Kernel: Make copy_to/from_user safe and remove unnecessary checks

Since the CPU already does almost all necessary validation steps
for us, we don't really need to attempt to do this. Doing it
ourselves doesn't really work very reliably, because we'd have to
account for other processors modifying virtual memory, and we'd
have to account for e.g. pages not being able to be allocated
due to insufficient resources.

So change the copy_to/from_user (and associated helper functions)
to use the new safe_memcpy, which will return whether it succeeded
or not. The only manual validation step needed (which the CPU
can't perform for us) is making sure the pointers provided by user
mode aren't pointing to kernel mappings.

To make it easier to read/write from/to either kernel or user mode
data add the UserOrKernelBuffer helper class, which will internally
either use copy_from/to_user or directly memcpy, or pass the data
through directly using a temporary buffer on the stack.

Last but not least we need to keep syscall params trivial as we
need to copy them from/to user mode using copy_from/to_user.

1 files changed, 72 insertions, 50 deletions

diff --git a/Kernel/Net/IPv4Socket.cpp b/Kernel/Net/IPv4Socket.cpp
index 7ddead3e15..c64c036c4d 100644
--- a/Kernel/Net/IPv4Socket.cpp
+++ b/Kernel/Net/IPv4Socket.cpp
@@ -105,7 +105,8 @@ KResult IPv4Socket::bind(Userspace<const sockaddr*> user_address, socklen_t addr
         return KResult(-EINVAL);
 
     sockaddr_in address;
-    copy_from_user(&address, user_address, sizeof(sockaddr_in));
+    if (!copy_from_user(&address, user_address, sizeof(sockaddr_in)))
+        return KResult(-EFAULT);
 
     if (address.sin_family != AF_INET)
         return KResult(-EINVAL);
@@ -144,18 +145,25 @@ KResult IPv4Socket::listen(size_t backlog)
     return protocol_listen();
 }
 
-KResult IPv4Socket::connect(FileDescription& description, const sockaddr* address, socklen_t address_size, ShouldBlock should_block)
+KResult IPv4Socket::connect(FileDescription& description, Userspace<const sockaddr*> address, socklen_t address_size, ShouldBlock should_block)
 {
     if (address_size != sizeof(sockaddr_in))
         return KResult(-EINVAL);
-    if (address->sa_family != AF_INET)
+    u16 sa_family_copy;
+    auto* user_address = reinterpret_cast<const sockaddr*>(address.unsafe_userspace_ptr());
+    if (!copy_from_user(&sa_family_copy, &user_address->sa_family, sizeof(u16)))
+        return KResult(-EFAULT);
+    if (sa_family_copy != AF_INET)
         return KResult(-EINVAL);
     if (m_role == Role::Connected)
         return KResult(-EISCONN);
 
-    auto& ia = *(const sockaddr_in*)address;
-    m_peer_address = IPv4Address((const u8*)&ia.sin_addr.s_addr);
-    m_peer_port = ntohs(ia.sin_port);
+    sockaddr_in safe_address;
+    if (!copy_from_user(&safe_address, (const sockaddr_in*)user_address, sizeof(sockaddr_in)))
+        return KResult(-EFAULT);
+
+    m_peer_address = IPv4Address((const u8*)&safe_address.sin_addr.s_addr);
+    m_peer_port = ntohs(safe_address.sin_port);
 
     return protocol_connect(description, should_block);
 }
@@ -193,7 +201,7 @@ int IPv4Socket::allocate_local_port_if_needed()
     return port;
 }
 
-KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const void* data, size_t data_length, int flags, Userspace<const sockaddr*> addr, socklen_t addr_length)
+KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const UserOrKernelBuffer& data, size_t data_length, int flags, Userspace<const sockaddr*> addr, socklen_t addr_length)
 {
     (void)flags;
     if (addr && addr_length != sizeof(sockaddr_in))
@@ -201,7 +209,7 @@ KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const void* data, size_t
 
     if (addr) {
         sockaddr_in ia;
-        if (!Process::current()->validate_read_and_copy_typed(&ia, Userspace<const sockaddr_in*>(addr.ptr())))
+        if (!copy_from_user(&ia, Userspace<const sockaddr_in*>(addr.ptr())))
             return KResult(-EFAULT);
 
