Re: [PATCH] KVM: eventfd: fix NULL deref irqbypass producer

[Alex Williamson]

On Tue,  1 Aug 2023 16:54:08 +0800
Like Xu <like.xu.linux@xxxxxxxxx> wrote:

> From: Like Xu <likexu@xxxxxxxxxxx>
> 
> Adding guard logic to make irq_bypass_register/unregister_producer()
> looks for the producer entry based on producer pointer itself instead
> of pure token matching.
> 
> As was attempted commit 4f3dbdf47e15 ("KVM: eventfd: fix NULL deref
> irqbypass consumer"), two different producers may occasionally have two
> identical eventfd's. In this case, the later producer may unregister
> the previous one after the registration fails (since they share the same
> token), then NULL deref incurres in the path of deleting producer from
> the producers list.
> 
> Registration should also fail if a registered producer changes its
> token and registers again via the same producer pointer.
> 
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> ---
>  virt/lib/irqbypass.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)


Reviewed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>


> 
> diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
> index 28fda42e471b..e0aabbbf27ec 100644
> --- a/virt/lib/irqbypass.c
> +++ b/virt/lib/irqbypass.c
> @@ -98,7 +98,7 @@ int irq_bypass_register_producer(struct irq_bypass_producer *producer)
>  	mutex_lock(&lock);
>  
>  	list_for_each_entry(tmp, &producers, node) {
> -		if (tmp->token == producer->token) {
> +		if (tmp->token == producer->token || tmp == producer) {
>  			ret = -EBUSY;
>  			goto out_err;
>  		}
> @@ -148,7 +148,7 @@ void irq_bypass_unregister_producer(struct irq_bypass_producer *producer)
>  	mutex_lock(&lock);
>  
>  	list_for_each_entry(tmp, &producers, node) {
> -		if (tmp->token != producer->token)
> +		if (tmp != producer)
>  			continue;
>  
>  		list_for_each_entry(consumer, &consumers, node) {
> 
> base-commit: 5a7591176c47cce363c1eed704241e5d1c42c5a6