Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/05/20 21:25, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While in megasas_handle_frame(), megasas_enqueue_frame() may
> set a NULL frame into MegasasCmd object for a given 'frame_addr'
> address. Add check to avoid a NULL pointer dereference issue.
> 
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/scsi/megasas.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
> index 6ce598cd69..b531d88a9b 100644
> --- a/hw/scsi/megasas.c
> +++ b/hw/scsi/megasas.c
> @@ -504,7 +504,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
>      cmd->pa = frame;
>      /* Map all possible frames */
>      cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
> -    if (frame_size_p != frame_size) {
> +    if (!cmd->frame || frame_size_p != frame_size) {
>          trace_megasas_qf_map_failed(cmd->index, (unsigned long)frame);
>          if (cmd->frame) {
>              megasas_unmap_frame(s, cmd);
> -- 2.25.4
> 

I think the code here was expecting frame_size_p to be 0 if cmd->frame
is NULL.  Can you check why this is not the case, or whether it ever was
the case?

Thanks,

Paolo