Re: [PATCH] hw/scsi/megasas: Fix possible out-of-bounds array access in tracepoints

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 6/15/20 9:26 AM, Thomas Huth wrote:
> Some tracepoints in megasas.c use a guest-controlled value as an index
> into the mfi_frame_desc[] array. Thus a malicious guest could cause an
> out-of-bounds error here. Fortunately, the impact is very low since this
> can only happen when the corresponding tracepoints have been enabled
> before, but the problem should be fixed anyway with a proper check.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1882065
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  hw/scsi/megasas.c | 36 +++++++++++++++++++++++-------------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
> index af18c88b65..aa930226f8 100644
> --- a/hw/scsi/megasas.c
> +++ b/hw/scsi/megasas.c
> @@ -54,10 +54,6 @@
>  #define MEGASAS_FLAG_USE_QUEUE64   1
>  #define MEGASAS_MASK_USE_QUEUE64   (1 << MEGASAS_FLAG_USE_QUEUE64)
>  
> -static const char *mfi_frame_desc[] = {
> -    "MFI init", "LD Read", "LD Write", "LD SCSI", "PD SCSI",
> -    "MFI Doorbell", "MFI Abort", "MFI SMP", "MFI Stop"};
> -
>  typedef struct MegasasCmd {
>      uint32_t index;
>      uint16_t flags;
> @@ -183,6 +179,20 @@ static void megasas_frame_set_scsi_status(MegasasState *s,
>      stb_pci_dma(pci, frame + offsetof(struct mfi_frame_header, scsi_status), v);
>  }
>  
> +static inline const char *mfi_frame_desc(unsigned int cmd)
> +{
> +    static const char *mfi_frame_descs[] = {
> +        "MFI init", "LD Read", "LD Write", "LD SCSI", "PD SCSI",
> +        "MFI Doorbell", "MFI Abort", "MFI SMP", "MFI Stop"
> +    };
> +
> +    if (cmd < ARRAY_SIZE(mfi_frame_descs)) {
> +        return mfi_frame_descs[cmd];
> +    }
> +
> +    return "Unknown";
> +}
> +
>  /*
>   * Context is considered opaque, but the HBA firmware is running
>   * in little endian mode. So convert it to little endian, too.
> @@ -1670,25 +1680,25 @@ static int megasas_handle_scsi(MegasasState *s, MegasasCmd *cmd,
>      if (is_logical) {
>          if (target_id >= MFI_MAX_LD || lun_id != 0) {
>              trace_megasas_scsi_target_not_present(
> -                mfi_frame_desc[frame_cmd], is_logical, target_id, lun_id);
> +                mfi_frame_desc(frame_cmd), is_logical, target_id, lun_id);
>              return MFI_STAT_DEVICE_NOT_FOUND;
>          }
>      }
>      sdev = scsi_device_find(&s->bus, 0, target_id, lun_id);
>  
>      cmd->iov_size = le32_to_cpu(cmd->frame->header.data_len);
> -    trace_megasas_handle_scsi(mfi_frame_desc[frame_cmd], is_logical,
> +    trace_megasas_handle_scsi(mfi_frame_desc(frame_cmd), is_logical,
>                                target_id, lun_id, sdev, cmd->iov_size);
>  
>      if (!sdev || (megasas_is_jbod(s) && is_logical)) {
>          trace_megasas_scsi_target_not_present(
> -            mfi_frame_desc[frame_cmd], is_logical, target_id, lun_id);
> +            mfi_frame_desc(frame_cmd), is_logical, target_id, lun_id);
>          return MFI_STAT_DEVICE_NOT_FOUND;
>      }
>  
>      if (cdb_len > 16) {
>          trace_megasas_scsi_invalid_cdb_len(
> -                mfi_frame_desc[frame_cmd], is_logical,
> +                mfi_frame_desc(frame_cmd), is_logical,
>                  target_id, lun_id, cdb_len);
>          megasas_write_sense(cmd, SENSE_CODE(INVALID_OPCODE));
>          cmd->frame->header.scsi_status = CHECK_CONDITION;
> @@ -1706,7 +1716,7 @@ static int megasas_handle_scsi(MegasasState *s, MegasasCmd *cmd,
>      cmd->req = scsi_req_new(sdev, cmd->index, lun_id, cdb, cmd);
>      if (!cmd->req) {
>          trace_megasas_scsi_req_alloc_failed(
> -                mfi_frame_desc[frame_cmd], target_id, lun_id);
> +                mfi_frame_desc(frame_cmd), target_id, lun_id);
>          megasas_write_sense(cmd, SENSE_CODE(NO_SENSE));
>          cmd->frame->header.scsi_status = BUSY;
>          s->event_count++;
> @@ -1751,17 +1761,17 @@ static int megasas_handle_io(MegasasState *s, MegasasCmd *cmd, int frame_cmd)
>      }
>  
>      trace_megasas_handle_io(cmd->index,
> -                            mfi_frame_desc[frame_cmd], target_id, lun_id,
> +                            mfi_frame_desc(frame_cmd), target_id, lun_id,
>                              (unsigned long)lba_start, (unsigned long)lba_count);
>      if (!sdev) {
>          trace_megasas_io_target_not_present(cmd->index,
> -            mfi_frame_desc[frame_cmd], target_id, lun_id);
> +            mfi_frame_desc(frame_cmd), target_id, lun_id);
>          return MFI_STAT_DEVICE_NOT_FOUND;
>      }
>  
>      if (cdb_len > 16) {
>          trace_megasas_scsi_invalid_cdb_len(
> -            mfi_frame_desc[frame_cmd], 1, target_id, lun_id, cdb_len);
> +            mfi_frame_desc(frame_cmd), 1, target_id, lun_id, cdb_len);
>          megasas_write_sense(cmd, SENSE_CODE(INVALID_OPCODE));
>          cmd->frame->header.scsi_status = CHECK_CONDITION;
>          s->event_count++;
> @@ -1781,7 +1791,7 @@ static int megasas_handle_io(MegasasState *s, MegasasCmd *cmd, int frame_cmd)
>                              lun_id, cdb, cmd);
>      if (!cmd->req) {
>          trace_megasas_scsi_req_alloc_failed(
> -            mfi_frame_desc[frame_cmd], target_id, lun_id);
> +            mfi_frame_desc(frame_cmd), target_id, lun_id);
>          megasas_write_sense(cmd, SENSE_CODE(NO_SENSE));
>          cmd->frame->header.scsi_status = BUSY;
>          s->event_count++;
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>