OvmfPkg/VirtioFsDxe: handle the volume label in EFI_FILE_PROTOCOL.SetInfo

The least complicated third of EFI_FILE_PROTOCOL.SetInfo() is to handle
the EFI_FILE_SYSTEM_INFO and EFI_FILE_SYSTEM_VOLUME_LABEL setting
requests. Both of those can only change the volume label -- which the
Virtio Filesystem device does not support.

Verify the input for well-formedness, and report success only if the
volume label is being set to its current value.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3097
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201216211125.19496-41-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/VirtioFsDxe/SimpleFsSetInfo.c

@@ -6,8 +6,220 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
+#include <Guid/FileSystemInfo.h>            // gEfiFileSystemInfoGuid
+#include <Guid/FileSystemVolumeLabelInfo.h> // gEfiFileSystemVolumeLabelInfo...
+#include <Library/BaseLib.h>                // StrCmp()
+#include <Library/BaseMemoryLib.h>          // CompareGuid()
+
 #include "VirtioFsDxe.h"
 
+/**
+  Validate a buffer that the EFI_FILE_PROTOCOL.SetInfo() caller passes in for a
+  particular InformationType GUID.
+
+  The structure to be validated is supposed to end with a variable-length,
+  NUL-terminated CHAR16 Name string.
+
+  @param[in] SizeByProtocolCaller  The BufferSize parameter as provided by the
+                                   EFI_FILE_PROTOCOL.SetInfo() caller.
+
+  @param[in] MinimumStructSize     The minimum structure size that is required
+                                   for the given InformationType GUID,
+                                   including a single CHAR16 element from the
+                                   trailing Name field.
+
+  @param[in] IsSizeByInfoPresent   TRUE if and only if the expected structure
+                                   starts with a UINT64 Size field that reports
+                                   the actual structure size.
+
+  @param[in] Buffer                The Buffer parameter as provided by the
+                                   EFI_FILE_PROTOCOL.SetInfo() caller.
+
+  @retval EFI_SUCCESS            Validation successful, Buffer is well-formed.
+
+  @retval EFI_BAD_BUFFER_SIZE    The EFI_FILE_PROTOCOL.SetInfo()
+                                 caller provided a BufferSize that is smaller
+                                 than the minimum structure size required for
+                                 the given InformationType GUID.
+
+  @retval EFI_INVALID_PARAMETER  IsSizeByInfoPresent is TRUE, and the leading
+                                 UINT64 Size field does not match the
+                                 EFI_FILE_PROTOCOL.SetInfo() caller-provided
+                                 BufferSize.
+
+  @retval EFI_INVALID_PARAMETER  The trailing Name field does not consist of a
+                                 whole multiple of CHAR16 elements.
+
+  @retval EFI_INVALID_PARAMETER  The trailing Name field is not NUL-terminated.
+**/
+STATIC
+EFI_STATUS
+ValidateInfoStructure (
+  IN UINTN   SizeByProtocolCaller,
+  IN UINTN   MinimumStructSize,
+  IN BOOLEAN IsSizeByInfoPresent,
+  IN VOID    *Buffer
+  )
+{
+  UINTN  NameFieldByteOffset;
+  UINTN  NameFieldBytes;
+  UINTN  NameFieldChar16s;
+  CHAR16 *NameField;
+
+  //
+  // Make sure the internal function asking for validation passes in sane
+  // values.
+  //
+  ASSERT (MinimumStructSize >= sizeof (CHAR16));
+  NameFieldByteOffset = MinimumStructSize - sizeof (CHAR16);
+
+  if (IsSizeByInfoPresent) {
+    ASSERT (MinimumStructSize >= sizeof (UINT64) + sizeof (CHAR16));
+    ASSERT (NameFieldByteOffset >= sizeof (UINT64));
+  }
+
+  //
+  // Check whether the protocol caller provided enough bytes for the minimum
+  // size of this info structure.
+  //
+  if (SizeByProtocolCaller < MinimumStructSize) {
+    return EFI_BAD_BUFFER_SIZE;
+  }
+
+  //
+  // If the info structure starts with a UINT64 Size field, check if that
+  // agrees with the protocol caller-provided size.
+  //
+  if (IsSizeByInfoPresent) {
+    UINT64 *SizeByInfo;
+
+    SizeByInfo = Buffer;
+    if (*SizeByInfo != SizeByProtocolCaller) {
+      return EFI_INVALID_PARAMETER;
+    }
+  }
+
