Kernel: Pass correct permission flags when opening files

Right now, permission flags passed to VFS::open() are effectively ignored, but
that is going to change.

* O_RDONLY is 0, but it's still nicer to pass it explicitly
* POSIX says that binding a Unix socket to a symlink shall fail with EADDRINUSE

Kernel/KSyms.cpp

@@ -182,7 +182,7 @@ void dump_backtrace()
 
 void load_ksyms()
 {
-    auto result = VFS::the().open("/res/kernel.map", 0, 0, VFS::the().root_custody());
+    auto result = VFS::the().open("/res/kernel.map", O_RDONLY, 0, VFS::the().root_custody());
     ASSERT(!result.is_error());
     auto description = result.value();
     auto buffer = description->read_entire_file();

Kernel/Net/LocalSocket.cpp

@@ -111,7 +111,7 @@ KResult LocalSocket::bind(const sockaddr* user_address, socklen_t address_size)
 
     mode_t mode = S_IFSOCK | (m_prebind_mode & 04777);
     UidAndGid owner { m_prebind_uid, m_prebind_gid };
-    auto result = VFS::the().open(path, O_CREAT | O_EXCL, mode, current->process().current_directory(), owner);
+    auto result = VFS::the().open(path, O_RDWR | O_CREAT | O_EXCL | O_NOFOLLOW_NOERROR, mode, current->process().current_directory(), owner);
     if (result.is_error()) {
         if (result.error() == -EEXIST)
             return KResult(-EADDRINUSE);
@@ -145,7 +145,7 @@ KResult LocalSocket::connect(FileDescription& description, const sockaddr* addre
     kprintf("%s(%u) LocalSocket{%p} connect(%s)\n", current->process().name().characters(), current->pid(), this, safe_address);
 #endif
 
-    auto description_or_error = VFS::the().open(safe_address, 0, 0, current->process().current_directory());
+    auto description_or_error = VFS::the().open(safe_address, O_RDWR, 0, current->process().current_directory());
     if (description_or_error.is_error())
         return KResult(-ECONNREFUSED);
 

Kernel/Process.cpp

@@ -4222,7 +4222,7 @@ int Process::sys$module_load(const char* user_path, size_t path_length)
     auto path = get_syscall_path_argument(user_path, path_length);
     if (path.is_error())
         return path.error();
-    auto description_or_error = VFS::the().open(path.value(), 0, 0, current_directory());
+    auto description_or_error = VFS::the().open(path.value(), O_RDONLY, 0, current_directory());
     if (description_or_error.is_error())
         return description_or_error.error();
     auto& description = description_or_error.value();

Tests/Kernel/bind-local-socket-to-symlink.cpp

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+int main(int, char**)
+{
+    constexpr const char* path = "/tmp/foo";
+    int rc = symlink("bar", path);
+    if (rc < 0) {
+        perror("symlink");
+        return 1;
+    }
+
+    int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (fd < 0) {
+        perror("socket");
+        return 1;
+    }
+
+    struct sockaddr_un addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.sun_family = AF_UNIX;
+    strncpy(addr.sun_path, path, sizeof(addr.sun_path) - 1);
+
+    rc = bind(fd, (struct sockaddr*)(&addr), sizeof(addr));
+    if (rc < 0 && errno == EADDRINUSE)
+        return 0;
+
+    return 1;
+}