         if (ia.sin_family != AF_INET) {
@@ -229,7 +237,9 @@ KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const void* data, size_t
 #endif
 
     if (type() == SOCK_RAW) {
-        routing_decision.adapter->send_ipv4(routing_decision.next_hop, m_peer_address, (IPv4Protocol)protocol(), { (const u8*)data, data_length }, m_ttl);
+        int err = routing_decision.adapter->send_ipv4(routing_decision.next_hop, m_peer_address, (IPv4Protocol)protocol(), data, data_length, m_ttl);
+        if (err < 0)
+            return KResult(err);
         return data_length;
     }
 
@@ -239,7 +249,7 @@ KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const void* data, size_t
     return nsent_or_error;
 }
 
-KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description, void* buffer, size_t buffer_length, int, Userspace<sockaddr*>, Userspace<socklen_t*>)
+KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description, UserOrKernelBuffer& buffer, size_t buffer_length, int, Userspace<sockaddr*>, Userspace<socklen_t*>)
 {
     Locker locker(lock());
     if (m_receive_buffer.is_empty()) {
@@ -262,7 +272,7 @@ KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description
     }
 
     ASSERT(!m_receive_buffer.is_empty());
-    int nreceived = m_receive_buffer.read((u8*)buffer, buffer_length);
+    int nreceived = m_receive_buffer.read(buffer, buffer_length);
     if (nreceived > 0)
         Thread::current()->did_ipv4_socket_read((size_t)nreceived);
 
@@ -270,7 +280,7 @@ KResultOr<size_t> IPv4Socket::receive_byte_buffered(FileDescription& description
     return nreceived;
 }
 
-KResultOr<size_t> IPv4Socket::receive_packet_buffered(FileDescription& description, void* buffer, size_t buffer_length, int flags, Userspace<sockaddr*> addr, Userspace<socklen_t*> addr_length)
+KResultOr<size_t> IPv4Socket::receive_packet_buffered(FileDescription& description, UserOrKernelBuffer& buffer, size_t buffer_length, int flags, Userspace<sockaddr*> addr, Userspace<socklen_t*> addr_length)
 {
     Locker locker(lock());
     ReceivedPacket packet;
@@ -330,27 +340,30 @@ KResultOr<size_t> IPv4Socket::receive_packet_buffered(FileDescription& descripti
         out_addr.sin_port = htons(packet.peer_port);
         out_addr.sin_family = AF_INET;
         Userspace<sockaddr_in*> dest_addr = addr.ptr();
-        copy_to_user(dest_addr, &out_addr);
+        if (!copy_to_user(dest_addr, &out_addr))
+            return KResult(-EFAULT);
 
         socklen_t out_length = sizeof(sockaddr_in);
         ASSERT(addr_length);
-        copy_to_user(addr_length, &out_length);
+        if (!copy_to_user(addr_length, &out_length))
+            return KResult(-EFAULT);
     }
 
     if (type() == SOCK_RAW) {
         size_t bytes_written = min((size_t) ipv4_packet.payload_size(), buffer_length);
-        memcpy(buffer, ipv4_packet.payload(), bytes_written);
+        if (!buffer.write(ipv4_packet.payload(), bytes_written))
+            return KResult(-EFAULT);
         return bytes_written;
     }
 
