Userland: Add test for file SUID+SGID bits stripped when modified

Author: https://github.com/bcoles
Commit: https://github.com/SerenityOS/serenity/commit/549786e89a9
Pull-request: https://github.com/SerenityOS/serenity/pull/4046

Userland/Tests/Kernel/filesystem-strips-file-suid-sgid-bits-when-modified.cpp

@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+static void test_change_file_contents()
+{
+    const char* path = "suid";
+
+    int fd = open(path, O_CREAT | O_RDWR, 06755);
+    assert(fd != -1);
+    ftruncate(fd, 0);
+
+    char buffer[8];
+    memset(&buffer, 0, sizeof(buffer));
+    write(fd, buffer, sizeof(buffer));
+
+    struct stat s;
+    assert(fstat(fd, &s) != -1);
+    close(fd);
+
+    assert(s.st_mode & ~S_ISUID);
+    assert(s.st_mode & ~S_ISGID);
+
+    unlink(path);
+}
+
+static void test_change_file_ownership()
+{
+    const char* path = "suid";
+
+    int fd = open(path, O_CREAT | O_RDWR, 06755);
+    assert(fd != -1);
+    ftruncate(fd, 0);
+
+    fchown(fd, getuid(), getgid());
+
+    struct stat s;
+    assert(fstat(fd, &s) != -1);
+    close(fd);
+
+    assert(s.st_mode & ~S_ISUID);
+    assert(s.st_mode & ~S_ISGID);
+
+    unlink(path);
+}
+
+static void test_change_file_permissions()
+{
+    const char* path = "suid";
+
+    int fd = open(path, O_CREAT | O_RDWR, 06755);
+    assert(fd != -1);
+    ftruncate(fd, 0);
+
+    fchmod(fd, 0755);
+
+    struct stat s;
+    assert(fstat(fd, &s) != -1);
+    close(fd);
+
+    assert(s.st_mode & ~S_ISUID);
+    assert(s.st_mode & ~S_ISGID);
+
+    unlink(path);
+}
+
+int main()
+{
+#define RUNTEST(x)                      \
+    {                                   \
+        printf("Running " #x " ...\n"); \
+        x();                            \
+        printf("Success!\n");           \
+    }
+    RUNTEST(test_change_file_contents);
+    RUNTEST(test_change_file_ownership);
+    RUNTEST(test_change_file_permissions);
+    printf("PASS\n");
+
+    return 0;
+}