Re: [RFC PATCH] netlink: Safer deletion of sk_bind_node

From: David Miller
Date: Tue Sep 02 2014 - 14:52:21 EST

From: Harish Jenny Kandiga Nagaraj <harish_kandiga@xxxxxxxxxx>
Date: Tue, 2 Sep 2014 14:14:38 +0530

> In one of our random test runs we observed the crash mentioned in the previous mail.
> After debugging we found out that the call flow of the inline and static functions were
> netlink_release
> -----netlink_remove
> ---------__sk_del_bind_node
> --------------__hlist_del
> *pprev was NULL in __hlist_del function while deleting &sk->sk_bind_node hlist_node. Hence the patch was given.
> In netlink_remove function , first the sk_del_node_init function will be called. This internally calls __sk_del_node_init function. While deleting &sk->sk_node hlist_node using __sk_del_node function there is a NULL check with sk_hashed function.
> Why there is no NULL check for *pprev while deleting &sk->sk_bind_node ?

Because if ->subscriptions is non-zero, it must be on a list, and therefore
pprev must be non-NULL.
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