     return protocol_receive(packet.data.value(), buffer, buffer_length, flags);
 }
 
-KResultOr<size_t> IPv4Socket::recvfrom(FileDescription& description, void* buffer, size_t buffer_length, int flags, Userspace<sockaddr*> user_addr, Userspace<socklen_t*> user_addr_length)
+KResultOr<size_t> IPv4Socket::recvfrom(FileDescription& description, UserOrKernelBuffer& buffer, size_t buffer_length, int flags, Userspace<sockaddr*> user_addr, Userspace<socklen_t*> user_addr_length)
 {
     if (user_addr_length) {
         socklen_t addr_length;
-        if (!Process::current()->validate_read_and_copy_typed(&addr_length, user_addr_length))
+        if (!copy_from_user(&addr_length, user_addr_length.unsafe_userspace_ptr()))
             return KResult(-EFAULT);
         if (addr_length < sizeof(sockaddr_in))
             return KResult(-EINVAL);
@@ -387,10 +400,13 @@ bool IPv4Socket::did_receive(const IPv4Address& source_address, u16 source_port,
             ASSERT(m_can_read);
             return false;
         }
-        auto nreceived_or_error = protocol_receive(packet, m_scratch_buffer.value().data(), m_scratch_buffer.value().size(), 0);
+        auto scratch_buffer = UserOrKernelBuffer::for_kernel_buffer(m_scratch_buffer.value().data());
+        auto nreceived_or_error = protocol_receive(packet, scratch_buffer, m_scratch_buffer.value().size(), 0);
         if (nreceived_or_error.is_error())
             return false;
-        m_receive_buffer.write(m_scratch_buffer.value().data(), nreceived_or_error.value());
+        ssize_t nwritten = m_receive_buffer.write(scratch_buffer, nreceived_or_error.value());
+        if (nwritten < 0)
+            return false;
         m_can_read = !m_receive_buffer.is_empty();
     } else {
         if (m_receive_queue.size() > 2000) {
@@ -452,7 +468,7 @@ KResult IPv4Socket::setsockopt(int level, int option, Userspace<const void*> use
         if (user_value_size < sizeof(int))
             return KResult(-EINVAL);
         int value;
-        if (!Process::current()->validate_read_and_copy_typed(&value, static_ptr_cast<const int*>(user_value)))
+        if (!copy_from_user(&value, static_ptr_cast<const int*>(user_value)))
             return KResult(-EFAULT);
         if (value < 0 || value > 255)
             return KResult(-EINVAL);
@@ -470,16 +486,18 @@ KResult IPv4Socket::getsockopt(FileDescription& description, int level, int opti
         return Socket::getsockopt(description, level, option, value, value_size);
 
     socklen_t size;
-    if (!Process::current()->validate_read_and_copy_typed(&size, value_size))
+    if (!copy_from_user(&size, value_size.unsafe_userspace_ptr()))
         return KResult(-EFAULT);
 
     switch (option) {
     case IP_TTL:
         if (size < sizeof(int))
             return KResult(-EINVAL);
-        copy_to_user(static_ptr_cast<int*>(value), (int*)&m_ttl);
+        if (!copy_to_user(static_ptr_cast<int*>(value), (int*)&m_ttl))
+            return KResult(-EFAULT);
         size = sizeof(int);
-        copy_to_user(value_size, &size);
+        if (!copy_to_user(value_size, &size))
+            return KResult(-EFAULT);
         return KSuccess;
     default:
         return KResult(-ENOPROTOOPT);
@@ -493,15 +511,15 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, FlatPtr arg)
     SmapDisabler disabler;
 
     auto ioctl_route = [request, arg]() {
-        auto* route = (rtentry*)arg;
-        if (!Process::current()->validate_read_typed(route))
+        rtentry route;
+        if (!copy_from_user(&route, (rtentry*)arg))
             return -EFAULT;
 
-        char namebuf[IFNAMSIZ + 1];
-        memcpy(namebuf, route->rt_dev, IFNAMSIZ);
-        namebuf[sizeof(namebuf) - 1] = '\0';
+        auto copied_ifname = copy_string_from_user(route.rt_dev, IFNAMSIZ);
+        if (copied_ifname.is_null())
+            return -EFAULT;
 
-        auto adapter = NetworkAdapter::lookup_by_name(namebuf);
+        auto adapter = NetworkAdapter::lookup_by_name(copied_ifname);
         if (!adapter)
             return -ENODEV;
 