+  //
+  // The CHAR16 Name field at the end of the structure must have an even number
+  // of bytes.
+  //
+  // The subtraction below cannot underflow, and yields at least
+  // sizeof(CHAR16).
+  //
+  ASSERT (SizeByProtocolCaller >= NameFieldByteOffset);
+  NameFieldBytes = SizeByProtocolCaller - NameFieldByteOffset;
+  ASSERT (NameFieldBytes >= sizeof (CHAR16));
+  if (NameFieldBytes % sizeof (CHAR16) != 0) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  //
+  // The CHAR16 Name field at the end of the structure must be NUL-terminated.
+  //
+  NameFieldChar16s = NameFieldBytes / sizeof (CHAR16);
+  ASSERT (NameFieldChar16s >= 1);
+
+  NameField = (CHAR16 *)((UINT8 *)Buffer + NameFieldByteOffset);
+  if (NameField[NameFieldChar16s - 1] != L'\0') {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  return EFI_SUCCESS;
+}
+
+/**
+  Process an EFI_FILE_SYSTEM_INFO setting request.
+**/
+STATIC
+EFI_STATUS
+SetFileSystemInfo (
+  IN EFI_FILE_PROTOCOL *This,
+  IN UINTN             BufferSize,
+  IN VOID              *Buffer
+  )
+{
+  VIRTIO_FS_FILE       *VirtioFsFile;
+  VIRTIO_FS            *VirtioFs;
+  EFI_STATUS           Status;
+  EFI_FILE_SYSTEM_INFO *FileSystemInfo;
+
+  VirtioFsFile = VIRTIO_FS_FILE_FROM_SIMPLE_FILE (This);
+  VirtioFs     = VirtioFsFile->OwnerFs;
+
+  //
+  // Validate if Buffer passes as EFI_FILE_SYSTEM_INFO.
+  //
+  Status = ValidateInfoStructure (
+             BufferSize,                       // SizeByProtocolCaller
+             OFFSET_OF (EFI_FILE_SYSTEM_INFO,
+               VolumeLabel) + sizeof (CHAR16), // MinimumStructSize
+             TRUE,                             // IsSizeByInfoPresent
+             Buffer
+             );
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+  FileSystemInfo = Buffer;
+
+  //
+  // EFI_FILE_SYSTEM_INFO fields other than VolumeLabel cannot be changed, per
+  // spec.
+  //
+  // If the label is being changed to its current value, report success;
+  // otherwise, reject the request, as the Virtio Filesystem device does not
+  // support changing the label.
+  //
+  if (StrCmp (FileSystemInfo->VolumeLabel, VirtioFs->Label) == 0) {
+    return EFI_SUCCESS;
+  }
+  return EFI_WRITE_PROTECTED;
+}
+
+/**
+  Process an EFI_FILE_SYSTEM_VOLUME_LABEL setting request.
+**/
+STATIC
+EFI_STATUS
+SetFileSystemVolumeLabelInfo (
+  IN EFI_FILE_PROTOCOL *This,
+  IN UINTN             BufferSize,
+  IN VOID              *Buffer
+  )
+{
+  VIRTIO_FS_FILE               *VirtioFsFile;
+  VIRTIO_FS                    *VirtioFs;
+  EFI_STATUS                   Status;
+  EFI_FILE_SYSTEM_VOLUME_LABEL *FileSystemVolumeLabel;
+
+  VirtioFsFile = VIRTIO_FS_FILE_FROM_SIMPLE_FILE (This);
+  VirtioFs     = VirtioFsFile->OwnerFs;
+
+  //
+  // Validate if Buffer passes as EFI_FILE_SYSTEM_VOLUME_LABEL.
+  //
+  Status = ValidateInfoStructure (
+             BufferSize,                              // SizeByProtocolCaller
+             OFFSET_OF (EFI_FILE_SYSTEM_VOLUME_LABEL,
+               VolumeLabel) + sizeof (CHAR16),        // MinimumStructSize
+             FALSE,                                   // IsSizeByInfoPresent
+             Buffer
+             );
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+  FileSystemVolumeLabel = Buffer;
+
+  //
+  // If the label is being changed to its current value, report success;
+  // otherwise, reject the request, as the Virtio Filesystem device does not
+  // support changing the label.
+  //
+  if (StrCmp (FileSystemVolumeLabel->VolumeLabel, VirtioFs->Label) == 0) {
+    return EFI_SUCCESS;
+  }
+  return EFI_WRITE_PROTECTED;
+}
+
 EFI_STATUS
 EFIAPI
 VirtioFsSimpleFileSetInfo (
@@ -17,5 +229,17 @@ VirtioFsSimpleFileSetInfo (
   IN VOID              *Buffer
   )
 {
-  return EFI_NO_MEDIA;
+  if (CompareGuid (InformationType, &gEfiFileInfoGuid)) {
+    return EFI_UNSUPPORTED;
+  }
+
+  if (CompareGuid (InformationType, &gEfiFileSystemInfoGuid)) {
+    return SetFileSystemInfo (This, BufferSize, Buffer);
+  }
+
+  if (CompareGuid (InformationType, &gEfiFileSystemVolumeLabelInfoIdGuid)) {
+    return SetFileSystemVolumeLabelInfo (This, BufferSize, Buffer);
+  }
+
+  return EFI_UNSUPPORTED;
 }