Re: [PATCH v2] hw/ide/core: Fix possible crash via NULL pointer in ide_cancel_dma_sync()

On 21/07/2026 08:02, Thomas Huth wrote:

> From: Thomas Huth <[email protected]>
> 
> ide_cancel_dma_sync() is called with a "IDEState *s" for one of the
> two IDE drives on a bus (primary or secondary drive) to cancel all
> pending DMA transfers on the drive. The code then checks
> s->bus->dma->aiocb to see whether there is any IO in flight on the
> *bus* and then calls blk_drain(s->blk) to wait for its completion.
> However, s->bus->dma->aiocb might belong to the other drive on the
> bus, and if there is no disk attached to the current drive, s->blk
> is NULL. Since blk_drain() does not check its parameter for a NULL
> pointer, QEMU can crash in such a case.
> 
> To fix the problem, we have to check that "blk" is not NULL before
> calling blk_drain(). And we have to call blk_drain() for both drives,
> otherwise the assert(s->bus->dma->aiocb == NULL) statement after
> the blk_drain() might trigger if the IO in flight belongs to the
> the other drive.
> 
> Resolves: https://urldefense.proofpoint.com/v2/url?u=https-3A__gitlab.com_qemu-2Dproject_qemu_-2D_work-5Fitems_905&d=DwIDAg&c=s883GpUCOChKOHiocYtGcg&r=c23RpsaH4D2MKyD3EPJTDa0BAxz6tV8aUJqVSoytEiY&m=BbZFP82dEZMyWzN5GnJ9XaxwmyrmYGbqWbEBNSUM_afB5JRRF3InIaZAr5UpUUh2&s=rCgSz13wVfk11Z-Uw5WTQViAQKkSvwpQqf_dJX1tiro&e=
> Reported-by: Alexander Bulekov <[email protected]>
> Resolves: https://urldefense.proofpoint.com/v2/url?u=https-3A__gitlab.com_qemu-2Dproject_qemu_-2D_work-5Fitems_4052&d=DwIDAg&c=s883GpUCOChKOHiocYtGcg&r=c23RpsaH4D2MKyD3EPJTDa0BAxz6tV8aUJqVSoytEiY&m=BbZFP82dEZMyWzN5GnJ9XaxwmyrmYGbqWbEBNSUM_afB5JRRF3InIaZAr5UpUUh2&s=B-AkqMAsQwA0LzU5ptwPJ3ZIBAA8ncf5ZbQg8GTwaME&e=
> Reported-by: dong ling
> Signed-off-by: Thomas Huth <[email protected]>
> ---
>   v2: Drain both drives
> 
>   hw/ide/core.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index f78b00220b8..f43ab95b07b 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -741,10 +741,17 @@ void ide_cancel_dma_sync(IDEState *s)
>        * In the future we'll be able to safely cancel the I/O if the
>        * whole DMA operation will be submitted to disk with a single
>        * aio operation with preadv/pwritev.
> +     *
> +     * Note: s->bus->dma->aiocb might belong to the adjacent IDEState,
> +     * so we have to drain both drives to get it cleared.
>        */
>       if (s->bus->dma->aiocb) {
>           trace_ide_cancel_dma_sync_remaining();
> -        blk_drain(s->blk);
> +        for (int i = 0; i < 2; i++) {
> +            if (s->bus->ifs[i].blk) {
> +                blk_drain(s->bus->ifs[i].blk);
> +            }
> +        }
>           assert(s->bus->dma->aiocb == NULL);
>       }
>   }

Doesn't ide_bus_active_if() do the right thing here for in-flight 
requests? I'd expect to be able to do something like:

   if (s->bus->dma->aiocb) {
       trace_ide_cancel_dma_sync_remaining();
       blk_drain(ide_bus_active_if(s->bus)->blk);
   }


ATB,

Mark.