util/async.c: Forbid negative min/max in aio_context_set_thread_pool_params()

aio_context_set_thread_pool_params() takes two int64_t arguments to
set the minimum and maximum number of threads in the pool.  We do
some bounds checking on these, but we don't catch the case where the
inputs are negative.  This means that later in the function when we
assign these inputs to the AioContext::thread_pool_min and
::thread_pool_max fields, which are of type int, the values might
overflow the smaller type.

A negative number of threads is meaningless, so make
aio_context_set_thread_pool_params() return an error if either min or
max are negative.

Resolves: Coverity CID 1547605
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 util/async.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On 23/7/24 17:09, Peter Maydell wrote:
> aio_context_set_thread_pool_params() takes two int64_t arguments to
> set the minimum and maximum number of threads in the pool.  We do
> some bounds checking on these, but we don't catch the case where the
> inputs are negative.  This means that later in the function when we
> assign these inputs to the AioContext::thread_pool_min and
> ::thread_pool_max fields, which are of type int, the values might
> overflow the smaller type.
> 
> A negative number of threads is meaningless, so make
> aio_context_set_thread_pool_params() return an error if either min or
> max are negative.
> 
> Resolves: Coverity CID 1547605
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   util/async.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/util/async.c b/util/async.c
> index 0467890052a..3e3e4fc7126 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -746,7 +746,7 @@ void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
>                                           int64_t max, Error **errp)
>   {
>   
> -    if (min > max || !max || min > INT_MAX || max > INT_MAX) {
> +    if (min > max || max <= 0 || min < 0 || min > INT_MAX || max > INT_MAX) {
>           error_setg(errp, "bad thread-pool-min/thread-pool-max values");
>           return;
>       }

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

I don't get the point of using signed min/max here...

On Tue, 23 Jul 2024 at 16:44, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>
> On 23/7/24 17:09, Peter Maydell wrote:
> > aio_context_set_thread_pool_params() takes two int64_t arguments to
> > set the minimum and maximum number of threads in the pool.  We do
> > some bounds checking on these, but we don't catch the case where the
> > inputs are negative.  This means that later in the function when we
> > assign these inputs to the AioContext::thread_pool_min and
> > ::thread_pool_max fields, which are of type int, the values might
> > overflow the smaller type.
> >
> > A negative number of threads is meaningless, so make
> > aio_context_set_thread_pool_params() return an error if either min or
> > max are negative.
> >
> > Resolves: Coverity CID 1547605
> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> > ---
> >   util/async.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/util/async.c b/util/async.c
> > index 0467890052a..3e3e4fc7126 100644
> > --- a/util/async.c
> > +++ b/util/async.c
> > @@ -746,7 +746,7 @@ void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
> >                                           int64_t max, Error **errp)
> >   {
> >
> > -    if (min > max || !max || min > INT_MAX || max > INT_MAX) {
> > +    if (min > max || max <= 0 || min < 0 || min > INT_MAX || max > INT_MAX) {
> >           error_setg(errp, "bad thread-pool-min/thread-pool-max values");
> >           return;
> >       }
>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>
> I don't get the point of using signed min/max here...

I think this is because those values may originate in a
QAPI command structure (EventLoopBaseProperties), where
they are defined as "int" rather than a specifically
unsigned type. So we carry them around as int64_t until
they get to here, where we do the validation of whether
they're sensible or not.

thanks
-- PMM

On 23/7/24 17:51, Peter Maydell wrote:
> On Tue, 23 Jul 2024 at 16:44, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>>
>> On 23/7/24 17:09, Peter Maydell wrote:
>>> aio_context_set_thread_pool_params() takes two int64_t arguments to
>>> set the minimum and maximum number of threads in the pool.  We do
>>> some bounds checking on these, but we don't catch the case where the
>>> inputs are negative.  This means that later in the function when we
>>> assign these inputs to the AioContext::thread_pool_min and
>>> ::thread_pool_max fields, which are of type int, the values might
>>> overflow the smaller type.
>>>
>>> A negative number of threads is meaningless, so make
>>> aio_context_set_thread_pool_params() return an error if either min or
>>> max are negative.
>>>
>>> Resolves: Coverity CID 1547605
>>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>>> ---
>>>    util/async.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/util/async.c b/util/async.c
>>> index 0467890052a..3e3e4fc7126 100644
>>> --- a/util/async.c
>>> +++ b/util/async.c
>>> @@ -746,7 +746,7 @@ void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
>>>                                            int64_t max, Error **errp)
>>>    {
>>>
>>> -    if (min > max || !max || min > INT_MAX || max > INT_MAX) {
>>> +    if (min > max || max <= 0 || min < 0 || min > INT_MAX || max > INT_MAX) {
>>>            error_setg(errp, "bad thread-pool-min/thread-pool-max values");
>>>            return;
>>>        }
>>
>> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>>
>> I don't get the point of using signed min/max here...
> 
> I think this is because those values may originate in a
> QAPI command structure (EventLoopBaseProperties), where
> they are defined as "int" rather than a specifically
> unsigned type. So we carry them around as int64_t until
> they get to here, where we do the validation of whether
> they're sensible or not.

Ah indeed. Probably very old code hard to change now
(QAPI does support unsigned types).

On Tue, Jul 23, 2024 at 04:09:27PM +0100, Peter Maydell wrote:
> aio_context_set_thread_pool_params() takes two int64_t arguments to
> set the minimum and maximum number of threads in the pool.  We do
> some bounds checking on these, but we don't catch the case where the
> inputs are negative.  This means that later in the function when we
> assign these inputs to the AioContext::thread_pool_min and
> ::thread_pool_max fields, which are of type int, the values might
> overflow the smaller type.
> 
> A negative number of threads is meaningless, so make
> aio_context_set_thread_pool_params() return an error if either min or
> max are negative.
> 
> Resolves: Coverity CID 1547605
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  util/async.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, applied to my block tree:
https://gitlab.com/stefanha/qemu/commits/block

Stefan