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

On 20/7/26 21:42, 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.
> 
> Fix the problem by checking s->blk to be a valid pointer before
> calling blk_drain() in this function.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/905
> Reported-by: Alexander Bulekov <[email protected]>
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4052
> Reported-by: dong ling
> Signed-off-by: Thomas Huth <[email protected]>
> ---
>   hw/ide/core.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index f78b00220b8..49848c8e6bd 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -741,8 +741,11 @@ 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 check s->blk for not being NULL, too.
>        */
> -    if (s->bus->dma->aiocb) {
> +    if (s->bus->dma->aiocb && s->blk) {

Reviewed-by: Philippe Mathieu-Daudé <[email protected]>

If you don't object, I'll change to:

        if (s->blk && s->bus->dma->aiocb) {

when queueing.

>           trace_ide_cancel_dma_sync_remaining();
>           blk_drain(s->blk);
>           assert(s->bus->dma->aiocb == NULL);