWD_LINE" == *PTY_FORWARD_READY* ]]
+kill -INT "$PTY_FWD_PID_SAVED"
+PTY_FWD_RC=0
+wait "$PTY_FWD_PID_SAVED" || PTY_FWD_RC=$?
+# ASan reports the UAF as systemd-run exiting non-zero.
+if [[ "$PTY_FWD_RC" != 0 ]]; then
+    echo "systemd-run --pty failed"
+    exit 1
+fi