Re: [Qemu-devel] [PATCH] ide: ahci: add check to avoid null dereference (CVE-2019-12067)

[Philippe Mathieu-Daudé]

Hi Prasad,

On 8/8/19 8:56 AM, P J P wrote:
> From: Prasad J Pandit <address@hidden>
> 
> AHCI emulator while committing DMA buffer in ahci_commit_buf()
> may do a NULL dereference if the command header 'ad->cur_cmd'
> is null. Add check to avoid it.
> 
> Reported-by: Bugs SysSec <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
>  hw/ide/ahci.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index 00ba422a48..9fff94075b 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -1458,8 +1458,10 @@ static void ahci_commit_buf(IDEDMA *dma, uint32_t 
> tx_bytes)
>  {
>      AHCIDevice *ad = DO_UPCAST(AHCIDevice, dma, dma);
>  
> -    tx_bytes += le32_to_cpu(ad->cur_cmd->status);
> -    ad->cur_cmd->status = cpu_to_le32(tx_bytes);
> +    if (ad->cur_cmd) {

My 2 cents, John will correct me:

This is not a valid condition, so an assert() might be more appropriate
here.

Why is dma_buf_commit() being called with a null command? This check
should go elsewhere to avoid the call.

> +        tx_bytes += le32_to_cpu(ad->cur_cmd->status);
> +        ad->cur_cmd->status = cpu_to_le32(tx_bytes);
> +    }
>  }
>  
>  static int ahci_dma_rw_buf(IDEDMA *dma, int is_write)
>