@@ -509,11 +527,11 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, FlatPtr arg)
         case SIOCADDRT:
             if (!Process::current()->is_superuser())
                 return -EPERM;
-            if (route->rt_gateway.sa_family != AF_INET)
+            if (route.rt_gateway.sa_family != AF_INET)
                 return -EAFNOSUPPORT;
-            if ((route->rt_flags & (RTF_UP | RTF_GATEWAY)) != (RTF_UP | RTF_GATEWAY))
+            if ((route.rt_flags & (RTF_UP | RTF_GATEWAY)) != (RTF_UP | RTF_GATEWAY))
                 return -EINVAL; // FIXME: Find the correct value to return
-            adapter->set_ipv4_gateway(IPv4Address(((sockaddr_in&)route->rt_gateway).sin_addr.s_addr));
+            adapter->set_ipv4_gateway(IPv4Address(((sockaddr_in&)route.rt_gateway).sin_addr.s_addr));
             return 0;
 
         case SIOCDELRT:
@@ -525,12 +543,13 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, FlatPtr arg)
     };
 
     auto ioctl_interface = [request, arg]() {
-        auto* ifr = (ifreq*)arg;
-        if (!Process::current()->validate_read_typed(ifr))
+        ifreq* user_ifr = (ifreq*)arg;
+        ifreq ifr;
+        if (!copy_from_user(&ifr, user_ifr))
             return -EFAULT;
 
         char namebuf[IFNAMSIZ + 1];
-        memcpy(namebuf, ifr->ifr_name, IFNAMSIZ);
+        memcpy(namebuf, ifr.ifr_name, IFNAMSIZ);
         namebuf[sizeof(namebuf) - 1] = '\0';
 
         auto adapter = NetworkAdapter::lookup_by_name(namebuf);
@@ -541,36 +560,39 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, FlatPtr arg)
         case SIOCSIFADDR:
             if (!Process::current()->is_superuser())
                 return -EPERM;
-            if (ifr->ifr_addr.sa_family != AF_INET)
+            if (ifr.ifr_addr.sa_family != AF_INET)
                 return -EAFNOSUPPORT;
-            adapter->set_ipv4_address(IPv4Address(((sockaddr_in&)ifr->ifr_addr).sin_addr.s_addr));
+            adapter->set_ipv4_address(IPv4Address(((sockaddr_in&)ifr.ifr_addr).sin_addr.s_addr));
             return 0;
 
         case SIOCSIFNETMASK:
             if (!Process::current()->is_superuser())
                 return -EPERM;
-            if (ifr->ifr_addr.sa_family != AF_INET)
+            if (ifr.ifr_addr.sa_family != AF_INET)
                 return -EAFNOSUPPORT;
-            adapter->set_ipv4_netmask(IPv4Address(((sockaddr_in&)ifr->ifr_netmask).sin_addr.s_addr));
+            adapter->set_ipv4_netmask(IPv4Address(((sockaddr_in&)ifr.ifr_netmask).sin_addr.s_addr));
             return 0;
 
-        case SIOCGIFADDR:
-            if (!Process::current()->validate_write_typed(ifr))
+        case SIOCGIFADDR: {
+            u16 sa_family = AF_INET;
+            if (!copy_to_user(&user_ifr->ifr_addr.sa_family, &sa_family))
+                return -EFAULT;
+            auto ip4_addr = adapter->ipv4_address().to_u32();
+            if (!copy_to_user(&((sockaddr_in&)user_ifr->ifr_addr).sin_addr.s_addr, &ip4_addr, sizeof(ip4_addr)))
                 return -EFAULT;
-            ifr->ifr_addr.sa_family = AF_INET;
-            ((sockaddr_in&)ifr->ifr_addr).sin_addr.s_addr = adapter->ipv4_address().to_u32();
             return 0;
+        }
 
-        case SIOCGIFHWADDR:
-            if (!Process::current()->validate_write_typed(ifr))
+        case SIOCGIFHWADDR: {
+            u16 sa_family = AF_INET;
+            if (!copy_to_user(&user_ifr->ifr_hwaddr.sa_family, &sa_family))
+                return -EFAULT;
+            auto mac_address = adapter->mac_address();
+            if (!copy_to_user(ifr.ifr_hwaddr.sa_data, &mac_address, sizeof(MACAddress)))
                 return -EFAULT;
-            ifr->ifr_hwaddr.sa_family = AF_INET;
-            {
-                auto mac_address = adapter->mac_address();
-                memcpy(ifr->ifr_hwaddr.sa_data, &mac_address, sizeof(MACAddress));
-            }
             return 0;
         }
+        }
 
         return -EINVAL;
     };