Re: [PATCH] xen/sched: fix scheduler callback verification on init

[Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>]

On 4/10/26 19:40, Ruslan Ruslichenko wrote:
> From: Ruslan Ruslichenko <Ruslan_Ruslichenko@xxxxxxxx>
> 
> During core scheduler initialization, each registered scheduler
> is sanity tested in two steps:
> 
> - it must provide required callbacks (e.g. init, do_schedule).
> - if global_init callback is present, it must succeed.
> 
> If any of the steps fail, scheduler entry is cleared in global
> 'schedulers' array.
> 
> However, in the current implementation, if verification fails during
> the first step, the scheduler entry is cleared but verification
> sequence is not interrupted. This lead to NULL pointer dereference
> when subsequent required callbacks verified, and possible during
> the second step.
> 
> The patch fixes the crashes by adding check inside sched_test_func
> macro and skipping the call to a global_init if first step did not pass.
> 
> Signed-off-by: Ruslan Ruslichenko <Ruslan_Ruslichenko@xxxxxxxx>
> ---
>   xen/common/sched/core.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> index a57d5dd929..4270c89491 100644
> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -3017,7 +3017,7 @@ void __init scheduler_init(void)
>       for ( i = 0; i < NUM_SCHEDULERS; i++)
>       {
>   #define sched_test_func(f)                               \
> -        if ( !schedulers[i]->f )                         \
> +        if ( schedulers[i] && !schedulers[i]->f )        \
>           {                                                \
>               printk("scheduler %s misses .%s, dropped\n", \
>                      schedulers[i]->opt_name, #f);         \
 >               schedulers[i] = NULL;                        \

Maybe it would be cleaner to just add "continue" here?

> @@ -3034,6 +3034,9 @@ void __init scheduler_init(void)
>   
>   #undef sched_test_func
>   
> +        if ( !schedulers[i] )
> +            continue;
> +
>           if ( schedulers[i]->global_init && schedulers[i]->global_init() < 0 
> )
>           {
>               printk("scheduler %s failed initialization, dropped\n",

-- 
Mykyta