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    SubjectRe: [PATCH] KVM: eventfd: fix NULL deref irqbypass producer
    On Tue,  1 Aug 2023 16:54:08 +0800
    Like Xu <like.xu.linux@gmail.com> wrote:

    > From: Like Xu <likexu@tencent.com>
    >
    > 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@redhat.com>
    > Signed-off-by: Like Xu <likexu@tencent.com>
    > ---
    > virt/lib/irqbypass.c | 4 ++--
    > 1 file changed, 2 insertions(+), 2 deletions(-)


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


    >
    > 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

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