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

On 20/07/2026 22.36, Philippe Mathieu-Daudé wrote:
> 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.
Please unqueue it again - I just noticed that it is now possible to trigger 
the assert(s->bus->dma->aiocb == NULL) after the blk_drain() instead...
I think we simply have to drain both drives, primary and secondary, if their 
"blk" is not NULL... I'll send a v2.

  Thomas