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

[Like Xu <like.xu.linux@gmail.com>]

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(-)

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
-- 
2.41.0