On Fri, Oct 4, 2024 at 9:55 AM Eric Dumazet edumazet@google.com wrote:
On Thu, Oct 3, 2024 at 11:50 PM Kuniyuki Iwashima kuniyu@amazon.com wrote:
From: Ignat Korchagin ignat@cloudflare.com Date: Thu, 3 Oct 2024 18:01:51 +0100
We have recently noticed the exact same KASAN splat as in commit 6cd4a78d962b ("net: do not leave a dangling sk pointer, when socket creation fails"). The problem is that commit did not fully address the problem, as some pf->create implementations do not use sk_common_release in their error paths.
For example, we can use the same reproducer as in the above commit, but changing ping to arping. arping uses AF_PACKET socket and if packet_create fails, it will just sk_free the allocated sk object.
While we could chase all the pf->create implementations and make sure they NULL the freed sk object on error from the socket, we can't guarantee future protocols will not make the same mistake.
So it is easier to just explicitly NULL the sk pointer upon return from pf->create in __sock_create. We do know that pf->create always releases the allocated sk object on error, so if the pointer is not NULL, it is definitely dangling.
Sounds good to me.
Let's remove the change by 6cd4a78d962b that should be unnecessary with this patch.
Reviewed-by: Eric Dumazet edumazet@google.com
Even if not strictly needed we also could fix af_packet to avoid a dangling pointer.
af_packet was just one example - I reviewed every pf->create function and there are others. It would not be fair to fix this, but not the others, right?
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index a705ec21425409dc708cf61d619545ed342b1f01..db7d3482e732f236ec461b1ff52a264d1b93bf90 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3421,16 +3421,18 @@ static int packet_create(struct net *net, struct socket *sock, int protocol, if (sock->type == SOCK_PACKET) sock->ops = &packet_ops_spkt;
po = pkt_sk(sk);err = packet_alloc_pending(po);if (err)goto out2;/* No more error after this point. */ sock_init_data(sock, sk);
po = pkt_sk(sk); init_completion(&po->skb_completion); sk->sk_family = PF_PACKET; po->num = proto;err = packet_alloc_pending(po);if (err)goto out2; packet_cached_dev_reset(po);