Re: [PATCH] OvmfPkg/VirtioFsDxe: call IsTimeValid() before EfiTimeToEpoch()

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 1/7/21 10:50 AM, Laszlo Ersek wrote:
> EmbeddedPkg/TimeBaseLib provides a verification function called
> IsTimeValid(), for enforcing the UEFI spec requirements on an EFI_TIME
> object.
> 
> When EFI_FILE_PROTOCOL.SetInfo() is called in order to update the
> timestamps on the file, let's invoke IsTimeValid() first, before passing
> the new EFI_FILE_INFO.{CreateTime,LastAccessTime,ModificationTime} values
> to EfiTimeToEpoch().
> 
> This patch is not expected to make a practical difference, but it's better
> to ascertain the preconditions of EfiTimeToEpoch() on the
> EFI_FILE_PROTOCOL.SetInfo() caller. The FAT driver (EnhancedFatDxe) has a
> similar check, namely in FatSetFileInfo() -> FatIsValidTime().
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>


> ---
>  OvmfPkg/VirtioFsDxe/Helpers.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/OvmfPkg/VirtioFsDxe/Helpers.c b/OvmfPkg/VirtioFsDxe/Helpers.c
> index 443bbdc616ac..b81c04e0a4e8 100644
> --- a/OvmfPkg/VirtioFsDxe/Helpers.c
> +++ b/OvmfPkg/VirtioFsDxe/Helpers.c
> @@ -2237,26 +2237,33 @@ VirtioFsGetFuseSizeUpdate (
>  
>    @param[out] Atime        If UpdateAtime is set to TRUE, then Atime provides
>                             the last access timestamp to set (as seconds since
>                             the Epoch). Otherwise, Atime is not written to.
>  
>    @param[out] Mtime        If UpdateMtime is set to TRUE, then Mtime provides
>                             the last modification timestamp to set (as seconds
>                             since the Epoch). Otherwise, Mtime is not written
>                             to.
>  
> -  @retval EFI_SUCCESS        Output parameters have been set successfully.
> +  @retval EFI_SUCCESS            Output parameters have been set successfully.
>  
> -  @retval EFI_ACCESS_DENIED  NewInfo requests changing both CreateTime and
> -                             ModificationTime, but to values that differ from
> -                             each other. The Virtio Filesystem device does not
> -                             support this.
> +  @retval EFI_INVALID_PARAMETER  At least one of the CreateTime, LastAccessTime
> +                                 and ModificationTime fields in NewInfo
> +                                 represents an actual update relative to the
> +                                 current state of the file (expressed in Info),
> +                                 but does not satisfy the UEFI spec
> +                                 requirements on EFI_TIME.
> +
> +  @retval EFI_ACCESS_DENIED      NewInfo requests changing both CreateTime and
> +                                 ModificationTime, but to values that differ
> +                                 from each other. The Virtio Filesystem device
> +                                 does not support this.
>  **/
>  EFI_STATUS
>  VirtioFsGetFuseTimeUpdates (
>    IN     EFI_FILE_INFO *Info,
>    IN     EFI_FILE_INFO *NewInfo,
>       OUT BOOLEAN       *UpdateAtime,
>       OUT BOOLEAN       *UpdateMtime,
>       OUT UINT64        *Atime,
>       OUT UINT64        *Mtime
>    )
> @@ -2278,20 +2285,23 @@ VirtioFsGetFuseTimeUpdates (
>    //
>    // Determine which timestamps differ from the current state. (A zero time
>    // means "don't update", per UEFI spec.) For each timestamp that's being
>    // changed, calculate the seconds since the Epoch.
>    //
>    for (Idx = 0; Idx < ARRAY_SIZE (Time); Idx++) {
>      if (CompareMem (NewTime[Idx], &ZeroTime, sizeof (EFI_TIME)) == 0 ||
>          CompareMem (NewTime[Idx], Time[Idx], sizeof (EFI_TIME)) == 0) {
>        Change[Idx] = FALSE;
>      } else {
> +      if (!IsTimeValid (NewTime[Idx])) {
> +        return EFI_INVALID_PARAMETER;
> +      }
>        Change[Idx] = TRUE;
>        Seconds[Idx] = EfiTimeToEpoch (NewTime[Idx]);
>      }
>    }
>  
>    //
>    // If a change is requested for exactly one of CreateTime and
>    // ModificationTime, we'll change the last modification time. If changes are
>    // requested for both, and to the same timestamp, we'll similarly update the
>    // last modification time. If changes are requested for both, but to
>