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
