Re: [PATCH v2 1/8] net: explicitly clear the sk pointer, when pf->create fails

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Ignat Korchagin <ignat@cloudflare.com>
Date: Mon,  7 Oct 2024 22:34:55 +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.
> 
> Fixes: 6cd4a78d962b ("net: do not leave a dangling sk pointer, when socket creation fails")
> Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>